Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Ultraviolet‐B exposure leads to up‐regulation of senescence‐associated genes in Arabidopsis thaliana

Ultraviolet‐B exposure leads to up‐regulation of senescence‐associated genes in Arabidopsis thaliana Abstract Exposure to UV‐B radiation resulted in a loss of chlorophyll and an increase in lipid damage in a similar manner to that induced during natural senescence. In addition, exposure to UV‐B led to the induction of a number of genes associated with senescence (SAG12, 13, 14, and 17). These results show, for the first time, that exposure to UV‐B can lead to cellular decline through active and regulated processes involving many genes also associated with natural senescence. Arabidopsis, photosynthetic genes, senescence associated genes, ultraviolet‐B radiation. PAGs, photosynthesis‐associated genes, SAGs, senescence‐associated genes, UV‐B, ultraviolet‐B radiation Introduction Persistent depletion of the stratospheric ozone layer is continuing to result in increases in the levels of ultraviolet‐B radiation (UV‐B: 280–320 nm) reaching the Earth's surface (Mckenzie et al., 1999; Zerefos et al., 1997). UV‐B radiation is biologically very active and exposure to both artificial high (control environment), as well as realistic (field experiments), levels has been shown to lead to changes in plant growth and development as well as result in profound changes in gene expression (for review see Strid et al., 1994; Jordan, 1996). There is, however, considerable developmental variation in sensitivity to UV‐B radiation. In both Arabidopsis and pea, older leaves were found to become damaged by UV‐B faster and to a greater extent than younger leaves or organs (Lois, 1994; A‐H‐Mackerness et al., 1998; Jordan et al., 1998). Exposure was found to lead to an initial phase of chlorophyll loss followed by desiccation of the tissue. At the biochemical level, the rate of photosynthesis is greatly reduced in these leaves, primarily as a result of a decline in RUBISCO protein levels and disruption to the chloroplast membranes. Recent studies have shown that some of these changes can be attributed partially to effects of UV‐B on expression of genes encoding key photosynthetic proteins (Strid et al., 1994; A‐H‐Mackerness and Jordan, 1999). Thus, in leaves at a certain stage of development, exposure can induce changes at the physiological, biochemical and molecular levels that resemble symptoms identified in plants undergoing senescence. Senescence in plants is highly organized and appears to involve not only the breakdown of macromolecules such as proteins and lipids, but also further catabolism/ anabolism of these molecules into forms for transport and retrieval by the rest of the plant (for reviews see Smart, 1994; Noodén et al., 1997). A decline in photosynthesis and a loss of chlorophyll are early symptoms of senescence, with chloroplasts one of the primary targets for degradation (Thomas and Stoddart, 1980; Grove and Mohanty, 1992). Although the actual processes involved in senescence of photosynthetic tissue have been characterized in a number of plant species, the regulatory mechanisms that govern the timing of leaf senescence remains elusive. However, senescence is thought to be under genetic control and recent studies have shown that differential expression of specific genes is associated with the senescence syndrome (for reviews see Buchanan‐Wollaston, 1997; Weaver et al., 1997). During leaf senescence transcripts for key photosynthetic proteins decline (Bate et al., 1991; Hensel et al., 1993). In addition, expression of a variety of genes is induced, including those represented by the SAG clones identified from naturally senescing Arabidopsis leaves (Lohman et al., 1994). A number of these senescence‐associated genes have been cloned and sequenced. Among these identified clones are genes encoding proteases (SAG12), glutamine synthase (Atgsr2), ACC synthase (ACS6), lipases, glyoxylate cycle enzymes, and polyubiquitin which may be involved in protein degradation and nitrogen remobilization. Others, which encode for metal‐binding proteins (SAG14), metallothionein (SAG17), catalase (LSC650), and cytochrome P450, likely function to scavenge and detoxify reactive oxygen species (Buchanan‐Wollaston, 1997; Weaver et al., 1997). There are also a number of isolated SAG cDNA clones that have no obvious senescence‐related function and many others still remain unidentified. Leaf senescence progresses in an age‐dependent manner, but both endogenous and exogenous factors can greatly influence the timing of this process. Thus, phytohormones, shading, temperature, and oxidative stresses, such as pathogen infection and ozone treatment, can all lead to premature senescence of the tissue (Smart, 1994; Gan and Amasino, 1997). UV‐B exposure has been shown to lead to the generation of reactive oxygen species (ROS) (Arnott and Murphy, 1991; Green and Fluhr, 1995; Dai et al., 1997) and a number of studies have highlighted the similarities between responses to UV‐B and other oxidative stresses including pathogen infection and ozone treatment (see A‐H‐Mackerness, 2000, and references within). However, despite the extensive work carried out in the last two decades, relatively little is known about the mechanisms by which higher plants perceive UV‐B radiation and the processes that are involved in initiating the physiological responses to this stress. Therefore, in order to determine the nature of cell death induced by UV‐B, a number of physiological, biochemical and molecular processes involved in UV‐B induced responses in older leaves of Arabidopsis and those brought about through natural senescence have been characterized and compared in this study. Materials and methods Plant material, experimental conditions and feeding experiments Arabidopsis thaliana (Columbia (MGH)) was used in all experiments. Seeds were treated for 3 d at 4 °C after sowing on a compost:sand:vermiculite mixture and then transferred to a Sanyo phytotron with 12 h light (22 °C), 12 h dark (16 °C) cycles at 70% humidity. At 14 d the seedlings were transplanted into individual pots and grown for a further 14 d. Incident irradiation was provided by Philips warm white fluorescent tubes giving a fluence rate of 150 μmol m−2 s−1 photosynthetically active radiation (400–700 nm). Half the plants were then given supplementary UV‐B radiation from four UV lamps (Philips TL 12, 40 W) during the photoperiod. The fluence rate between 280 and 320 was 3.2 μmol m−2 s−1. The UV lamps were covered with cellulose acetate sheets, which were changed daily, to exclude UV radiation below 290 nm. The plants in the other cabinet (controls) were subjected to the same treatment, but the UV lamps were covered with Mylar film to exclude radiation below 320 nm. Each experiment was repeated at least three times with similar results. For the UV‐B experiments, the outer older rosette leaves or the inner three whorls of the younger leaves were taken at random from plants in different parts of the cabinets, 6 h into each photoperiod (unless otherwise stated) and at least three plants were used per sample for analysis. For the naturally senescent leaves, the lower rosette leaves were taken from at least five plants grown for 4 weeks (MG, mature green), 5 weeks (S1, early senescence) and 8 weeks (S2, mid‐senescence showing signs of yellowing) in the absence of UV‐B or UV‐A. Purification of total RNA, northern blotting and hybridization Total RNA was extracted from Arabidopsis leaves (0.5 g) as described previously (Jordan et al., 1998). RNA analysis, blotting, prehybridization, hybridization, washes, and autoradiography were as described earlier (A‐H‐Mackerness et al., 1999). The Lhcb, psbA, PR‐1, and PDF1.2 cDNA probes were described earlier (A‐H‐Mackerness et al., 1999). The cDNA for the SAG genes SAG12, 13, 14 and 17 are described previously (Lohman et al., 1994). The blots presented are representative of three or more independent experiments. Relative amounts of radioactivity bound to specific bands were quantified using a Phosphorimager SI (Molecular Dynamics Ltd, Bucks, UK). Loading control analysis of each blot was carried out by hybridization using an 18S rRNA probe from pea (see Surplus et al., 1998, for details). The data are presented, from the UV‐B experiments, as percentage transcript levels in UV‐B‐treated plants as compared to plants treated under control conditions and from the senescence experiments, as percentage transcript levels in S1 or S2 leaves compared with levels in MG leaves. Lipid peroxide (malondialdehyde) and chlorophyll quantification The lipid peroxidation (MDA) assays were carried out as described earlier (A‐H‐Mackerness et al., 1998). Chlorophyll (Chl) analysis was carried out with approximately 0.5 g of leaf tissue and using the method described earlier (Jordan et al., 1998). Measurement of PS II Chl fluorescence (Fv/Fm) Chl fluorescence was determined by using a Hansatech plant efficiency analyser (Hansatech, Kings Lynn, UK). The leaves were dark adapted for 5 min prior to measurement for 30 s as previously described (Jordan et al., 1998). Statistical analysis A factorial analysis of variance (ANOVA) was performed for the chlorophyll, MDA and Fv/Fm values. Standard errors of the differences of the means (SED) were determined from the ANOVA. Results and discussion The effects of UV‐B radiation on plants have been extensively studied in a large number of plant species (A‐H‐Mackerness and Jordan, 1999). However, because UV‐B is high‐energy radiation and absorbed by all macromolecules, it is still unclear which responses to UV‐B are specific and mediated through receptors and which are due to non‐specific damage. The response to UV‐B depends heavily on a number of parameters including the developmental stage of tissue studied (for further discussion see A‐H‐Mackerness and Jordan, 1999). Although a small number of studies have tried to address the mechanism behind developmental variation in sensitivity to UV‐B, little has been done to determine the process by which older leaves deteriorate due to exposure to UV‐B. Consequently, the effects of UV‐B on a number of biochemical and molecular markers of senescence were determined in the lower rosette leaves of Arabidopsis plants. These leaves were showing signs of chlorosis by the third day of UV‐B treatment (data not shown). The older, outer leaves treated with supplementary UV‐B showed signs of premature senescence, with a loss of chlorophyll and increases in membrane degradation in a manner similar to the effects detected in naturally senescent leaves (Fig. 1a, b). In contrast, no significant change in either parameter was observed in plants treated under control conditions. Previous studies have indicated that chlorophyll loss does occur in the outer leaves, but not the younger inner leaves, of Arabidopsis plants exposed to supplementary UV‐B (Jordan et al., 1998) and similar declines have been reported for senescent leaves (Hensel et al., 1993; Lohman et al., 1994). Degradation of membranes and a decline in the level of lipids in senescent tissue has been reported (Thompson et al., 1997) and increases in levels of MDA, indicating lipid peroxidation, have been found during senescence (Dhindsa and Dhindsa, 1981). Similarly, a rise in MDA levels has been shown to occur in response to UV‐B exposure in a number of plant species (Arnott and Murphy, 1991; Dai et al., 1997; A‐H‐Mackerness et al., 1998). In contrast to similar patterns of change in lipid and chlorophyll levels in both leaves treated with UV‐B and undergoing natural senescence, the maximum quantum efficiency of PSII photochemisty (Fv/Fm) was not affected in naturally senescent leaves, while levels significantly fell in leaves treated with UV‐B (Fig. 1c). These observations are in accordance with recent studies carried out on whole plants. Fv/Fm has been shown to be only slightly affected as leaves senesce even though a substantial decrease in the chlorophyll content occurs (Lu and Zhang, 1998). In contrast, PSII has been identified as one of the most UV‐B labile components of the photosynthetic system and thus dramatic losses of PSII efficiency have been reported in a variety of plant species exposed to supplementary UV‐B radiation (see Jordan, 1996, and references within). Profound changes in gene expression have been reported in leaves undergoing natural senescence (Buchanan‐Wollaston, 1997; Weaver et al., 1997) as well as in leaves treated with supplementary UV‐B (Strid et al., 1994; A‐H‐Mackerness, 2000). Thus the possibility that the same genes are regulated in the two sets of responses was investigated. In the outer older leaves UV‐B exposure resulted in a decline in both photosynthetic associated genes (PAGs), Lhcb and psbA, after 1 d with levels continuing to fall during subsequent days. A similar decline in transcripts was also detected in leaves undergoing senescence (Fig. 2a). Decline in these transcripts has been reported previously in naturally senescent leaves (Lohman et al., 1994) and within the same time scale of this study in the older outer, but not younger inner, leaves treated with UV‐B (Jordan et al., 1998). Falls in RbcS and rbcL transcripts, and the subsequent decline in RUBISCO level and activity, in UV‐B treated (A‐H‐Mackerness et al., 1997) and senescent tissues (Bate et al., 1991; Hensel et al. 1993) have also been reported. Transcripts for two pathogen‐related proteins, PR‐1 and PDF1.2, increased in response to UV‐B exposure and during senescence (Fig. 2b). Transcripts of PR‐1 have been shown previously to rise in response to pathogen infection, ozone and UV‐B treatment as well as during senescence (Green and Fluhr, 1995; Buchanan‐Wollaston, 1997; Sharma et al., 1996; Surplus et al., 1998). A number of senescence‐associated genes (SAGs) have been catalogued from naturally senescing Arabidopsis leaves (Lohman et al., 1994). Unlike the effect of UV‐B on PAGs and PR protein expression, no work has been carried out to determine the effect of UV‐B on these molecular markers of senescence. The level of SAG13, which encodes a short chain alcohol dehydrogenase, and SAG14, which encodes a blue copper‐binding protein, both increased in the outer leaves on exposure to UV‐B after just 1 d of UV‐B treatment and continued to increase (Fig. 2c). Similarly, Brosche and Strid have shown that transcripts encoding for another alcohol dehydrogenase increases on exposure to UV‐B radiation (Brosche and Strid, 1999), but as in senescence, the exact function of this enzyme in tolerance/defence against UV‐B is unclear. Levels of both SAG13 and 14 were also induced by ozone treatment (Miller et al., 1999) and thus it is possible that these proteins play a role in oxidative stress responses rather than having a specific or unique role during senescence. The slow induction of these transcripts in inner, young leaves, and the high levels in outer leaves as compared to senescing leaves also further indicates a function more related to stress than directly in senescence (Fig. 2). Expression of the metallothionein gene, SAG17, was also induced