TY - JOUR
AU1 - Zhdanov, Oleksandr
AU2 - Blatt, Michael R
AU3 - Zare-Behtash, Hossein
AU4 - Busse, Angela
AB - Abstract Plants are known to exhibit a thigmomorphogenetic response to mechanical stimuli by altering their morphology and mechanical properties. Wind is widely perceived as mechanical stress and in many experiments its influence is simulated by applying mechanical perturbations. However, it is known that wind-induced effects on plants can differ and at times occur even in the opposite direction compared with those induced by mechanical perturbations. In the present study, the long-term response of Arabidopsis thaliana to a constant unidirectional wind was investigated. We found that exposure to wind resulted in a positive anemotropic response and in significant alterations to Arabidopsis morphology, mechanical properties, and anatomical tissue organization that were associated with the plant’s strategy of acclimation to a windy environment. Overall, the observed response of Arabidopsis to wind differs significantly from previously reported responses of Arabidopsis to mechanical perturbations. The presented results suggest that the response of Arabidopsis is sensitive to the type of mechanical stimulus applied, and that it is not always straightforward to simulate one type of perturbation by another. Anemotropic response, Arabidopsis thaliana, biomechanics, mechanical properties, morphology, stem anatomy, thigmomorphogenesis, wind Introduction Current predictions on global warming show that the global average temperature will increase by 1.5 °C compared with pre-industrial levels by 2030–2050 (Allen et al., 2018). Among other climatic changes, this will lead to alterations in wind speeds and patterns. Global climate simulation models show that the predicted increase in the global temperature will lead to a significant increase in surface wind speeds over the UK and Northern Europe (Hosking et al., 2018). Similar trends have been found for other parts of the world; for example, analysis of the wind speed data for China demonstrated an increase in the wind speeds measured during spring and summer months over the last 40 years (Zhang et al., 2020). Strong winds and storms have a negative impact on food security, since for crop plants (e.g. wheat, rice, and maize) wind-induced stem and root lodging significantly affects yields (Berry et al., 2004). An overview of the reported yield reductions in major crop plants due to lodging shows that it can reach up to 80% in wheat, 83.9% in rice, 65% in barley, 40% in oats, and 20% in maize (Shah et al., 2017). Wind also has an economic impact on wood production, since windthrow due to strong winds poses a serious threat to forests (Mitchell, 2013). The review by Schelhaas et al. (2003) showed that damage from windstorms to forests in Europe contributes >50% to the total damage from all natural causes. In their natural environment, plants are typically subjected to low and moderate wind conditions on a regular basis, since they cannot shelter themselves from wind. This interaction can have either beneficial or detrimental effects, and plants have developed a number of strategies to adapt and survive. Detailed reviews of these effects and strategies are given in De Langre (2008) and Gardiner et al. (2016). Wind is a complex environmental factor (Ennos, 1997; Jones, 2013) that among other effects regulates the microclimate of plants, can alter photosynthesis (Smith and Ennos, 2003; Burgess et al., 2016), and can change heat and mass transfer in plants (Jones, 2013). One of the most direct effects of wind on plants is the mechanical stress exerted on plants through the drag force. This, as in the case of mechanical stress induced by mechanical perturbations (e.g. brushing or touching), evokes physiological and morphological responses in plants known under the term thigmomorphogenesis first introduced by Jaffe (1973). Typically, thigmomorphogenesis leads to the inhibition of the stem length and an increase of its diameter, thus plants develop shorter but thicker stems (see, for example, Biddington, 1986; Jaffe and Forbes, 1993). In addition, mechanical perturbations reduce a plant’s aboveground biomass (Niklas, 1998; Kern et al., 2005). Similar effects were noticed in plants, especially trees, that are exposed to wind and experience mechanical stress, mainly in the form of bending (Lawton, 1982; Biddington, 1986). These observations inspired numerous studies where mechanical perturbations, such as bending or touching, were utilized to mimic the influence of wind on various plants (e.g. Gartner, 1994; Niklas, 1998). However, the wind–plant interaction involves fluid (air) to solid (plant) contact and can be considered a fluid dynamic perturbation as opposed to a mechanical perturbation in the form of brushing or touching where direct solid to solid contact is present. Different types of perturbations may induce different effects on plants. Indeed, factorial experiments where the response to wind and mechanical perturbations was studied separately on the same plant species have shown that wind can have different and even opposite effects to mechanical perturbations (Smith and Ennos, 2003; Anten et al., 2010). The different response of the same plant to wind compared with mechanical perturbations suggests that implicit extrapolation of results obtained from tests with mechanical perturbations (e.g. brushing or flexing) to the effects of wind is not always correct (Anten et al., 2010). Arabidopsis thaliana, a small annual herbaceous plant, is widely used in plant science as a model organism to study different processes and mechanisms especially in the field of plant genetics and molecular biology (Koornneef and Meinke, 2010). Arabidopsis Columbia (Col-0) is commonly utilized as the reference genotype in plant science, but many other natural accessions as well as mutants of this plant exist and have been subjected to a wide range of investigations (Lamesch et al., 2012). Brulé et al. (2016) suggested that Arabidopsis can be used, with certain limitations, as a model plant to investigate the influence of different parameters on plant stiffness. The response of Arabidopsis to various mechanical perturbations was explored in a number of studies and is well documented (Braam, 2005; Chehab et al., 2009; Paul-Victor and Rowe, 2011). In addition, investigation of thigmomorphogenesis in Arabidopsis at the molecular level identified a set of touch-induced genes whose expression is enhanced in response to various stimuli (Braam and Davis, 1990). In general, mechanical perturbations of Arabidopsis result in a response that is common to many other plants, namely reduction of the stem length. Mechanical characterization of the primary inflorescence stems showed that perturbed plants were less rigid and had a decreased elastic modulus compared with the control group, thus suggesting that Arabidopsis follows the ‘short and flexible strategy’ for stem development in order to cope with mechanical stress (Paul-Victor and Rowe, 2011). From these experiments, it was conjectured that exposure to wind will have the same effects on Arabidopsis Col-0. However, as mentioned previously, wind can have different and even opposite effects on plants compared with those from mechanical stimuli. Indeed, a limited number of studies where periodic wind treatment was applied to Arabidopsis show that even where the response was in the same direction, the magnitude of changes was not the same (e.g. Bossdorf and Pigliucci, 2009). However, in these experiments, the response to wind was analysed as an average across a number of Arabidopsis ecotypes and the response specific to Col-0 cannot be inferred. In addition, the