Journal of Experimental Botany

KOHL, DANIEL, H.;KENNELLY, EDWARD, J.;ZHU,, YUXIAN;SCHUBERT, KAREL, R.;SHEARER,, GEORGIA

doi: 10.1093/jxb/42.7.831pmid: N/A

Abstract We examined the effect of drought stress on proline accumulation, nitrogenase activity and activities of enzymes related to proline metabolism in soybean (Glycine max [L.] Merr.) nodules. Nitrogenase (C2H2 reducing) activity was inhibited 90% or more as a result of drought stress. This inhibition was substantially reversed after a 4 h recovery period. Pyrroline-5-carboxylate reductase activity in extracts of drought-stressed nodules from 25-d-old plants was 55% higher than in unstressed nodules, but the same activity in preparations from 55-d-old plants was similar to that of control plants. Extracts of recovering nodules on plants of both ages had activities near those of controls. Drought stress increased the activity of the pentose phosphate pathway by about 65% in extracts of nodules from 55-d-old plants, but there was no effect in extracts of nodules from younger plants (25-d-old). Proline dehydrogenase activity was 3.7 and 1.6 times higher in bacteroids isolated from nodules taken from 25- and 55-d-old stressed plants, respectively, than in comparable control bacteroids. This activity remained high in bacteroids from both sets of recovering nodules. The amount of proline in extracts from stressed nodules was 3- to 4-fold higher than in unstressed nodules, despite increased proline dehydrogenase activity and remained high in nodules collected 4 h after rewatering. This increase was observed in both cytoplasmic and bacteroid fractions. The possible physiological significance of these results is discussed. Proline metabolism, pentose phosphate pathway, drought stress, soybean nodules This content is only available as a PDF. Author notes 1This was supported by Public Health Service rant GM38786 from the National Institutes of Health © Oxford University Press

HUNGRIA,, M.;BARRADAS, C. A., A.;WALLSGROVE, R., M.

doi: 10.1093/jxb/42.7.839pmid: N/A

Abstract In nodulated common bean (Phaseolus vulgaris L.), there is typically a period of N stress between 15 and 20 d after emergence (DAE), due to a lack of synchronization between the depletion of N in the cotyledons and the beginning of N2 fixation and transport. Screening trials identified some Rhizobium leguminosarum bv. phaseoli strains with which symptoms of N deficiency were not visible (‘precocious’ strains). Cultivar Negro Argel was then inoculated with two ‘traditional’ strains (C-05 and CIAT 727) and two ‘precocious’ strains (CNPAF 146 and CNPAF 512), and plants were harvested from 8 to 30 DAE. There were no differences between the two groups of strains in nodule dry weight or in the acetylene reduction rates between 8 and 16 DAE. However, nodules induced by the ‘precocious’ strains showed earlier onset of glutamine synthetase (GS) (EC 6.3.1.2) and glutamate synthase (GOGAT) (EC 1.4.1.14) activities, and ureide synthesis. The N concentration in the nodules formed by ‘precocious’ strains varied from 4.2 to 4.5%, whereas with the ‘traditional’ strains, it increased from 3.2% at 8 DAE to 65% at 18 DAE, at which time plants exhibited N-deficiency symptoms. By 21 DAE, GS and GOGAT activities in ‘traditional’ nodules were increased, as well as the ureide-N-concentration in the xylem sap, nodule N content declined to 4.5% and the leaves became green. These results suggest that the N stress with ‘traditional’ strains is not a limitation in early N2 fixation activity but rather in the rates of expression of the processes of N assimilation and transport. Glutamate synthase, glutamine synthetase, nitrogen fixation, Phaseolus vulgaris, Rhizobium This content is only available as a PDF. © Oxford University Press

PAUL, MATTHEW, J.;DRISCOLL, SIMON, P.;LAWLOR, DAVID, W.