in outer and, to a much lesser extent, in inner leaves by exposure to supplementary UV‐B (Figs 2c, 3). Interestingly, SAG17 was not induced by exposure to the oxidative stress ozone (Miller et al., 1999), although increases in naturally senescing tissue have been reported extensively (Lohman et al., 1994; Weaver et al., 1997). Similarly, transcripts encoding SAG12, which encodes a cysteine protease, rose during senescence (Fig. 2c; Lohman et al., 1994; Noh and Amasino, 1999) and only in outer leaves after 3 d of UV‐B exposure (Fig. 2c), but not in inner leaves (Fig. 2), after ozone treatment (Miller et al., 1999) or pathogen infection (Pontier et al., 1999). Unlike the expression levels of the other SAGs which were either lower or comparable in senescent and outer leaves treated with UV‐B, the transcript levels of SAG12 were significantly higher in S2 leaves than in the UV‐B treated leaves. SAG12 is one of the few genes identified to date where expression is closely linked to senescence and is not increased by many other stress treatments (Gan and Amasino, 1997; Weaver et al., 1997; Noh and Amasino, 1999). Thus the difference in SAG12 levels in the outer UV‐B‐treated leaves and the S2 leaves is likely due to comparison of tissue at different ‘stages’ of senescence. Fig. 1. View largeDownload slide Quantitative changes in (a) chlorophyll, (b) lipid peroxide (MDA) and (c) chl fluorescence (Fv/Fm) in UV‐B treated outer older and naturally senescent leaves of Arabidopsis thaliana. Measurements were taken from the outer leaves of 4‐week‐old plants which were treated with or without UV‐B for 1, 2 and 3 d or from leaves of plants left to senesce naturally (MG, mature green; S1, early senescence; S2, mid‐senescence showing signs of yellowing). For the UV‐B experiments, the outer rosette leaves were taken at random from plants in different parts of the cabinets, 6 h into each photoperiod and at least three plants were used per sample for analysis. For the senescence experiments, the lower rosette leaves were taken from at least five plants grown for 4 weeks (MG), 5 weeks (S1) and 8 weeks (S2) in the absence of UV‐B or UV‐A. Each point is an average of three independent experiments and the error bars indicate the standard error of the differences of the means (SED). Fig. 1. View largeDownload slide Quantitative changes in (a) chlorophyll, (b) lipid peroxide (MDA) and (c) chl fluorescence (Fv/Fm) in UV‐B treated outer older and naturally senescent leaves of Arabidopsis thaliana. Measurements were taken from the outer leaves of 4‐week‐old plants which were treated with or without UV‐B for 1, 2 and 3 d or from leaves of plants left to senesce naturally (MG, mature green; S1, early senescence; S2, mid‐senescence showing signs of yellowing). For the UV‐B experiments, the outer rosette leaves were taken at random from plants in different parts of the cabinets, 6 h into each photoperiod and at least three plants were used per sample for analysis. For the senescence experiments, the lower rosette leaves were taken from at least five plants grown for 4 weeks (MG), 5 weeks (S1) and 8 weeks (S2) in the absence of UV‐B or UV‐A. Each point is an average of three independent experiments and the error bars indicate the standard error of the differences of the means (SED). Fig. 2. View largeDownload slide Transcripts levels in wild‐type Arabidopsis plants exposed to supplementary UV‐B or left to senesce naturally (for details see Materials and methods). (i) Northern blot analysis showing transcripts of (a) photosynthetic genes, (b) defence‐associated genes and (c) senescence‐associated genes in UV‐B‐treated and naturally senescing leaves. RNA was extracted from the outer leaves of 4‐week‐old plants which were treated with (UV) or without (C) supplementary UV‐B radiation for 1, 2 and 3 d or from leaves of plants left to senesce naturally (for further details see Fig. 1 legend). The blots shown are representative of results obtained from three separate independent experiments. Fig. 2. View largeDownload slide Transcripts levels in wild‐type Arabidopsis plants exposed to supplementary UV‐B or left to senesce naturally (for details see Materials and methods). (i) Northern blot analysis showing transcripts of (a) photosynthetic genes, (b) defence‐associated genes and (c) senescence‐associated genes in UV‐B‐treated and naturally senescing leaves. RNA was extracted from the outer leaves of 4‐week‐old plants which were treated with (UV) or without (C) supplementary UV‐B radiation for 1, 2 and 3 d or from leaves of plants left to senesce naturally (for further details see Fig. 1 legend). The blots shown are representative of results obtained from three separate independent experiments. Fig. 3. View largeDownload slide Quantitative changes in SAG12, 13, 14, and 17 transcript levels from inner younger and outer older leaves of plants treated with supplementary UV‐B or from leaves left to naturally senesce. The amount of hybridized radioactivity was quantified using a phosphorimager; the data shown have been corrected for loading differences by using the counts obtained with 18S rRNA. The data are presented, from the UV‐B experiments, as percentage transcript levels in UV‐B‐treated plants as compared to control plants and from the senescence experiments, as percentage transcript levels in S1 or S2 compared with levels in MG leaves. Values are means±SE of three independent experiments. Fig. 3. View largeDownload slide Quantitative changes in SAG12, 13, 14, and 17 transcript levels from inner younger and outer older leaves of plants treated with supplementary UV‐B or from leaves left to naturally senesce. The amount of hybridized radioactivity was quantified using a phosphorimager; the data shown have been corrected for loading differences by using the counts obtained with 18S rRNA. The data are presented, from the UV‐B experiments, as percentage transcript levels in UV‐B‐treated plants as compared to control plants and from the senescence experiments, as percentage transcript levels in S1 or S2 compared with levels in MG leaves. Values are means±SE of three independent experiments. Conclusion The aim of this study was to investigate whether UV‐B exposure results in cell death through an active process similar to that of developmentally induced senescence, or through a passive process resulting in cellular lysis through necrosis of the tissue. Exposure to supplementary UV‐B radiation resulted in loss of chlorophyll and an increase in lipid damage, as observed during senescence, as well as resulting in the regulation of similar sets of genes in outer older leaves. Exposure to UV‐B resulted in a decrease in the level of a number of PAG genes but more significantly, also led to the induction of a number of SAG genes, including SAG12. The work presented in this paper shows for the first time that, in older outer leaves of Arabidopsis thaliana leaves, exposure to UV‐B results in biochemical and molecular changes that are a consequence of active processes involving regulation of many genes also known to be associated with natural senescence. 