mechanical characterization of inflorescence stems did not form part of this study. Consequently, the question remains open as to whether the response of Arabidopsis Col-0 to mechanical stress induced by fluid dynamic perturbations, namely wind, is the same as has been previously documented for mechanical stress induced by mechanical perturbations, such as brushing or touching. In addition, the effect of wind on mechanical properties of Arabidopsis, such as stem bending rigidity and Young’s modulus of elasticity, remains untested. In the present study, the influence of a constant unidirectional wind on Arabidopsis ecotype Col-0 is investigated. The results show that wind-treated plants exhibit a positive anemotropic response and their morphology is significantly altered. In addition, exposure to wind modified mechanical properties, anatomical tissue organization, and ion content of the primary inflorescence stems. The observed changes were related to the acclimation strategy of Arabidopsis to survive and develop under constant unidirectional wind. Overall, it was found that wind-induced changes to Arabidopsis differ from those reported previously as a result of mechanical perturbations in the form of brushing. These observations suggest that Arabidopsis is sensitive to the type of stimulus applied and that the substitution of one type of perturbation by another is not straightforward. This study contributes to the systematic understanding of the thigmomorphogenetic response of Arabidopsis and provides new insights into the response of plants to wind. Materials and methods Plants In this study, the response of Arabidopsis to wind was characterized using a range of techniques. Two experiments were carried out in order to obtain all measurements since the number of plants that could be subjected to the wind treatment simultaneously was limited to 21 in each experiment. Because of the different preparations, the quantitative results differ between the two data sets although the qualitative results are the same. For this reason, we report the results from the two data sets separately. In the first experiment, seeds of Arabidopsis ecotype Col-0 were sown in a single pot and kept at 4 °C for 48 h. The pot was then placed in the growth chamber with a long-day cycle (16 h of light and 8 h of darkness), temperature at 22 °C, light intensity at 150 μmol m−2 s−1, and humidity at 60%. After ~2 weeks, the seedlings were transplanted into individual pots and were kept in the same growth chamber. After 15 d, when the flower-bearing stem was about to start its development, plants were randomly separated into two groups and moved to the glasshouse. In the second experiment, the procedure was the same except that the plants were grown inside the glasshouse from its start. The first group (21 plants in both experiments) was subjected to a constant unidirectional flow in a purpose-built wind tunnel (experimental group), while the second group (19 plants in the first and 21 plants in the second experiment) was cultivated in the same glasshouse but without wind influence (control group). The conditions in the glasshouse for both groups were as follows, long-day cycle and minimum light intensity at 150 μmol m−2 s−1. The temperature and humidity inside the glasshouse exhibit diurnal variation and only minimum and maximum temperatures are controlled. However, when the wind tunnel was on, loggers placed inside the wind tunnel test section (Lascar EL-GFX-2) and outside of the test section (Elitech RC-61) showed that the conditions in terms of temperature and humidity experienced by the plants are the same in both groups. Wind treatment To study the influence of wind on Arabidopsis, a specialized wind tunnel was designed and built. The description of the wind tunnel together with the characterization of its test section using hot-wire anemometry is presented in the following section. The wind tunnel provides a well-controlled and characterized constant wind environment. In both experiments, plants were subjected to a unidirectional flow of a constant speed of 5 m s–1 with turbulence intensity of 2%. According to Bossdorf and Pigliucci (2009), who applied wind treatment of the same speed to Arabidopsis, this value is higher than the typical wind speed at a few decimetres above the surface, based on the mean wind speed data over Central Europe. In the UK, the mean wind speed at 10 m height above the surface level can reach up to 7.5 m s–1 (MetOffice, 2020). Assuming a logarithmic wind profile (Manwell et al., 2010), this value extrapolates to a maximum average speed of 2.4–3 m s–1 at the height of 20–30 cm above ground in open agricultural areas. Consequently, the wind speed of 5 m s–1 utilized in this study can be considered as a high wind for small plants such as Arabidopsis. The wind was applied for 24 h a day, and the total duration of the treatment was up to 17 d. Inside the test section, 21 pots with a single Arabidopsis plant were arranged in six staggered rows (four pots in the odd rows and three pots in the even). In order to minimize the influence of the pot position and ensure even exposure to the wind, the pots were swapped between rows and within each row every 4–5 d. The orientation of the plants with respect to the flow direction was preserved. The top edges of the pots were in line with the test section floor and the plants were regularly watered from the bottom. Wind tunnel The wind tunnel (Supplementary Fig. S1) is an open-circuit type with a closed test section and can be run continuously at a constant flow speed for the required duration of the experiment. The test section is 1 m long and has a rectangular cross-section of 0.45 m×0.4 m. The side walls and the ceiling of the test section are made of acrylic glass to provide optical access for monitoring the plants’ development and conditions. To straighten the flow and increase its uniformity, an aluminium honeycomb (cell size=6 mm) is installed at the test section inlet. The flow is created by an axial fan connected to the outlet of the test section through a diffusor and flexible connector. The flow speed is controlled by a variable transformer and can be set to any value in the range from 0.8 m s–1 to 10.5 m s–1. LED grow lights with a programmable timer are installed over the test section to control light intensity and the growth cycle. Characterization of the flow within the wind tunnel test section was performed using a Dantec Dynamics StreamLine Pro System. Measurements were conducted with a straight, single sensor probe (55P11). During the characterization procedure, the wind tunnel was equipped with a bespoke three-axis traverse system enabling a precise positioning of the hot-wire probe, and the standard acrylic glass panels in its doors were replaced with slotted panels to provide access for the probe to the interior. In situ calibration of the probe was performed before and after each measurement against pitot tube data. The pitot tube was connected to a dry cell standard micromanometer (DP Measurements TT570SV) and was inserted through a port in the top wall for the calibration procedure. The relationship between the squared sensor voltage (E) and effective cooling velocity (U) was established using King’s law (King, 1914): E2=E02+BUn(1) where E0 is the sensor voltage measured at zero velocity, B and n are King’s law coefficients. B and n were determined using simple linear regression after measuring the voltage across the sensor over a range of known flow velocities. The flow inside the test section was characterized in terms of the flow speed and turbulence intensity at several locations along its length. Measurements were taken in 2D planes normal to the flow