doi: 10.1093/jxb/42.7.845pmid: N/A

Abstract Sunflower plants (Helianthus annuus L.) grown at 30°C were cooled to 13°C in the light in atmospheric CO2 or low CO2, or in darkness. Photosynthetic rate at 30°C after cooling whole plants in atmospheric CO2 for 12 h during a photoperiod was significantly lower than at the start of the photoperiod compared to plants cooled at low CO2, those cooled in the dark and those maintained at 30°C. Amounts of sucrose, hexoses and starch in leaves at 13°C increased throughout a 14 h photoperiod to levels higher than in leaves at 30°C, where amounts of sucrose and hexoses were stable or falling after 4 h. Carbohydrate accumulation at 13°C during this photoperiod was more than twice that at 30°C. After three photoperiods and two dark periods at 13°C carbohydrate levels in leaves were still as high as at the end of the first photoperiod, but less carbohydrate accumulated during the photoperiods than during the first photoperiod, and more was partitioned as starch. Amounts of soluble carbohydrate in roots were greater after 14 h at 13°C than in roots of plants at 30°C. Loss of 14C from leaves at 30°C as a proportion of 14CO2 fixed by them at 30°C, decreased after exposure of plants to 13°C in the light for 30 min prior to 14CO2feeding. Results indicate an effect of cold on the transport process that was light-dependent. It is inferred that the reduction in the proportion of 14C lost from leaves after 10 h cooling was due to reduced sink demand, whereas the rise in the proportion of 14C lost from leaves after 24 h reflects reduced photosynthetic rate. The coincidence of reduced photosynthetic rate with raised carbohydrate levels in leaves maintained at 30°C throughout, whilst the rest of the plant was cooled to 13°C in the light implies feedback inhibition of photosynthesis. This may reduce the imbalance between source and sink in sunflower during the first days of long-term cooling. Temperature, carbon export, carbohydrates, photosynthesis, sunflower This content is only available as a PDF. Author notes 1Present address: Lehrstuhl fur Pflanzenphysiologie, Universitat Bayreuth, Bayreuth D-8580, Germany © Oxford University Press

BUNCE, JAMES, A.

doi: 10.1093/jxb/42.7.853pmid: N/A

Abstract Photosynthetic acclimation was examined by exposing third trifoliolate leaves of soybeans to air temperatures of 20 to 30°C and photosynthetic photon flux densities (PPFD) of 150 to 950μmol photons m−2 s−1 for the last 3 d before they reached maximum area. In some cases the environment of the third leaf was controlled separately from that of the rest of the plant. Photosynthesis, respiration and dry mass accumulation were determined under the treatment conditions, and photosynthetic capacity, and dry mass and protein content were determined at full expansion. Photosynthetic capacity, the light-saturated rate of net carbon dioxide exchange at 25°C and 34 Pa external partial pressure of carbon dioxide, could be modified between 21 and 35 μmol CO2 m−2 s−1 by environmental changes after leaves had become exporters of photosynthate. Protein per unit leaf mass did not differ between treatments, and photosynthetic capacity increased with leaf mass per unit area. Photosynthetic capacity of third leaves was affected by the PPFD incident on those leaves, but not by the PPFD on other leaves on the plant. Photosynthetic capacity of third leaves was affected by the temperature of the rest of the plant, but not by the temperature of the third leaves. Photosynthetic capacity was linearly related to carbon dioxide exchange rate in the growth regimes, but not to daytime PPFD. At high PPFD, and at 25 and 30°C, mass accumulation was about 28% of the mass of photosynthate produced. At lower PPFD, and at 20°C, larger percentages of the photosynthate produced accumulated as dry mass. The results suggest that photosynthate supply is an important factor controlling leaf structural growth and, consequently, photosynthetic acclimation to light and temperature. Glycine max (L.) Merr., photosynthesis, temperature acclimation, light acclimation, photosynthate partitioning This content is only available as a PDF. © Oxford University Press

BASU, P., S.;MINHAS, J., S.

doi: 10.1093/jxb/42.7.861pmid: N/A

Abstract Six potato genotypes with different degrees of heat tolerance were grown in pots at 38/25 'b0C maximum/minimum temperature at 14 h daylength under natural light glasshouse conditions. Prior to sampling, the plants were given a 14 h dark period. Photosynthesis was measured at 28 'b0C and at a saturating light intensity of more than 1200 μEm-2 s-1. During the optimum photosynthetic period (09.00–12.30 h), the leaves of heat-tolerant potato genotypes (DTO-28, Norchip, and Desiree) had 4–5 times more soluble sugars (mainly sucrose) and higher sucrose-phosphate synthase activity than the leaves of the heat-susceptible genotypes (Kufri Jyoti, Kufri Chandramukhi, and Kufri Muthu). However, starch accumulation in leaves of susceptible genotypes was about twice that in tolerant genotypes. All susceptible genotypes showed a low rate of assimilate transport from leaves and a higher shoot/root ratio which indicated that the shoot remained the predominant sink for photosynthate. Activities of amylase and invertase in leaves were also higher in susceptible genotypes. It is suggested that the poor yield of heat-susceptible genotypes at high temperature and long day conditions is related to insufficient availability of the transportable sugar, sucrose. Solarium tuberosum, carbon partitioning, heat stress This content is only available as a PDF. Author notes 1Publication No. 1210, CPRI, Shimla. © Oxford University Press