3 Present address and to whom correspondence should be sent: Ministry of Agriculture Fisheries and Foods, Room 701, Cromwell House, Dean Stanley Street, London SW1P 3JH, UK. Fax: +44 207 238 1504. E‐mail: soheila.amin‐hanjani@maff.gsi.gov.uk. The research was supported by BBSRC competitive strategic grant at HRI. We are grateful to Novartis Corporation, USA for the PR‐1 cDNA, to Dr Joe Clarke from Professor Xinnian Dong's laboratory for the PDF1.2 cDNA and to Dr Michael Weaver from Dr Richard Amasino's laboratory for the SAG cDNAs. We would also like to thank Steve Robertson for the running and maintenance of the Sanyo cabinets, Mike Smith for preparation of the figures and finally Vicky Buchanan‐Wollaston, Richard Napier, Julia Brüggemann, and Matthew Bell for critical reading of this manuscript and many helpful comments. References A‐H‐Mackerness S. 2000. Plant responses to UV‐B stress: what are the key regulators? Plant Growth Regulation  32, 27–39. CrossRef Search ADS   Google Scholar A‐H‐Mackerness S, Jordan BR. 1999. Changes in gene expression in response to UV‐B induced stress. In: Pessarakli M, ed. Handbook of plant and crop stress . New York: Marcel Dekker, 749–768. Google Scholar A‐H‐Mackerness S, Jordan BR, Thomas B. 1997. UV‐B effects on the expression of genes encoding proteins involved in photosynthesis. In: Lumsden PJ, ed. Plants and UV‐B: responses to environmental change . Cambridge: Cambridge University Press, 113–134. Google Scholar A‐H‐Mackerness S, Surplus SL, Blake P, John CF, Buchanan‐Wollaston V, Jordan BR, Thomas B. 1999. UV‐B induced stress and changes in gene expression in Arabidopsis thalaina: role of signalling pathways controlled by jasmonic acid, ethylene and reactive oxygen species. Plant, Cell and Environment  22, 1413–1424. CrossRef Search ADS   Google Scholar A‐H‐Mackerness S, Surplus SL, Jordan BR, Thomas B. 1998. Effects of supplementary UV‐B radiation on photosynthetic transcripts at different stages of development and light levels in pea: role of ROS and antioxidant enzymes. Photochemistry Photobiology  68, 88–96. CrossRef Search ADS   Google Scholar Arnott T, Murphy TM. 1991. A comparison of the effects of a fungal elicitor and UV radiation on ion transport and hydrogen peroxide synthesis in rose cells. Environmental and Experimental Botany  31, 209–216. CrossRef Search ADS   Google Scholar Bate NJ, Rothstein SJ, Thomson JE. 1991. Expression of nuclear and chloroplast photosynthetic specific genes during leaf senescence. ExJournal of Experimental Botany  42, 801–811. CrossRef Search ADS   Google Scholar Brosche M, Strid Å. 1999. Cloning, expression and molecular characterization of a small pea gene family regulated by low levels of U‐B radiation and other stresses. Plant Physiology  121, 479–487. CrossRef Search ADS PubMed  Google Scholar Buchanan‐Wollaston V. 1997. The molecular biology of leaf senescence. Journal of Experimental Botany  48, 181–199. CrossRef Search ADS   Google Scholar Dai Q, Yan B, Huang S, Liu X, Peng S, Miranda MLM, Chavez AQ, Vegara BS, Olszyk D. 1997. Response of oxidative stress defence systems in rice leaves with supplementary UV‐B radiation. Physiologia Plantarum  101, 301–308. CrossRef Search ADS   Google Scholar Dhindsa RJ, Dhindsa PP. 1981. Leaf senescence correlated with increased levels of membrane permeability and lipid peroxidation and decreased levels of superoxide dismutase and catalase. Journal of Experimental Botany  32, 93–101. CrossRef Search ADS   Google Scholar Gan S, Amasino RM. 1997. Making sense of senescence. Plant Physiology  113, 313–319. CrossRef Search ADS PubMed  Google Scholar Green R, Fluhr R. 1995. UV‐B induced PR‐1 accumulation is mediated by active oxygen species. The Plant Cell  7, 203–212. CrossRef Search ADS PubMed  Google Scholar Grove A, Mohanty P. 1992. Leaf senescence induced alternations in structure and function of higher plant chloroplasts. In: Abrol YP, Mohanty P, Govindjee P, eds. Photosynthesis: photoreactions to plant productivity . The Netherlands: Kluwer Academic Publishers, 225–255. Google Scholar Hensel LL, Grbic V, Baumgarten DA, Bleecker AB. 1993. Developmental and age‐related processes that influence the longevity and senescence of photosynthetic tissues in Arabidopsis. The Plant Cell  5, 553–564. CrossRef Search ADS PubMed  Google Scholar Jordan BR. 1996. The effects of UV‐B radiation on plants: a molecular prospective. In: Callow JA, ed. Advances in botanical research . Academic Press, 97–162. Google Scholar Jordan BR, James PE, A‐H‐Mackerness S. 1998. Factors affecting UV‐B induced changes in Arabidopsis gene expression: the role of development, protective pigments and the chloroplast signal. Plant Cell Physiology  39, 769–778. CrossRef Search ADS PubMed  Google Scholar Lohman KN, Gan S, John MC, Amasino RM. 1994. Molecular analysis of natural senescence in Arabidopsis thaliana. Physiologia Plantarum  92, 322–328. CrossRef Search ADS   Google Scholar Lois R. 1994. Accumulation of UV‐absorbing flavonoids induced by UV‐B radiation in Arabidopsisthaliana. Planta  194, 498–503. CrossRef Search ADS   Google Scholar Lu C, Zhang J. 1998. Changes in PSII function during senescence of wheat leaves. Physiologia Plantarum  104, 239–247. CrossRef Search ADS   Google Scholar Mckenzie R, Connor B, Bodeker G. 1999. Increase summertime radiation in New Zealand in response to ozone loss. Science  285, 1709–1711. CrossRef Search ADS PubMed  Google Scholar Miller JD, Arteca RN, Pell EJ. 1999. Senescence‐associated gene expression during ozone‐induced leaf senescence in Arabidopsis. Plant Physiology  120, 1015–1023. CrossRef Search ADS PubMed  Google Scholar Noh Y‐S, Amasino RM. 1999. Regulation of developmental senescence is conserved between Arabidopsis and Brassica napus. Plant Molecular Biology  41, 195–206. CrossRef Search ADS PubMed  Google Scholar Noodén LD, Guiamet JJ, John I. 1997. Senescence mechanisms. Physiologia Plantarum  101, 746–753. CrossRef Search ADS   Google Scholar Pontier D, Gan S, Amasino RM, Roby D, Lam E. 1999. Markers for hypersensitive response and senescence show distinct patterns of expression. Plant Molecular Biology  39, 1243–1255. CrossRef Search ADS PubMed  Google Scholar Sharma YK, Leon J, Raskin I, Davis KR. 1996. Ozone‐induced responses in Arabidopsis thaliana: the role of salicylic acid in the accumulation of defence‐related transcripts and induced resistance. Proceedings of the National Academy of Sciences USA  93, 5099–5104. CrossRef Search ADS   Google Scholar Smart CM. 1994. Gene expression during leaf senescence. New Phytologist  126, 419–448. CrossRef Search ADS   Google Scholar Strid A, Chow WS, Anderson JM. 1994. UV‐B damage and protection at the molecular level in plants. Photosynthesis Research  39, 475–489. CrossRef Search ADS PubMed  Google Scholar Surplus SL, Jordan BR, Murphy AM, Carr JP, Thomas B, A‐H‐Mackerness S. 1998. UV‐B induced responses in Arabidopsis thaliana: role of salicylic acid and ROS in the regulation of transcripts and acidic PR proteins. Plant, Cell and Environment  21, 685–694. CrossRef Search ADS   Google Scholar Thomas H, Stoddart L. 1980. Leaf senescence. Annual Reviews in Plant Physiology  31, 83–111. CrossRef Search ADS   Google Scholar Thompson JE, Froese CD, Hong Y, Hudak KA, Smith MD. 1997. Membrane deterioration during senescence. Canadian Journal of Botany  75, 867–879. CrossRef Search ADS   Google Scholar Weaver LM, Himelblau E, Amasino RM. 1997. Leaf senescence: gene expression and regulation. In: Setlow JK, ed. Genetic engineering , Vol 19. New York: Plenum Press, 215–234. Google Scholar Zerefos CS, Balis D, Bais AF, Gillotay D, Simon PC, Mayer B, Seckmeyer G. 1997. Variability of UV‐B at four stations in Europe. Geophysical Research Letters  24, 1363–1366. CrossRef Search ADS   Google Scholar © Society for Experimental Biology http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Experimental Botany Oxford University Press

Ultraviolet‐B exposure leads to up‐regulation of senescence‐associated genes in Arabidopsis thaliana

Loading next page...