direction. Each plane consisted of 80 points (10 in the horizontal and 8 in the vertical direction) with 40 mm spacing in each direction. Due to construction features of the wind tunnel test section frame, the offsets from the wind tunnel walls were 45 mm from the side walls and 60 mm from top and bottom walls. Data were sampled at 100 kHz for 10 s at each measuring point. The hot-wire measurements showed that the flow velocity inside the wind tunnel is stable over time and that the velocity distribution is uniform along the wind tunnel test section (see Supplementary Fig. S2). The average turbulence intensity inside the test section is ~2% for all tested flow speeds. Overall, the quality of the flow inside the wind tunnel is quite uniform and the plants experience similar conditions regardless of their location. Phenotyping To investigate the morphological response of Arabidopsis to the wind treatment, phenotyping of plants in both experimental and control groups was conducted at two time points during each experiment. The recorded parameters were the length of the primary inflorescence stem, the number of stems (basal branches), and the number of branches. The first phenotyping was conducted 34–38 days after sowing (DAS) when the average length of the primary inflorescence stem in the control group plants was >170 mm. All the parameters were measured again at 40–48 DAS in both experiments (6–10 d after the first phenotyping). The second reported experiment was shorter in time compared with the first one (12 d and 17 d of the wind treatment, respectively); however, the duration of the experiment does not affect the trends in the wind-induced changes to the Arabidopsis phenotype. In addition, the average diameters of the top and bottom parts of the primary inflorescence stems were measured from the photographs taken during the mechanical tests in the first experiment. In the second experiment, after the end of the wind treatment, the aboveground fresh biomass of 10 plants from both groups was assessed. After oven drying at 70 °C, the dry biomass was also determined. Mechanical characterization In the first experiment, the changes in mechanical properties of Arabidopsis primary inflorescence stems as a result of wind treatment were characterized by assessing their bending rigidity and Young’s modulus of elasticity. The former characterizes the ability of the material to resist bending, while the latter characterizes its resistance to elastic deformations. Mechanical characterization was conducted for all plants from the experimental (n=21) and control (n=19) groups on two segments taken from the same stem. The first segment was taken from the basal part of the stem, where the cells and tissues are the oldest and were subjected to the wind for the longest time. This part of the stem is referred to as the ‘bottom part of the stem’. The second segment was taken from the apex part of the stem, that was subjected to wind for a shorter period of time compared with the bottom part and is comprised of younger cells and tissues. This part of the stem is referred to as the ‘top part of the stem’. By investigating two different segments of the same stem, it is possible to check the distribution of the mechanical properties along its length and to study whether the changes resulting from the wind treatment are consistent. Both segments were cut using a razor blade and, if necessary, cleared of branches, fruits, flowers, and young floral buds. The tip part of the stem, containing the growth zone, was removed from the top part of the stem prior to testing. Mechanical characterization of Arabidopsis primary inflorescence stems was conducted using the dynamic forced vibration method (Zhdanov et al., 2020). In this method, the mechanical properties of the tested stem segments are estimated through their multiple resonant frequencies (fi) using Euler–Bernoulli beam theory (Blevins, 1979): fi=λi22πL2EIm, i=1,2,3,…, n(2) where L is the length of the stem, I is the second moment of area, m is the mass per unit length, and λ i is a dimensionless parameter that is obtained from the characteristic equation corresponding to the applied boundary conditions and vibration mode. In the present study, stem segments were tested with clamped-clamped boundary conditions. In all tests, the length of the tested stem segment was equal to 50 mm, corresponding to the distance between the clamping points. To evaluate I, a widely used approximation that a segment of Arabidopsis stem has a circular cross-section of constant diameter along its length was utilized (see, for example, Turner and Somerville, 1997; Bichet et al., 2001). The diameter was determined from the photographs of the tested stem segment taken after each test using ImageJ software (Schneider et al., 2012) as the averaged diameter over several locations. The mass of the segment was determined directly after each test using a precision balance; m was then evaluated as the ratio between the mass and the length of the segment. For the bottom part of the stem, the determined mechanical proprieties were averaged over the first three natural frequencies while for the top part the first four natural frequencies were used. The multiple resonant frequency method was previously validated against a standard three-point bending test (Zhdanov et al., 2020). The tests were performed immediately after the cutting of each segment to avoid changes in the mechanical properties of the stem segments due to dehydration and decrease in turgor pressure. Anatomical measurements In the second experiment, the anatomical tissue composition of the primary inflorescence stem was investigated for 10 plants from each group. Segments were taken from the basal and apex ends; that is, the same two parts of the stem were considered as for the mechanical characterization. The transverse segments were sectioned manually from the centre of these stem parts using a razor blade and stained with 0.02% toluidine blue. As a result of histochemical staining it was possible to differentiate three representative tissues, namely the outer part that consists of epidermis and cortex, the middle part that mostly accommodates lignified tissues (coloured in blue), and the innermost part—pith (coloured in purple). The samples were observed on a Zeiss Stemi SV11 microscope and photos were captured. The relative areas of the three aforementioned representative tissues were measured from the images using ImageJ software. Ca2+ measurements In the second experiment, bottom stem segments from eight plants in each group were collected and their fresh weight was determined. After drying for 48 h and recording the dry weight, the stems were homogenized, and dry material was extracted in 1 M HCl. The insoluble material was removed through centrifugation, retaining the supernatant. Aliquots of the supernatant were used to determine the Ca2+ content utilizing flame photometry (Model 410 flame photometer, Sherwood). All measurements were quantified against calibration standards. Statistical analysis All statistics of measured quantities are reported as the mean ±SD of n observations. The post-hoc statistical analysis was carried out with a non-parametric Wilcoxon rank-sum test. This test was chosen due to the small sample sizes of different lengths and because some of the data did not follow the normal distribution. The tests were performed in Matlab (R2015b, MathWorks, USA) using the in-built ranksum function. A statistically significant difference was established at P≤0.05. Results Due to the destructive nature of most of the conducted tests and limited room inside the wind tunnel test section, two sets of experiments were conducted in this study. The experiments