DYE, P., J.;OLBRICH, B., W.;POULTER, A., G.

doi: 10.1093/jxb/42.7.867pmid: N/A

Abstract Heat pulse velocity (HPV) apparatus was used to investigate the relation between the radial HPV profile and the position of growth rings in two Pinus patula trees (aged 4 and 7 years), growing in Frankfort State Forest in the eastern Transvaal, South Africa. Successive measurements of HPV at 3.0 mm intervals along each of four radii in each tree revealed a cyclical pattern, with maxima and minima correlated with summer and winter wood, respectively. We recommend that probe emplacement in fast-growing pines with relatively wide growth rings should be to randomly-assigned depths in the sapwood. Confidence limits associated with sample means of wound-corrected HPV obtained with 4, 8 or 12 probe sets were generated by simulating the repeated selection of a randomly-chosen HPV measurement from each sapwood radius. We conclude from this analysis that a minimum of 12 point measurements per tree is required to obtain an acceptable estimate of sap flow. In older trees where a decline in HPV is expected towards the centre of the trunk, sampling must be modified to avoid bias caused by deeper measurements representing proportionately less of the total sapwood area than those taken at more shallow depths in the sapwood. Pinus patula, heat pulse velocity, sap flow, growth rings This content is only available as a PDF. © Oxford University Press

MOHAPATRA, P., K.;SAHU, S., K.

doi: 10.1093/jxb/42.7.871pmid: N/A

Abstract Two high yielding semi-dwarf rice varieties namely IR-36 and Java, and one traditional tall indica rice variety, Akul, were cultivated in the dry and wet seasons, respectively, in 1987 under irrigated field conditions. A few days after visible panicle initiation, the panicle on the main shoot was dissected out to measure development, growth, soluble carbohydrates, amino acid and phosphate contents of individual primary branches. Primary branch developmnent was quantified by noting the average time to anthesis of spikelets on the branch. The pattern of development was hierarchical with each successive branch dominating the one immediately below it and hence, the measure of development increased in an acropetal fashion from the bottom to the top in all varieties. However, in comparison to the developmentally advanced distal branches, the branches at the proximal region had the potential to generate larger numbers of spikelets, although actual potential to produce grains in them was quite poor. Almost 2 weeks prior to mean anthesis, the gradient in assimilate concentration of the primary branches was found to increase acropetally from bottom to top and correlated negatively with the developmental score (high score indicates less development and vice versa). During the following week, the situation reversed and a higher concentration of assimilates was found in the lower branches than in the upper. Subsequent observations taken before mean anthesis showed assimilate contents to be correlated positively with the developmental score. The role of assimilates in spikelet development on the primary branches has been discussed and it is concluded that there is no clear causative relationship between assimilate concentration and spikelet development. In the post anthesis period, little difference in assimilate concentration of the branches was observed. The presence of a higher concentration of assimilates did not help spikelet survival on the proximal branches any more than that on the distal. Rice, spikelet, primary branch, anthesis, assimilates This content is only available as a PDF. © Oxford University Press

YEO, A., R.;LEE,, λ.-S.;IZARD,, P.;BOURSIER, P., J.;FLOWERS, T., J.