 
/lp/oxford-university-press/ultraviolet-b-exposure-leads-to-up-regulation-of-senescence-associated-apcqKy1Ufq

References (28)

Publisher
Oxford University Press
Copyright
© Society for Experimental Biology
ISSN
0022-0957
eISSN
1460-2431
DOI
10.1093/jexbot/52.359.1367
Publisher site
See Article on Publisher Site

Abstract

Abstract Exposure to UV‐B radiation resulted in a loss of chlorophyll and an increase in lipid damage in a similar manner to that induced during natural senescence. In addition, exposure to UV‐B led to the induction of a number of genes associated with senescence (SAG12, 13, 14, and 17). These results show, for the first time, that exposure to UV‐B can lead to cellular decline through active and regulated processes involving many genes also associated with natural senescence. Arabidopsis, photosynthetic genes, senescence associated genes, ultraviolet‐B radiation. PAGs, photosynthesis‐associated genes, SAGs, senescence‐associated genes, UV‐B, ultraviolet‐B radiation Introduction Persistent depletion of the stratospheric ozone layer is continuing to result in increases in the levels of ultraviolet‐B radiation (UV‐B: 280–320 nm) reaching the Earth's surface (Mckenzie et al., 1999; Zerefos et al., 1997). UV‐B radiation is biologically very active and exposure to both artificial high (control environment), as well as realistic (field experiments), levels has been shown to lead to changes in plant growth and development as well as result in profound changes in gene expression (for review see Strid et al., 1994; Jordan, 1996). There is, however, considerable developmental variation in sensitivity to UV‐B radiation. In both Arabidopsis and pea, older leaves were found to become damaged by UV‐B faster and to a greater extent than younger leaves or organs (Lois, 1994; A‐H‐Mackerness et al., 1998; Jordan et al., 1998). Exposure was found to lead to an initial phase of chlorophyll loss followed by desiccation of the tissue. At the biochemical level, the rate of photosynthesis is greatly reduced in these leaves, primarily as a result of a decline in RUBISCO protein levels and disruption to the chloroplast membranes. Recent studies have shown that some of these changes can be attributed partially to effects of UV‐B on expression of genes encoding key photosynthetic proteins (Strid et al., 1994; A‐H‐Mackerness and Jordan, 1999). Thus, in leaves at a certain stage of development, exposure can induce changes at the physiological, biochemical and molecular levels that resemble symptoms identified in plants undergoing senescence. Senescence in plants is highly organized and appears to involve not only the breakdown of macromolecules such as proteins and lipids, but also further catabolism/ anabolism of these molecules into forms for transport and retrieval by the rest of the plant (for reviews see Smart, 1994; Noodén et al., 1997). A decline in photosynthesis and a loss of chlorophyll are early symptoms of senescence, with chloroplasts one of the primary targets for degradation (Thomas and Stoddart, 1980; Grove and Mohanty, 1992). Although the actual processes involved in senescence of photosynthetic tissue have been characterized in a number of plant species, the regulatory mechanisms that govern the timing of leaf senescence remains elusive. However, senescence is thought to be under genetic control and recent studies have shown that differential expression of specific genes is associated with the senescence syndrome (for reviews see Buchanan‐Wollaston, 1997; Weaver et al., 1997). During leaf senescence transcripts for key photosynthetic proteins decline (Bate et al., 1991; Hensel et al., 1993). In addition, expression of a variety of genes is induced, including those represented by the SAG clones identified from naturally senescing Arabidopsis leaves (Lohman et al., 1994). A number of these senescence‐associated genes have been cloned and sequenced. Among these identified clones are genes encoding proteases (SAG12), glutamine synthase (Atgsr2), ACC synthase (ACS6), lipases, glyoxylate cycle enzymes, and polyubiquitin which may be involved in protein degradation and nitrogen remobilization. Others, which encode for metal‐binding proteins (SAG14), metallothionein (SAG17), catalase (LSC650), and cytochrome P450, likely function to scavenge and detoxify reactive oxygen species (Buchanan‐Wollaston, 1997; Weaver et al., 1997). There are also a number of isolated SAG cDNA clones that have no obvious senescence‐related function and many others still remain unidentified. Leaf senescence progresses in an age‐dependent manner, but both endogenous and exogenous factors can greatly influence the timing of this process. Thus, phytohormones, shading, temperature, and oxidative stresses, such as pathogen infection and ozone treatment, can all lead to premature senescence of the tissue (Smart, 1994; Gan and Amasino, 1997). UV‐B exposure has been shown to lead to the generation of reactive oxygen species (ROS) (Arnott and Murphy, 1991; Green and Fluhr, 1995; Dai et al., 1997) and a number of studies have highlighted the similarities between responses to UV‐B and other oxidative stresses including pathogen infection and ozone treatment (see A‐H‐Mackerness, 2000, and references within). However, despite the extensive work carried out in the last two decades, relatively little is known about the mechanisms by which higher plants perceive UV‐B radiation and the processes that are involved in initiating the physiological responses to this stress. Therefore, in order to determine the nature of cell death induced by UV‐B, a number of physiological, biochemical and molecular processes involved in UV‐B induced responses in older leaves of Arabidopsis and those brought about through natural senescence have been characterized and compared in this study. Materials and methods Plant material, experimental conditions and feeding experiments Arabidopsis thaliana (Columbia (MGH)) was used in all experiments. Seeds were treated for 3 d at 4 °C after sowing on a compost:sand:vermiculite mixture and then transferred to a Sanyo phytotron with 12 h light (22 °C), 12 h dark (16 °C) cycles at 70% humidity. At 14 d the seedlings were transplanted into individual pots and grown for a further 14 d. Incident irradiation was provided by Philips warm white fluorescent tubes giving a fluence rate of 150 μmol m−2 s−1 photosynthetically active radiation (400–700 nm). Half the plants were then given supplementary UV‐B radiation from four UV lamps (Philips TL 12, 40 W) during the photoperiod. The fluence rate between 280 and 320 was 3.2 μmol m−2 s−1. The UV lamps were covered with cellulose acetate sheets, which were changed daily, to exclude UV radiation below 290 nm. The plants in the other cabinet (controls) were subjected to the same treatment, but the UV lamps were covered with Mylar film to exclude radiation below 320 nm. Each experiment was repeated at least three times with similar results. For the UV‐B experiments, the outer older rosette leaves or the inner three whorls of the younger leaves were taken at random from plants in different parts of the cabinets, 6 h into each photoperiod (unless otherwise stated) and at least three plants were used per sample for analysis. For the naturally senescent leaves, the lower rosette leaves were taken from at least five plants grown for 4 weeks (MG, mature green), 5 weeks (S1, early senescence) and 8 weeks (S2, mid‐senescence showing signs of yellowing) in the absence of UV‐B or UV‐A. Purification of total RNA, northern blotting and hybridization Total