were carried out at two different times of the year, hence the conditions inside the glasshouse were slightly different in terms of temperature and maximum light intensity. In addition, performing two sets of experiments provided the possibility to increase the sample size for statistics of the reported parameters. Where possible, the same tests were conducted in both sets of experiments (phenotyping). Despite the quantitative differences between the results obtained in the reported experiments, qualitatively they led to the same conclusions. Wind treatment induces changes in Arabidopsis phenotype The effect of wind treatment on the recorded morphological parameters was low compared with the control group during the first phenotyping in both experiments (see Fig. 1). The primary inflorescence stem of plants in the experimental group was on average shorter by 8.81% and 10.52% in the first and second experiments, respectively (Fig. 1A). However, the observed decrease is statistically significant (P<0.05) only in the second experiment. The average number of stems in the wind-treated plants at this stage was 2.33±0.73 and 2.24±0.78 in the first and second experiments, respectively (Fig. 1B). These values were lower compared with the control group where the number of stems was 2.79±1.13 and 3.95±0.86, respectively. The difference in average number of stems between the wind-treated plants and the control group was statistically significant only in the second experiment. The same effect was observed for the number of branches (Fig. 1C), namely plants from the experimental group had fewer branches in both experiments, 2.81±0.6 and 4.95±1.47, respectively, compared with 3.26±0.81 and 9.14±2.43 in the control groups. As in the case of the number of stems, this difference was statistically significant in the second experiment only. Fig. 1. Open in new tabDownload slide Changes to the morphological parameters as a result of unidirectional wind treatment with a constant flow speed of 5 m s–1 in both conducted experiments. (A) Length of the primary inflorescence stem. (B) Number of stems. (C) Number of branches. Error bars represent the SD. Statistically significant differences (P≤0.05) from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=19 and n=21 for the first and second experiments, respectively) and experimental (n=21 for both experiments) groups are marked with (*). Fig. 1. Open in new tabDownload slide Changes to the morphological parameters as a result of unidirectional wind treatment with a constant flow speed of 5 m s–1 in both conducted experiments. (A) Length of the primary inflorescence stem. (B) Number of stems. (C) Number of branches. Error bars represent the SD. Statistically significant differences (P≤0.05) from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=19 and n=21 for the first and second experiments, respectively) and experimental (n=21 for both experiments) groups are marked with (*). During the second phenotyping, which was conducted 10 d and 6 d after the first one in the first and second experiments, respectively, the wind effects became more substantial and statistically significant (see Fig. 1). The length of the primary inflorescence stem in both experiments was reduced only slightly compared with the control group plants (4.71% and 13.98%), but, in contrast to the first phenotyping, this difference became statistically significant (P<0.05) in all cases (Fig. 1A). In addition, both experiments showed that plants subjected to the unidirectional constant wind have fewer stems and branches compared with the untreated plants (Fig. 1B, C). The number of stems in the wind-treated plants recorded in both experiments was 5.1±0.7 and 3.24±0.62, respectively. These values are significantly lower (P<0.05) compared with 5.68±0.75 and 4.81±0.75 observed in the plants from the corresponding control groups. The highest effect of the wind treatment was measured for the number of branches. Plants from the experimental group had on average 24.05±4.96 and 9.38±2.44 branches (in experiments 1 and 2, respectively); this is lower by approximately one-third compared with the average number of branches in the plants from the control group (34.47±8.0 and 20.48±4.91), and this difference is statistically significant (P<0.0001). Wind treatment also resulted in a decrease in the diameter of the primary inflorescence stem segments that was measured after the first experiment (see Fig. 2). The bottom parts of the stem had significantly (P<0.05) lower diameter compared with those of the control group plants. The diameter of the top parts of the stem was also reduced, but the difference was statistically insignificant (P>0.05). The plants grown under a constant unidirectional wind had a significantly (P<0.05) lower aboveground fresh biomass (see Table 1). Fresh weight of the Arabidopsis Col-0 exposed to wind was less than half of the weight of the control plants. In addition, a significant (P<0.01) reduction by almost 48% in the dry aboveground biomass of the plants from the experimental group was also observed. On the other hand, the biomass ratio that was calculated as the percentage of moisture evaporated during oven drying was almost the same in both groups. Table 1. Overview of the changes to the Arabidopsis biomass (mean ±SD) that were assessed after the end of the unidirectional wind treatment with a constant flow speed of 5 m s–1 in the second experiment . Experiment 2 . . Control plants . Wind-treated plants . P-value . Fresh biomass, g 1.78±0.55 0.87±0.33 0.001 Dry biomass, g 0.23±0.06 0.12±0.04 0.001 Biomass ratio, % 86.7±0.6 85.6±0.3 0.0312 . Experiment 2 . . Control plants . Wind-treated plants . P-value . Fresh biomass, g 1.78±0.55 0.87±0.33 0.001 Dry biomass, g 0.23±0.06 0.12±0.04 0.001 Biomass ratio, % 86.7±0.6 85.6±0.3 0.0312 P-values are obtained from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=10) and experimental (n=10) groups. Open in new tab Table 1. Overview of the changes to the Arabidopsis biomass (mean ±SD) that were assessed after the end of the unidirectional wind treatment with a constant flow speed of 5 m s–1 in the second experiment . Experiment 2 . . Control plants . Wind-treated plants . P-value . Fresh biomass, g 1.78±0.55 0.87±0.33 0.001 Dry biomass, g 0.23±0.06 0.12±0.04 0.001 Biomass ratio, % 86.7±0.6 85.6±0.3 0.0312 . Experiment 2 . . Control plants . Wind-treated plants . P-value . Fresh biomass, g 1.78±0.55 0.87±0.33 0.001 Dry biomass, g 0.23±0.06 0.12±0.04 0.001 Biomass ratio, % 86.7±0.6 85.6±0.3 0.0312 P-values are obtained from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=10) and experimental (n=10) groups. Open in new tab Fig. 2. Open in new tabDownload slide Changes to the Arabidopsis stem segment diameter as a result of the unidirectional wind treatment with a constant flow speed of 5 m s–1 measured in the first experiment. Error bars represent the SD. A statistically significant difference (P≤0.05) from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=19) and experimental (n=21) groups is marked with (*). Fig. 2. Open in new tabDownload slide Changes to the Arabidopsis stem segment diameter as a result of the unidirectional wind treatment with a constant flow speed of 5 m s–1 measured in the first experiment. Error bars represent the SD. A statistically significant difference (P≤0.05) from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=19) and experimental (n=21) groups is marked with (*). Wind changes mechanical properties of Arabidopsis stems The primary inflorescence stems of Arabidopsis plants grown under constant wind were inclined in the direction of the wind but did not show any signs of mechanical damage. The mechanical properties, namely