doi: 10.1093/jxb/42.7.881pmid: N/A

Abstract Addition of 50 mM NaCl to Oryza sativa L. had little effect upon the time of leaf initiation, but leaf mortality prior to the normal phase of senescence was increased and the onset of senescence was advanced. There was no significant effect upon the day-to-day pattern of growth, nor upon the ultimate length, of leaves that were developing at the time of, or shortly after, salinization with 50 mM NaCI. Leaves that developed after prolonged exposure of the plants to salinity were shorter. Addition of NaCl, KC1 or mannitol to the root medium brought about a cessation of leaf elongation within one minute. Growth at a reduced rate restarted abruptly after a lag period that depended upon the external concentration. Elongation rate recovered its original value within 24 h after exposure to 50 mM NaCl, though not at higher concentrations. Addition of NaCl at concentrations up to 100 mM elicited no short-term effects upon photosynthetic gas exchange. Na uptake contributed to osmotic adjustment of the growing zone. When plants were rapidly exposed to 50 mM NaCl, no change in turgor pressure was detectable in the growing zone with the resolution of the miniature pressure probe used (about 70 kPa). It is concluded that the initial growth reduction in rice caused by salinization is due to a limitation of water supply. A clear distinction is made between the initial effects of low salinity which are recoverable and the long-term effects which result from the accumulation of salt within expanded leaves. Leaf elongation, gas exchange, photosynthesis, water relations This content is only available as a PDF. © Oxford University Press

SAYED, HAMEDA, EL;KIRKWOOD, R., C.;GRAHAM, N., B.

doi: 10.1093/jxb/42.7.891pmid: N/A

Abstract The effects of incorporating a hydrogel polymer into sand on the development of selected horticultural plants grown under saline conditions has been demonstrated. In separate experiments, the seeds of tomato (Lycopersicon esculentum Mill.), lettuce (Lactuca sativa L.) and cucumber (Cucumis sativus L.) were germinated in sand/swollen hydrogel polymer mixture (25: 75, v: v) with added Hoagland nutrient solution. At cotyledon + first true leaf stage, the plantlets were transplanted into polythene growbags containing a range of sand/swollen hydrogel polymer combinations (0: 100, 25: 75, 50: 50, 75: 25 and 100: 0, v: v). Saline solutions containing NaCl, CaCl2 and MgCl2 were prepared as molar solutions and applied at combined concentrations as follows; Control (Hoagland), 2000, 4000, 8000, and 32 000 ppm. Application of the appropriate solution to the growbags was made twice per week, alternating with a comparable watering regime. Harvesting was carried out after 14 and 28 d. Polymer incorporation encouraged growth of all species under all saline conditions, the order of effectiveness of the polymer contents being as follows; 75%>50% 25% 100%>0%. At high salinity (32 000 ppm) plants of the test species were reduced in growth but appeared to be tolerant at all levels of polymer incorporation; in pure sand the level of tolerance in tomato and cucumber was <8000 ppm and in lettuce < 4000 ppm. Generally, dry weight, leaf area, succulence, chloroplast pigments (chlorophyll a, chlorophyll b, and carotenoids), photosynthetic activity, total amino acids, proline, and protein contents were increased with polymer incorporation compared with pure sand. This hydrogel polymer appears to be highly effective for use as a soil conditioner in horticulture, to improve crop tolerance and growth in a sand or light gravel substrate under saline conditions. It is intended to confirm the results of these studies by field trials. Tomato (Lycopersicon esculentum Mill.), lettuce (Lactuca sativa L.), cucumber (Cucumis sativus L.), salinity, hydrogel, polymer, salt tolerance, growth, free amino acid, free proline, and protein This content is only available as a PDF. © Oxford University Press

ANTKOWIAK,, B.;MAYER, W., E.;ENGELMANN,, W.

doi: 10.1093/jxb/42.7.901pmid: N/A

Abstract The ultradian rhythmic movement of the lateral leaflets of Desmodium motorium is accompanied by rhythmic changes of the extra- and intracellular electrical potentials in the pulvinus, which are measured in situ in the pulvinus against the bathing solution of the petiole. Extra- and intracellular potentials oscillate with 180'b0 phase difference to each other, as shown by simultaneous measurements of both types of potentials in the abaxial part of the pulvinus. Light-induced changes of these potentials move in opposite directions. The in situ membrane potential of the motor cells of the pulvinus was calculated from the difference between the extra- and intracellular potentials. It was found to oscillate between −136 and −36 mV, in phase with the intracellular and inverse to the extracellular potential. The phase relationship between the leaflet movement rhythm and the in situ membrane potential rhythm was as follows: downward movement is preceded and accompanied by a strong depolarization, upward movement by hyperpolarization. Our results suggest that membrane depolarization in pulvinar motor cells of Desmodium motorium drives and controls potassium efflux and hyperpolarization potassium influx via potassium channels. Desmodium pulvinus, leaf movement, pulvinar motor cells, electrical potential This content is only available as a PDF. © Oxford University Press