RNA was extracted from Arabidopsis leaves (0.5 g) as described previously (Jordan et al., 1998). RNA analysis, blotting, prehybridization, hybridization, washes, and autoradiography were as described earlier (A‐H‐Mackerness et al., 1999). The Lhcb, psbA, PR‐1, and PDF1.2 cDNA probes were described earlier (A‐H‐Mackerness et al., 1999). The cDNA for the SAG genes SAG12, 13, 14 and 17 are described previously (Lohman et al., 1994). The blots presented are representative of three or more independent experiments. Relative amounts of radioactivity bound to specific bands were quantified using a Phosphorimager SI (Molecular Dynamics Ltd, Bucks, UK). Loading control analysis of each blot was carried out by hybridization using an 18S rRNA probe from pea (see Surplus et al., 1998, for details). The data are presented, from the UV‐B experiments, as percentage transcript levels in UV‐B‐treated plants as compared to plants treated under control conditions and from the senescence experiments, as percentage transcript levels in S1 or S2 leaves compared with levels in MG leaves. Lipid peroxide (malondialdehyde) and chlorophyll quantification The lipid peroxidation (MDA) assays were carried out as described earlier (A‐H‐Mackerness et al., 1998). Chlorophyll (Chl) analysis was carried out with approximately 0.5 g of leaf tissue and using the method described earlier (Jordan et al., 1998). Measurement of PS II Chl fluorescence (Fv/Fm) Chl fluorescence was determined by using a Hansatech plant efficiency analyser (Hansatech, Kings Lynn, UK). The leaves were dark adapted for 5 min prior to measurement for 30 s as previously described (Jordan et al., 1998). Statistical analysis A factorial analysis of variance (ANOVA) was performed for the chlorophyll, MDA and Fv/Fm values. Standard errors of the differences of the means (SED) were determined from the ANOVA. Results and discussion The effects of UV‐B radiation on plants have been extensively studied in a large number of plant species (A‐H‐Mackerness and Jordan, 1999). However, because UV‐B is high‐energy radiation and absorbed by all macromolecules, it is still unclear which responses to UV‐B are specific and mediated through receptors and which are due to non‐specific damage. The response to UV‐B depends heavily on a number of parameters including the developmental stage of tissue studied (for further discussion see A‐H‐Mackerness and Jordan, 1999). Although a small number of studies have tried to address the mechanism behind developmental variation in sensitivity to UV‐B, little has been done to determine the process by which older leaves deteriorate due to exposure to UV‐B. Consequently, the effects of UV‐B on a number of biochemical and molecular markers of senescence were determined in the lower rosette leaves of Arabidopsis plants. These leaves were showing signs of chlorosis by the third day of UV‐B treatment (data not shown). The older, outer leaves treated with supplementary UV‐B showed signs of premature senescence, with a loss of chlorophyll and increases in membrane degradation in a manner similar to the effects detected in naturally senescent leaves (Fig. 1a, b). In contrast, no significant change in either parameter was observed in plants treated under control conditions. Previous studies have indicated that chlorophyll loss does occur in the outer leaves, but not the younger inner leaves, of Arabidopsis plants exposed to supplementary UV‐B (Jordan et al., 1998) and similar declines have been reported for senescent leaves (Hensel et al., 1993; Lohman et al., 1994). Degradation of membranes and a decline in the level of lipids in senescent tissue has been reported (Thompson et al., 1997) and increases in levels of MDA, indicating lipid peroxidation, have been found during senescence (Dhindsa and Dhindsa, 1981). Similarly, a rise in MDA levels has been shown to occur in response to UV‐B exposure in a number of plant species (Arnott and Murphy, 1991; Dai et al., 1997; A‐H‐Mackerness et al., 1998). In contrast to similar patterns of change in lipid and chlorophyll levels in both leaves treated with UV‐B and undergoing natural senescence, the maximum quantum efficiency of PSII photochemisty (Fv/Fm) was not affected in naturally senescent leaves, while levels significantly fell in leaves treated with UV‐B (Fig. 1c). These observations are in accordance with recent studies carried out on whole plants. Fv/Fm has been shown to be only slightly affected as leaves senesce even though a substantial decrease in the chlorophyll content occurs (Lu and Zhang, 1998). In contrast, PSII has been identified as one of the most UV‐B labile components of the photosynthetic system and thus dramatic losses of PSII efficiency have been reported in a variety of plant species exposed to supplementary UV‐B radiation (see Jordan, 1996, and references within). Profound changes in gene expression have been reported in leaves undergoing natural senescence (Buchanan‐Wollaston, 1997; Weaver et al., 1997) as well as in leaves treated with supplementary UV‐B (Strid et al., 1994; A‐H‐Mackerness, 2000). Thus the possibility that the same genes are regulated in the two sets of responses was investigated. In the outer older leaves UV‐B exposure resulted in a decline in both photosynthetic associated genes (PAGs), Lhcb and psbA, after 1 d with levels continuing to fall during subsequent days. A similar decline in transcripts was also detected in leaves undergoing senescence (Fig. 2a). Decline in these transcripts has been reported previously in naturally senescent leaves (Lohman et al., 1994) and within the same time scale of this study in the older outer, but not younger inner, leaves treated with UV‐B (Jordan et al., 1998). Falls in RbcS and rbcL transcripts, and the subsequent decline in RUBISCO level and activity, in UV‐B treated (A‐H‐Mackerness et al., 1997) and senescent tissues (Bate et al., 1991; Hensel et al. 1993) have also been reported. Transcripts for two pathogen‐related proteins, PR‐1 and PDF1.2, increased in response to UV‐B exposure and during senescence (Fig. 2b). Transcripts of PR‐1 have been shown previously to rise in response to pathogen infection, ozone and UV‐B treatment as well as during senescence (Green and Fluhr, 1995; Buchanan‐Wollaston, 1997; Sharma et al., 1996; Surplus et al., 1998). A number of senescence‐associated genes (SAGs) have been catalogued from naturally senescing Arabidopsis leaves (Lohman et al., 1994). Unlike the effect of UV‐B on PAGs and PR protein expression, no work has been carried out to determine the effect of UV‐B on these molecular markers of senescence. The level of SAG13, which encodes a short chain alcohol dehydrogenase, and SAG14, which encodes a blue copper‐binding protein, both increased in the outer leaves on exposure to UV‐B after just 1 d of UV‐B treatment and continued to increase (Fig. 2c). Similarly, Brosche and Strid have shown that transcripts encoding for another alcohol dehydrogenase increases on exposure to UV‐B radiation (Brosche and Strid, 1999), but as in senescence, the exact function of this enzyme in tolerance/defence against UV‐B is unclear. Levels of both SAG13 and 14 were also induced by ozone treatment (Miller et al., 1999) and thus it is possible that these proteins play a role in oxidative stress responses rather than having a specific or unique role during senescence. The slow induction of these transcripts in inner, young leaves, and the high levels in outer leaves as compared to senescing leaves also further indicates a function more related to stress than directly in