bending rigidity and Young’s modulus of elasticity, of segments taken from the tip and basal parts of the same stems were evaluated using the dynamic forced vibration method (Fig. 3). Wind treatment resulted in a significant increase (P<0.05) in Young’s modulus of elasticity of both tested segments (Fig. 3B). The average value of the elastic modulus of the bottom part of the stem of plants exposed to the wind was 1119 MPa, that is 17% higher compared with the untreated plants. The increase in the modulus of elasticity of the segments taken from the top part of the stem was >12% in the same stems. While the intensive property (E) of the stem material increased, its extensive property (EI) was only slightly (P>0.05) lower for all tested stem parts (Fig. 3A). Fig. 3. Open in new tabDownload slide Changes to the mechanical properties of Arabidopsis stem segments as a result of the unidirectional wind treatment with a constant flow speed of 5 m s–1 in the first experiment. (A) Bending rigidity. (B) Young’s modulus of elasticity. Error bars represent the SD. Statistically significant differences (P≤0.05) from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=19) and experimental (n=21) groups are marked with (*). Fig. 3. Open in new tabDownload slide Changes to the mechanical properties of Arabidopsis stem segments as a result of the unidirectional wind treatment with a constant flow speed of 5 m s–1 in the first experiment. (A) Bending rigidity. (B) Young’s modulus of elasticity. Error bars represent the SD. Statistically significant differences (P≤0.05) from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=19) and experimental (n=21) groups are marked with (*). Wind changes anatomical structure of Arabidopsis stems Exposure to wind induced substantial changes to the anatomical structure of Arabidopsis primary inflorescence stems in terms of their tissue organization (see Table 2; Fig. 4). Plant stems from the experimental group have significantly (P<0.05) more lignified interfascicular tissue compared with the control group in their bottom part. In addition, wind treatment resulted in a significant (P<0.05) decrease of the pith tissue area in the same part of Arabidopsis stems. On the other hand, the relative area of cortex together with epidermis was not affected by the wind treatment and remained almost the same in the bottom part of the stems in the experimental and control groups. The changes in the tissue organization in the top part of the primary inflorescence stems demonstrate the same trends as those observed in the bottom part as a result of exposure to wind (Table 2). Table 2. Contribution of tissues to the total cross-sectional area of the Arabidopsis primary inflorescence stem segments (mean ±SD) that was assessed after the end of the unidirectional wind treatment with a constant flow speed of 5 m s–1 in the second experiment. . Tissue contribution, % . . Control plants . Wind-treated plants . P-value . Bottom part of the stem Pith 38.92±3.33 31.64±3.23 <0.001 Lignified tissues 24.76±2.69 31.02±2.33 <0.001 Cortex+epidermis 36.43±3.06 37.34±3.6 0.68 Top part of the stem Pith 35.6±1.88 31.47±2.4 <0.01 Lignified tissues 22.99±1.83 26.21±1.08 <0.001 Cortex+epidermis 41.41±2.3 42.32±1.96 0.32 . Tissue contribution, % . . Control plants . Wind-treated plants . P-value . Bottom part of the stem Pith 38.92±3.33 31.64±3.23 <0.001 Lignified tissues 24.76±2.69 31.02±2.33 <0.001 Cortex+epidermis 36.43±3.06 37.34±3.6 0.68 Top part of the stem Pith 35.6±1.88 31.47±2.4 <0.01 Lignified tissues 22.99±1.83 26.21±1.08 <0.001 Cortex+epidermis 41.41±2.3 42.32±1.96 0.32 P-values are obtained from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=10) and experimental (n=10) groups. Open in new tab Table 2. Contribution of tissues to the total cross-sectional area of the Arabidopsis primary inflorescence stem segments (mean ±SD) that was assessed after the end of the unidirectional wind treatment with a constant flow speed of 5 m s–1 in the second experiment. . Tissue contribution, % . . Control plants . Wind-treated plants . P-value . Bottom part of the stem Pith 38.92±3.33 31.64±3.23 <0.001 Lignified tissues 24.76±2.69 31.02±2.33 <0.001 Cortex+epidermis 36.43±3.06 37.34±3.6 0.68 Top part of the stem Pith 35.6±1.88 31.47±2.4 <0.01 Lignified tissues 22.99±1.83 26.21±1.08 <0.001 Cortex+epidermis 41.41±2.3 42.32±1.96 0.32 . Tissue contribution, % . . Control plants . Wind-treated plants . P-value . Bottom part of the stem Pith 38.92±3.33 31.64±3.23 <0.001 Lignified tissues 24.76±2.69 31.02±2.33 <0.001 Cortex+epidermis 36.43±3.06 37.34±3.6 0.68 Top part of the stem Pith 35.6±1.88 31.47±2.4 <0.01 Lignified tissues 22.99±1.83 26.21±1.08 <0.001 Cortex+epidermis 41.41±2.3 42.32±1.96 0.32 P-values are obtained from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=10) and experimental (n=10) groups. Open in new tab Fig. 4. Open in new tabDownload slide Representative examples of the primary inflorescence stem cross-section showing anatomical tissue organization of its bottom part. (A) A plant from the control group. (B) A plant from the experimental group. co, cortex; ph, phloem, xy, xylem; if, interfascicular tissue; pi, pith. Fig. 4. Open in new tabDownload slide Representative examples of the primary inflorescence stem cross-section showing anatomical tissue organization of its bottom part. (A) A plant from the control group. (B) A plant from the experimental group. co, cortex; ph, phloem, xy, xylem; if, interfascicular tissue; pi, pith. Wind changes Ca2+ content of Arabidopsis stems Ion content measurements conducted after the second experiment showed that wind treatment resulted in a significant increase (P<0.001) in Ca2+ content in the Arabidopsis primary inflorescence stems (Fig. 5). The weight of calcium per gram of the fresh weight on average was almost twice higher in the stems of plants grown under constant unidirectional wind compared with the stems of control group plants. Fig. 5. Open in new tabDownload slide Changes to the Ca2+ content of Arabidopsis stems as a result of the unidirectional wind treatment with a constant flow speed of 5 m s–1 in the second experiment. Error bars represent the SD. A statistically significant difference (P≤0.05) from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=8) and experimental (n=8) groups is marked with (*). Fig. 5. Open in new tabDownload slide Changes to the Ca2+ content of Arabidopsis stems as a result of the unidirectional wind treatment with a constant flow speed of 5 m s–1 in the second experiment. Error bars represent the SD. A statistically significant difference (P≤0.05) from the two-sided Wilcoxon rank sum tests comparing medians of the corresponding parameters in the control (n=8) and experimental (n=8) groups is marked with (*). Discussion Morphological response of Arabidopsis As was shown in previous studies (Smith and Ennos, 2003; Anten et al., 2010), the effect of wind can differ considerably from the effect of mechanical perturbations in the same plants. Indeed, the changes to Arabidopsis Col-0 that were observed in this study differ from those reported for the same ecotype in previous investigations where wind influence was mimicked by mechanical perturbations. Regular brushing of Arabidopsis led to the reduction of the stem length by ~50% (Paul-Victor and Rowe, 2011), and a similar response was recorded as a result of physical touch (e.g. Braam and Davis, 1990). In contrast, in the present experiments, the highest observed decrease in the length of the primary inflorescence stem subjected to a constant wind was only 14% compared with the untreated plants. These observations are consistent with those reported by Bossdorf and Pigliucci (2009) where