senescence (Fig. 2). Expression of the metallothionein gene, SAG17, was also induced in outer and, to a much lesser extent, in inner leaves by exposure to supplementary UV‐B (Figs 2c, 3). Interestingly, SAG17 was not induced by exposure to the oxidative stress ozone (Miller et al., 1999), although increases in naturally senescing tissue have been reported extensively (Lohman et al., 1994; Weaver et al., 1997). Similarly, transcripts encoding SAG12, which encodes a cysteine protease, rose during senescence (Fig. 2c; Lohman et al., 1994; Noh and Amasino, 1999) and only in outer leaves after 3 d of UV‐B exposure (Fig. 2c), but not in inner leaves (Fig. 2), after ozone treatment (Miller et al., 1999) or pathogen infection (Pontier et al., 1999). Unlike the expression levels of the other SAGs which were either lower or comparable in senescent and outer leaves treated with UV‐B, the transcript levels of SAG12 were significantly higher in S2 leaves than in the UV‐B treated leaves. SAG12 is one of the few genes identified to date where expression is closely linked to senescence and is not increased by many other stress treatments (Gan and Amasino, 1997; Weaver et al., 1997; Noh and Amasino, 1999). Thus the difference in SAG12 levels in the outer UV‐B‐treated leaves and the S2 leaves is likely due to comparison of tissue at different ‘stages’ of senescence. Fig. 1. View largeDownload slide Quantitative changes in (a) chlorophyll, (b) lipid peroxide (MDA) and (c) chl fluorescence (Fv/Fm) in UV‐B treated outer older and naturally senescent leaves of Arabidopsis thaliana. Measurements were taken from the outer leaves of 4‐week‐old plants which were treated with or without UV‐B for 1, 2 and 3 d or from leaves of plants left to senesce naturally (MG, mature green; S1, early senescence; S2, mid‐senescence showing signs of yellowing). For the UV‐B experiments, the outer rosette leaves were taken at random from plants in different parts of the cabinets, 6 h into each photoperiod and at least three plants were used per sample for analysis. For the senescence experiments, the lower rosette leaves were taken from at least five plants grown for 4 weeks (MG), 5 weeks (S1) and 8 weeks (S2) in the absence of UV‐B or UV‐A. Each point is an average of three independent experiments and the error bars indicate the standard error of the differences of the means (SED). Fig. 1. View largeDownload slide Quantitative changes in (a) chlorophyll, (b) lipid peroxide (MDA) and (c) chl fluorescence (Fv/Fm) in UV‐B treated outer older and naturally senescent leaves of Arabidopsis thaliana. Measurements were taken from the outer leaves of 4‐week‐old plants which were treated with or without UV‐B for 1, 2 and 3 d or from leaves of plants left to senesce naturally (MG, mature green; S1, early senescence; S2, mid‐senescence showing signs of yellowing). For the UV‐B experiments, the outer rosette leaves were taken at random from plants in different parts of the cabinets, 6 h into each photoperiod and at least three plants were used per sample for analysis. For the senescence experiments, the lower rosette leaves were taken from at least five plants grown for 4 weeks (MG), 5 weeks (S1) and 8 weeks (S2) in the absence of UV‐B or UV‐A. Each point is an average of three independent experiments and the error bars indicate the standard error of the differences of the means (SED). Fig. 2. View largeDownload slide Transcripts levels in wild‐type Arabidopsis plants exposed to supplementary UV‐B or left to senesce naturally (for details see Materials and methods). (i) Northern blot analysis showing transcripts of (a) photosynthetic genes, (b) defence‐associated genes and (c) senescence‐associated genes in UV‐B‐treated and naturally senescing leaves. RNA was extracted from the outer leaves of 4‐week‐old plants which were treated with (UV) or without (C) supplementary UV‐B radiation for 1, 2 and 3 d or from leaves of plants left to senesce naturally (for further details see Fig. 1 legend). The blots shown are representative of results obtained from three separate independent experiments. Fig. 2. View largeDownload slide Transcripts levels in wild‐type Arabidopsis plants exposed to supplementary UV‐B or left to senesce naturally (for details see Materials and methods). (i) Northern blot analysis showing transcripts of (a) photosynthetic genes, (b) defence‐associated genes and (c) senescence‐associated genes in UV‐B‐treated and naturally senescing leaves. RNA was extracted from the outer leaves of 4‐week‐old plants which were treated with (UV) or without (C) supplementary UV‐B radiation for 1, 2 and 3 d or from leaves of plants left to senesce naturally (for further details see Fig. 1 legend). The blots shown are representative of results obtained from three separate independent experiments. Fig. 3. View largeDownload slide Quantitative changes in SAG12, 13, 14, and 17 transcript levels from inner younger and outer older leaves of plants treated with supplementary UV‐B or from leaves left to naturally senesce. The amount of hybridized radioactivity was quantified using a phosphorimager; the data shown have been corrected for loading differences by using the counts obtained with 18S rRNA. The data are presented, from the UV‐B experiments, as percentage transcript levels in UV‐B‐treated plants as compared to control plants and from the senescence experiments, as percentage transcript levels in S1 or S2 compared with levels in MG leaves. Values are means±SE of three independent experiments. Fig. 3. View largeDownload slide Quantitative changes in SAG12, 13, 14, and 17 transcript levels from inner younger and outer older leaves of plants treated with supplementary UV‐B or from leaves left to naturally senesce. The amount of hybridized radioactivity was quantified using a phosphorimager; the data shown have been corrected for loading differences by using the counts obtained with 18S rRNA. The data are presented, from the UV‐B experiments, as percentage transcript levels in UV‐B‐treated plants as compared to control plants and from the senescence experiments, as percentage transcript levels in S1 or S2 compared with levels in MG leaves. Values are means±SE of three independent experiments. Conclusion The aim of this study was to investigate whether UV‐B exposure results in cell death through an active process similar to that of developmentally induced senescence, or through a passive process resulting in cellular lysis through necrosis of the tissue. Exposure to supplementary UV‐B radiation resulted in loss of chlorophyll and an increase in lipid damage, as observed during senescence, as well as resulting in the regulation of similar sets of genes in outer older leaves. Exposure to UV‐B resulted in a decrease in the level of a number of PAG genes but more significantly, also led to the induction of a number of SAG genes, including SAG12. The work presented in this paper shows for the first time that, in older outer leaves of Arabidopsis thaliana leaves, exposure to UV‐B results in biochemical and molecular changes that are a consequence of active processes involving regulation of many genes also known to be associated with natural senescence. 