the average reduction of the plant height of various natural populations of Arabidopsis was ~13.2% when subjected to a periodic wind treatment. In addition to the inhibition of the stem length, a common thigmomorphogenetic response in many plants includes an increase in the stem diameter. This was reported for numerous plants as a result of mechanical bending (see, for example, Goodman and Ennos, 1996; Telewski, 2006; Coutand et al., 2010). However, the present results show that the mean diameter of the primary inflorescence stem measured for its bottom and top parts was reduced in the wind-exposed plants compared with the control group. Lower stem diameter was also reported in trees as a result of wind influence. For example, exposure of Cecropia schreberiana to the natural wind environment resulted in significantly lower stem diameters in wind-exposed plants compared with those in plants sheltered from the wind (Cordero, 1999). Slightly lower stem diameter was also observed in lodgepole pine (Pinus contorta Douglas ex Louden) subjected to a constant wind in a controlled wind tunnel environment (Rees and Grace, 1980). In addition, the influence of wind, without mechanical flexure, led to a decrease in the stem diameter of sunflowers (Helianthus annuus L.) in factorial experiments conducted by Smith and Ennos (2003). When both wind and flexure were combined, a slight increase in the stem diameter was observed; however, as pointed out by the authors, the amount of mechanical flexure received by plants in this group was considerably higher than the wind could create. Interestingly, a reduction of the stem diameter in Arabidopsis Col-0 was also reported as a result of brushing (Paul-Victor and Rowe, 2011), showing, in this respect, similarities of the response to the wind and brushing in these plants. We found that plants grown under constant unidirectional wind had a significantly lower number of stems and branches compared with the untreated plants. As will be discussed below, this can be a part of the acclimation strategy of Arabidopsis to deal with wind loadings. The reduced branching in Arabidopsis was also reported as a result of a periodic wind exposure of different flow speeds (Bossdorf and Pigliucci, 2009), but not for all 17 tested natural populations. The same behaviour was reported earlier by Pigliucci (2002) for 11 natural accessions of Arabidopsis that were subjected to a periodic wind treatment of different durations. While the number of branches in some accessions decreased, a similar or even increased number was observed in others. On the other hand, increased branching was reported for Potentilla reptans L. as a response to the mechanical brushing that was applied to mimic a wind environment (Liu et al., 2007). Another effect of mechanical perturbations on plants is the decrease of aboveground biomass (Niklas, 1998; Kern et al., 2005). This can be linked to the overall reduction of the plant’s size as a result of thigmomorphogenesis. In the present study, both fresh and dry aboveground biomass was reduced for plants grown under a constant unidirectional wind. This is attributed to the changes in the Arabidopsis morphology where a lower number of stems and branches together with slightly shorter stems of reduced diameter were observed in plants subjected to wind. The decrease of Arabidopsis dry biomass as a result of wind treatment is consistent with previous observations by Bossdorf and Pigliucci (2009). Although changes in the biomass were not quantified for Arabidopsis subjected to mechanical perturbations in the studies by Braam and Davis (1990) and Paul-Victor and Rowe (2011), it can be reasonably presumed that it was decreased due to the significant reduction in size of the plants. The very close values of the biomass ratio in both experimental and control groups in the present study point to the same amount of water in both groups at the time of harvest and throughout the experiments. Thus, the changes observed as a result of wind treatment were not due to the water loss in plants from the experimental group through increased evaporation. In addition, a similar water content can be associated with water-saving strategies of plants under wind, but further investigation of this aspect is required. Comparing the changes in Arabidopsis morphology, some similarities between responses to wind and mechanical brushing can be noted. In both cases, a reduction of the plant biomass and decrease in the stem diameter are observed, even though the latter is not a common response to mechanical bending in plants. However, the inhibition of the stem length is much lower in wind-exposed plants compared with those subjected to brushing. The observed differences in the responses to constant unidirectional wind as in the current study and mechanical contact (e.g. Paul-Victor and Rowe, 2011) can be attributed to the fact that in the first case Arabidopsis can adapt to the constant stress coming from a single direction by adapting its shape and structure, while it is not possible to achieve this when stress is applied from multiple directions, as in the case of brushing. Anemotropic response of Arabidopsis to a constant unidirectional wind Environmental stimuli have an effect on the specific orientation of plant growth, which is known as tropism. A tropic response can be either positive, towards the stimulus, or negative, away from it. The response of plants to touch and other mechanical contacts is known as thigmotropism. By analogy, the response of plants to wind can be termed as anemotropic or anemotropism. In the present experiments, Arabidopsis ecotype Col-0 grown under the constant unidirectional wind exhibited an anemotropic response (Fig. 6). The young seedlings demonstrated a positive anemotropic response to wind, by directing their primary growth in the direction opposite to the direction of the flow (Fig. 6A, B). To the best of our knowledge, this is the first time an anemotropic response to a unidirectional wind has been documented in any plant system (Telewski, 2012), although previous work on conifers already suggested the existence of this type of tropic response (Rees and Grace, 1980; Berthier and Stokes, 2006). As Arabidopsis developed under the wind and its size increased, the shape of the plants became windswept; however, the upwind bending of the stems was preserved (Fig. 6C, D). The windswept growth form is widely found in trees for which it is a crucial acclimation response to the wind environment (Telewski, 2012). It should be noted that the Arabidopsis stem is known to exhibit gravitropism when inclined at an angle from the vertical orientation. In the case of the gravitropic response, the stem returns back to the vertical orientation within a few hours (Fukaki et al., 1996). Curvature of Arabidopsis stems grown under constant unidirectional wind was preserved over time (see Fig. 6), suggesting that the observed response is mainly due to anemotropism. However, an interaction between anemotropic and gravitropic responses cannot be fully excluded since gravity was inevitably present in the experiments. As was shown in the studies where Arabidopsis was grown in a centrifuge (e.g. Dümmer et al., 2015; Chauvet et al., 2016), the combination of gravity with an additional force results in a growth response in the direction parallel to their resultant force. In the present study, the additional force was exerted by the wind, which could explain the observed curvature of the stem and the fact that Arabidopsis grown under constant wind did not develop parallel to the wind direction. Fig. 6. Open in new tabDownload slide Arabidopsis ecotype Col-0 grown under the constant unidirectional wind exhibits positive anemotropic response. (A) Young Arabidopsis seedlings (30 DAS) from experimental and control groups. (B) Young Arabidopsis seedlings (30 DAS) inside the wind tunnel test section. (C) Arabidopsis plants (34 DAS) from experimental and control groups. (D) Arabidopsis plants (34 DAS) inside the wind tunnel test section. Note that in (A) and (C) plants from the experimental group were removed from the wind tunnel and the curvature of their stems is increased compared with plants in (B) and (D) where Arabidopsis is subjected to a constant unidirectional wind of 5 m s–1. For reference, in all parts of the figure, the diameter of the pot is 76 mm. Fig. 6. Open in new tabDownload slide Arabidopsis ecotype Col-0 grown under the constant unidirectional wind exhibits positive anemotropic response. (A) Young Arabidopsis seedlings (30 DAS) from experimental and control groups. (B) Young Arabidopsis seedlings (30 DAS) inside the wind tunnel test section. (C) Arabidopsis plants (34 DAS) from experimental and control groups. (D) Arabidopsis plants (34 DAS) inside the wind tunnel test section. Note that in (A) and (C) plants from the experimental group were removed from the wind tunnel and the curvature of their stems is increased compared with plants in (B) and (D) where Arabidopsis is subjected to a constant unidirectional wind of 5 m s–1. For reference, in all parts of the figure, the diameter of the pot is 76 mm. Acclimation of Arabidopsis to a constant unidirectional wind To grow and survive in windy environments, plants have developed a number of acclimation strategies. These strategies include streamlining and reconfiguration, damping, and wind-induced pruning (Gardiner et al., 2016). Reconfiguration, the term introduced by Vogel (1984) to describe the change of plant shape under wind, and streamlining are common for most plants regardless of size and growing environment. In terms of this strategy, plants reduce their frontal area and aerodynamically optimize their shape to experience less force from the wind. The details of the physics and mechanics behind streamlining and reconfiguration can be found in, for example, Gosselin (2019). Plants mainly experience force from the wind in the form of fluid dynamic drag, which is defined as: D=12ρACDU∞2(3) where ρ is the density of the fluid, A the frontal area of the plant, CD the drag coefficient, and U∞ flow velocity. For plants, it was shown that drag does not scale as U2 but rather as U2+ν, where ν is the Vogel exponent (Vogel, 1984, 1989). In order to reduce the drag force experienced from wind, plants can modify only two parameters in Equation 3, namely their drag coefficient and frontal area. In the present study, Arabidopsis is expected to exhibit a long-term acclimation strategy to a unidirectional wind environment. As mentioned above, Arabidopsis grown inside the wind tunnel developed in the downstream direction and its shape became windswept. In trees, a windswept form is a result of long-term streamlining that occurs as a response to regular wind exposure. Trees with windswept crowns are known to experience substantially less drag (Telewski and Jaffe, 1986a); that is, values of their CD in Equation 3 are reduced. Taking into account similarity in the long-term response to continuous wind, it can be presumed that Arabidopsis optimized its shape into a more streamlined one and thus experienced less drag. In addition, phenotyping showed a significantly lower total number of branches (including basal branches) in the wind-exposed plants. This in turn decreased their frontal area compared with the untreated plants that had more branches and stems. From Equation 3, a reduction in the frontal area directly leads to a decrease in the drag force the plant experiences from the wind. Hence, the reduced number of stems and branches in the experimental group compared with the control group can be considered as part of the long-term acclimation strategy of Arabidopsis Col-0 to constant unidirectional wind. Changes in the mechanical properties of Arabidopsis stems The observed changes to the mechanical properties of Arabidopsis are opposite to those reported as a result of brushing, where bending rigidity and Young’s modulus of elasticity of inflorescence stems were significantly reduced (Paul-Victor and Rowe, 2011). In the present study, only a marginal decrease in the bending rigidity of Arabidopsis stems was recorded for the experimental group (Fig. 3A). It should be noted that this property is dependent on the stem geometry, namely the second moment of area. This parameter, in turn, is a function of the stem diameter, which was lowered as a result of the wind treatment (Fig. 2). As was discussed earlier, plants experience a drag force from the wind that is dependent on the characteristic dimension of the plant (projected frontal area). Consequently, the reduced stem diameter is also important for reducing the wind-induced drag force. Paul-Victor and Rowe (2011) suggest that changes in mechanical properties are related to changes in the developmental rate and, combined with alterations in plant morphology, are adaptive to the growth environment. Therefore, a possible explanation for the contrasting results between the two types of treatment may be the fact that under unidirectional wind Arabidopsis did not bend in opposite directions as in the case of brushing, and hence increased flexibility was not required to adapt to the growth environment. On the other hand, wind treatment increased the modulus of elasticity of the primary inflorescence stems of Arabidopsis (Fig. 3B). A higher elastic modulus means that a larger stress needs to be applied in order to produce the same strain (deformation). This may also form a part of the acclimation strategy, making the plant material more rigid so it can withstand the loads from the continuous wind exposure. In addition, an increased modulus of elasticity compensates the influence of lower stem diameter on the bending rigidity, so stems sway less in the wind compared with the case where both E and D are reduced. Other studies where the influence of different types of perturbations (wind, flexing, rubbing, etc.) on the mechanical properties of plants was assessed show that the changes can be in any direction. Bending rigidity of stems was reported to decrease (e.g. Telewski and Jaffe, 1986b; Cordero, 1999), increase (e.g. Hepworth and Vincent, 1999; Kern et al., 2005; Niez et al., 2019), or remain unaffected (e.g. Jaffe et al., 1984). Young’s modulus of elasticity also can increase (e.g. Telewski and Jaffe, 1986a; Gladala-Kostarz et al., 2020) or decrease (e.g. Jaffe et al., 1984; Cordero, 1999; Kern et al., 2005) as a result of various mechanical treatments including wind. The present results support the hypothesis proposed by Newcombe (1895) that there is no universal change in the mechanical properties of plants as a response to mechanical stress (for a review, see Telewski, 2016). The changes are likely to adjust to the exact type of perturbation and depend on many factors, such as frequency of perturbations, amount of stress induced per perturbation, direction of perturbation, etc. Thus, as discussed in Coutand et al. (2000), it is important to characterize perturbations experienced by plants as well as their growth environment. In the present study, the wind conditions inside the test section were characterized using hot-wire anemometry and it was ensured that other environmental variables were the same for both groups. Experiments conducted at different times of the year (see the Materials and methods) confirmed that changes to the mechanical properties of Arabidopsis primary inflorescence stems resulting from continuous exposure to wind