3 Present address and to whom correspondence should be sent: Ministry of Agriculture Fisheries and Foods, Room 701, Cromwell House, Dean Stanley Street, London SW1P 3JH, UK. Fax: +44 207 238 1504. E‐mail: soheila.amin‐hanjani@maff.gsi.gov.uk. The research was supported by BBSRC competitive strategic grant at HRI. We are grateful to Novartis Corporation, USA for the PR‐1 cDNA, to Dr Joe Clarke from Professor Xinnian Dong's laboratory for the PDF1.2 cDNA and to Dr Michael Weaver from Dr Richard Amasino's laboratory for the SAG cDNAs. We would also like to thank Steve Robertson for the running and maintenance of the Sanyo cabinets, Mike Smith for preparation of the figures and finally Vicky Buchanan‐Wollaston, Richard Napier, Julia Brüggemann, and Matthew Bell for critical reading of this manuscript and many helpful comments. References A‐H‐Mackerness S. 2000. Plant responses to UV‐B stress: what are the key regulators? Plant Growth Regulation  32, 27–39. CrossRef Search ADS   Google Scholar A‐H‐Mackerness S, Jordan BR. 1999. Changes in gene expression in response to UV‐B induced stress. In: Pessarakli M, ed. Handbook of plant and crop stress . New York: Marcel Dekker, 749–768. Google Scholar A‐H‐Mackerness S, Jordan BR, Thomas B. 1997. UV‐B effects on the expression of genes encoding proteins involved in photosynthesis. In: Lumsden PJ, ed. Plants and UV‐B: responses to environmental change . Cambridge: Cambridge University Press, 113–134. Google Scholar A‐H‐Mackerness S, Surplus SL, Blake P, John CF, Buchanan‐Wollaston V, Jordan BR, Thomas B. 1999. UV‐B induced stress and changes in gene expression in Arabidopsis thalaina: role of signalling pathways controlled by jasmonic acid, ethylene and reactive oxygen species. Plant, Cell and Environment  22, 1413–1424. CrossRef Search ADS   Google Scholar A‐H‐Mackerness S, Surplus SL, Jordan BR, Thomas B. 1998. Effects of supplementary UV‐B radiation on photosynthetic transcripts at different stages of development and light levels in pea: role of ROS and antioxidant enzymes. Photochemistry Photobiology  68, 88–96. CrossRef Search ADS   Google Scholar Arnott T, Murphy TM. 1991. A comparison of the effects of a fungal elicitor and UV radiation on ion transport and hydrogen peroxide synthesis in rose cells. Environmental and Experimental Botany  31, 209–216. CrossRef Search ADS   Google Scholar Bate NJ, Rothstein SJ, Thomson JE. 1991. Expression of nuclear and chloroplast photosynthetic specific genes during leaf senescence. ExJournal of Experimental Botany  42, 801–811. CrossRef Search ADS   Google Scholar Brosche M, Strid Å. 1999. Cloning, expression and molecular characterization of a small pea gene family regulated by low levels of U‐B radiation and other stresses. Plant Physiology  121, 479–487. CrossRef Search ADS PubMed  Google Scholar Buchanan‐Wollaston V. 1997. The molecular biology of leaf senescence. Journal of Experimental Botany  48, 181–199. CrossRef Search ADS   Google Scholar Dai Q, Yan B, Huang S, Liu X, Peng S, Miranda MLM, Chavez AQ, Vegara BS, Olszyk D. 1997. Response of oxidative stress defence systems in rice leaves with supplementary UV‐B radiation. Physiologia Plantarum  101, 301–308. CrossRef Search ADS   Google Scholar Dhindsa RJ, Dhindsa PP. 1981. Leaf senescence correlated with increased levels of membrane permeability and lipid peroxidation and decreased levels of superoxide dismutase and catalase. Journal of Experimental Botany  32, 93–101. CrossRef Search ADS   Google Scholar Gan S, Amasino RM. 1997. Making sense of senescence. Plant Physiology  113, 313–319. CrossRef Search ADS PubMed  Google Scholar Green R, Fluhr R. 1995. UV‐B induced PR‐1 accumulation is mediated by active oxygen species. The Plant Cell  7, 203–212. CrossRef Search ADS PubMed  Google Scholar Grove A, Mohanty P. 1992. Leaf senescence induced alternations in structure and function of higher plant chloroplasts. In: Abrol YP, Mohanty P, Govindjee P, eds. Photosynthesis: photoreactions to plant productivity . The Netherlands: Kluwer Academic Publishers, 225–255. Google Scholar Hensel LL, Grbic V, Baumgarten DA, Bleecker AB. 1993. Developmental and age‐related processes that influence the longevity and senescence of photosynthetic tissues in Arabidopsis. The Plant Cell  5, 553–564. CrossRef Search ADS PubMed  Google Scholar Jordan BR. 1996. The effects of UV‐B radiation on plants: a molecular prospective. In: Callow JA, ed. Advances in botanical research . Academic Press, 97–162. Google Scholar Jordan BR, James PE, A‐H‐Mackerness S. 1998. Factors affecting UV‐B induced changes in Arabidopsis gene expression: the role of development, protective pigments and the chloroplast signal. Plant Cell Physiology  39, 769–778. CrossRef Search ADS PubMed  Google Scholar Lohman KN, Gan S, John MC, Amasino RM. 1994. Molecular analysis of natural senescence in Arabidopsis thaliana. Physiologia Plantarum  92, 322–328. CrossRef Search ADS   Google Scholar Lois R. 1994. Accumulation of UV‐absorbing flavonoids induced by UV‐B radiation in Arabidopsisthaliana. Planta  194, 498–503. CrossRef Search ADS   Google Scholar Lu C, Zhang J. 1998. Changes in PSII function during senescence of wheat leaves. Physiologia Plantarum  104, 239–247. CrossRef Search ADS   Google Scholar Mckenzie R, Connor B, Bodeker G. 1999. Increase summertime radiation in New Zealand in response to ozone loss. Science  285, 1709–1711. CrossRef Search ADS PubMed  Google Scholar Miller JD, Arteca RN, Pell EJ. 1999. Senescence‐associated gene expression during ozone‐induced leaf senescence in Arabidopsis. Plant Physiology  120, 1015–1023. CrossRef Search ADS PubMed  Google Scholar Noh Y‐S, Amasino RM. 1999. Regulation of developmental senescence is conserved between Arabidopsis and Brassica napus. Plant Molecular Biology  41, 195–206. CrossRef Search ADS PubMed  Google Scholar Noodén LD, Guiamet JJ, John I. 1997. Senescence mechanisms. Physiologia Plantarum  101, 746–753. CrossRef Search ADS   Google Scholar Pontier D, Gan S, Amasino RM, Roby D, Lam E. 1999. Markers for hypersensitive response and senescence show distinct patterns of expression. Plant Molecular Biology  39, 1243–1255. CrossRef Search ADS PubMed  Google Scholar Sharma YK, Leon J, Raskin I, Davis KR. 1996. Ozone‐induced responses in Arabidopsis thaliana: the role of salicylic acid in the accumulation of defence‐related transcripts and induced resistance. Proceedings of the National Academy of Sciences USA  93, 5099–5104. CrossRef Search ADS   Google Scholar Smart CM. 1994. Gene expression during leaf senescence. New Phytologist  126, 419–448. CrossRef Search ADS   Google Scholar Strid A, Chow WS, Anderson JM. 1994. UV‐B damage and protection at the molecular level in plants. Photosynthesis Research  39, 475–489. CrossRef Search ADS PubMed  Google Scholar Surplus SL, Jordan BR, Murphy AM, Carr JP, Thomas B, A‐H‐Mackerness S. 1998. UV‐B induced responses in Arabidopsis thaliana: role of salicylic acid and ROS in the regulation of transcripts and acidic PR proteins. Plant, Cell and Environment  21, 685–694. CrossRef Search ADS   Google Scholar Thomas H, Stoddart L. 1980. Leaf senescence. Annual Reviews in Plant Physiology  31, 83–111. CrossRef Search ADS   Google Scholar Thompson JE, Froese CD, Hong Y, Hudak KA, Smith MD. 1997. Membrane deterioration during senescence. Canadian Journal of Botany  75, 867–879. CrossRef Search ADS   Google Scholar Weaver LM, Himelblau E, Amasino RM. 1997. Leaf senescence: gene expression and regulation. In: Setlow JK, ed. Genetic engineering , Vol 19. New York: Plenum Press, 215–234. Google Scholar Zerefos CS, Balis D, Bais AF, Gillotay D, Simon PC, Mayer B, Seckmeyer G. 1997. Variability of UV‐B at four stations in Europe. Geophysical Research Letters  24, 1363–1366. CrossRef Search ADS   Google Scholar © Society for Experimental Biology

Journal

Journal of Experimental BotanyOxford University Press

Published: Jun 1, 2001

There are no references for this article.