at a constant flow speed of 5 m s–1 are repeatable. In addition, as was shown for loblolly pines (Telewski and Jaffe, 1986b) and hybrid poplars (Pruyn et al., 2000), the response to mechanical perturbations depends on the plant genotype. In future studies, various Arabidopsis ecotypes and mutants can be subjected to different wind speeds, and the corresponding changes to their mechanical as well as morphological properties can be quantified. This will give the possibility to assess how Arabidopsis adapts to different wind conditions and how these conditions affect the aforementioned properties. Changes in the stem anatomy and ion content related to the changes in the mechanical properties Lignin is known to strengthen cell walls and supportive fibres, and thus provides rigidity to plants (Smith et al., 2013; Brulé et al., 2016). As was shown with the lignin deficit Arabidopsis mutants, irx4, reduction of lignin leads to the decrease in the mechanical properties of Arabidopsis stems (Jones et al., 2001). Consequently, the observed changes in the relative areas of structural tissues as a result of wind influence in the present study suggest direct correlation between an increase in the area of the lignified tissues and an increase in the modulus of elasticity of the tested stem segments. The larger relative area of lignified tissues in Arabidopsis stems observed in wind-exposed plants is opposite to the effects of mechanical perturbations in the form of brushing. Paul-Victor and Rowe (2011) reported a decrease in this parameter in the stems of brushed plants. This was partially attributed to the recorded reduction in the mechanical properties of perturbed plants compared with the control group. Ko et al. (2004) showed that lignification in Arabidopsis inflorescence stems is related to their weight and length. Furthermore, it was found that an artificial increase of stem weight promoted further formation of lignified tissues. As in the experiments by Ko et al. (2004), where addition of the weight to the stem tip increased the gravitational force exerted on Arabidopsis stems, in the present study, stems were also made to experience an additional force, namely the drag force that was induced by the constant unidirectional wind. This suggests a possible explanation for the observed increase of the lignified tissues in the wind-treated plants compared with the control group. In addition to an increase in the area of lignified tissues, stems of wind-exposed plants had a higher Ca2+ content. An increase in Ca2+ is known to occur in response to different types of mechanical stress in plants (Telewski, 2006). Furthermore, Ca2+ ions contribute to cell wall stiffening by taking part in the formation of pectate gels (Jiang et al., 2005; Höfte et al., 2012). Based on this, it can be presumed that elevated levels of Ca2+ may also contribute to the increased modulus of elasticity of plant stems from the experimental group. Wind and water stress in plants In general, it can be expected that wind leads to water stress in plants through an increase in transpiration from plant surfaces. In many cases, the increased evaporation from plants in wind is a result of the decrease in cuticle resistance which occurs through abrasive wear and damage due to flexing of leaves and collisions with other leaves (Jones, 2013). This was experimentally shown for a number of plants, such as Festuca arundinacea (Grace, 1974), Picea sitchensis, and Pinus sylvestris (Van Gardingen et al., 1991). However, several theoretical and experimental studies show that, in certain cases, wind has a small influence on the evaporation rate in plants and even a decrease in transpiration has been observed (Monteith, 1965; Drake et al., 1970; Rees and Grace, 1980; Dixon and Grace, 1984). It should be noted that Rees and Grace (1980) and Dixon and Grace (1984) conducted experiments in a wind tunnel and their findings thus are directly relevant to the current study. The present study focuses on the changes in the Arabidopsis morphology and mechanical properties as a result of continuous unidirectional wind treatment at a constant speed. The growth conditions between the control and experimental groups were identical except for the wind treatment. Moreover, the wind environment was created in a purpose-built wind tunnel, that was precisely characterized, and through repeated experiments the results were shown to be reproducible. Any changes in the plant microclimate came directly from the wind and are expected to occur in the natural environment under the same conditions, resulting in similar changes to the plant structure and mechanical properties. The top edges of the plant pots were in line with the wind tunnel floor, hence the leaf rosettes were located very close to the wind tunnel floor inside the boundary layer, where flow speed is significantly reduced. Consequently, the disturbance from wind to the leaf rosettes of Arabidopsis was reduced to a minimum throughout the experiments and neither flexing nor rubbing of leaves against each other was observed. The other aboveground parts of Arabidopsis swayed in the wind but did not touch parts of neighbouring plants or other parts of the same plant. Based on this, it can be presumed that damage to the cuticle was also reduced or even eliminated, thus avoiding an increase in transpiration from the plants through a decrease in the cuticle resistance. Conclusions In this study, Arabidopsis ecotype Col-0 was subjected to a continuous wind treatment in a purpose-built wind tunnel. Exposure to wind resulted in a positive anemotropic response, recorded for the first time in any plant system, and in pronounced changes to the plant structure. In addition, mechanical properties, anatomical tissue organization, and ion content of the primary inflorescence stems were modified. Overall, the observed changes can be interpreted as a part of the acclimation strategy of Arabidopsis to wind. Supplementary data The following supplementary data are available at JXB online. Fig. S1. Wind tunnel design. (A) CAD model. (B) Wind tunnel inside the glasshouse. Fig. S2. Representative examples of the mean velocity contours at several locations along the test section length for three settings of the variable transformer. Acknowledgements This work was supported by the University of Glasgow’s Lord Kelvin/Adam Smith (LKAS) PhD Scholarship. Hot-wire anemometry instrumentation used in this study was provided by the National Wind Tunnel Facility funded by Engineering and Physical Sciences Research Council United Kingdom, grant no. EP/L024888/1. We would like to thank Amparo Ruiz-Prado for help with growing plants, and Naomi Donald for help with flame photometry tests. Author contributions OZ: conceptualization, investigation, formal analysis, visualization, writing—original draft, writing—review and editing. MRB: conceptualization, supervision, resources. HZB: conceptualization, supervision. AB: conceptualization, supervision, writing—review and editing. Data availability The data supporting the findings of this study are available from the corresponding author, Oleksandr Zhdanov, upon request. References Allen MR , Dube OP, Solecki W, et al. 2018 . Framing and context . In: Masson-Delmotte V, Zhai P, Pörtener H-O, et al. ., eds. Global Warming of 1.5 ° C. 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TI - Wind-evoked anemotropism affects the morphology and mechanical properties of Arabidopsis
JF - Journal of Experimental Botany
DO - 10.1093/jxb/eraa541
DA - 2021-02-27
UR - https://www.deepdyve.com/lp/oxford-university-press/wind-evoked-anemotropism-affects-the-morphology-and-mechanical-8MZOTJ3Aa8
SP - 1906
EP - 1918
VL - 72
IS - 5
DP - DeepDyve
ER -