Short-term Water Stress Research Articles

Wild Oat (Avena fatua) and Spring Barley (Hordeum vulgare) Interference in a Greenhouse Experiment

Intraspecific and interspecific interference effects on growth, gas exchange, and water potential of wild oat and spring barley were measured under greenhouse conditions using a 1:1.06 barley to wild oat replacement series. Intraspecific barley interference affected barley growth more than interspecific wild oat interference. Interspecific wild oat interference with barley reduced wild oat growth more than intraspecific interference. Wild oat plant height surpassed barley plant height near barley anthesis. Growth and gas exchange of barley and wild oat responded the same to short-term water stress.

Concurrent action of salinity and water stress on leaf gas exchange and water relations in tomato

Tomato plants (Lycopersicon esculentum Mill.) grown in pots were irrigated for four weeks with 0.04,0.08,0.12 molai NaCl solutions and a control solution. Half the plants in each salt treatment were water stressed for five days. Single leaf gas exchange at near ambient C02, water consumption and plant water relations were measured. Both salt and water stress reduced growth, water potential and gas exchange rates. Well watered plants were only slightly stressed by a salt concentration of 0.04 molai, while plant growth continued at a concentration of 0.08 molai. Short-term water stress imposed greater stress than long-term salt stress; carbon exchange rate (CER) was partially limited by stomatal closure in the case of water stress and by mesophyll limitation with longer-term salinity treatments. Osmoregulation in response to salt stress did not impart particular tolerance to transient water stress.

Comparison of physiological responses of pearl millet and sorghum to water stress

Physiological responses of pearl millet and sorghum to water stress were compared for better understanding of crop adaptation in drylands. Pearl millet (MBH-110) and sorghum (CSH-6) were raised in pots and were subjected to short term water stress at anthesis stage. Water stress decreased leaf water potential, rates of stomatal conductance, photosynthesis and transpirations and transpiration efficiency in flag leaves relatively more in sorghum than in pearl millet. Stomatal conductance and transpiration rates recovered quicker in pearl millet than in sorghum in 24 h after rewatering. Dry season accentuated the water stress effects. Transpiration efficiency of pearl millet was more responsive to increase in atmospheric moisture. The physiological responses explain the better adaptation of pearl millet to drier regions than of sorghum.

Short-term water stress leads to a stimulation of sucrose synthesis by activating sucrose-phosphate synthase

The aim of this work was to identify which aspects of photosynthetic metabolism respond most sensitively to leaf water deficit. Spinach (Spinacia oleracea L.) leaf discs were floated on sorbitol concentrations of increasing molarity and changes of the protoplast volume were estimated using [(14)C]sorbitol and (3)H2O penetration. Detached leaves were also wilted until 10% of their fresh weight was lost. Photosynthesis was studied at very high external CO2 concentrations, to eliminate the effect of closing stomata. There was no large inhibition of CO2 fixation after wilting leaves, or until the external water deficit was greater than-1.2 MPa. However, partitioning changed markedly at these moderate water deficits: more sucrose and less starch was made. When an inhibition of CO2-saturated photosynthesis did appear at a water deficit of-2.0 MPa and above, measurements of chlorophyll-fluorescence quenching and metabolite levels showed the thylakoid reactions were not especially susceptible to short-term water stress. The inhibition was accompanied by a small increase of the triose phosphate: ribulose-1,5-bisphosphate ratio, showing regeneration of ribulose-1,5-bisphosphate was affected. However, there was also a general increase of the estimated concentrations of most metabolites, indicating that there is no specific site for the inhibition of photosynthesis. Increasing water deficit led to a large increase of fructose-2,6-bisphosphate. This is explained in terms of a simultaneous increase of fructose-6-phosphate and inorganic phosphate as the cell shrinks. The high fructose-2,6-bisphosphate led to the accumulation of triose phosphates, and the potential significance of this for protection against photoinhibition is discussed. There was an increase in the extractable activity of sucrose-phosphate synthase. This was only detected when the enzyme was assayed in conditions which distinguish between different kinetic forms which have previously been identified in spinach leaves. It is proposed that activation of sucrose-phosphate synthase is one of the first sites at which spinach leaves respond to a rising water deficit. This could be of importance for osmoregulation.

Suboptimal nitrogen status sensitizes the photosynthetic apparatus in willow leaves to long term but not short term water stress

The response to drought was compared for willow plants of optimal leaf nitrogen content (100 N) and those of 86% of this content (86 N). Gas exchange measurements revealed that the carboxylation efficiency (CE) of photosynthesis was more sensitive to drought than the photosynthetic capacity in both N regimes. Since the leaf content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was found to be much more resistant it is suggested that a decreased specific activity of Rubisco underlies the decreased CE. Although the rate of water consumption was the same for 86 N and 100 N plants the photosynthetic apparatus responded much more rapidly in the 86 N leaves. This increased sensitivity of 86 N leaves was not due to accelerated senescence as judged by comparison with parallel plants subjected to discontinued fertilization; the two categories of treatments resulted in the same loss of leaf nitrogen and Rubisco but drought induced a much more rapid photosynthetic depression. In contrast to the drought situation, 86 N and 100 N plants behaved similarly when compared under short term water stress. First, when single attached leaves were exposed to a sudden drop in air humidity the capacity of CO2 uptake in both N regimes decreased about 20% over 10 min while the leaf water potential remained high. Second, in freely transpiring leaf discs cut from 86 N and 100 N leaves the same relationship between capacity of O2 evolution and extent of dehydration was observed. The possible mechanisms underlying the increased susceptibility of 86 N leaves to drought is discussed; the water status of the roots not the leaves is suggested to be the determining factor.

Effect of Short-term Water Stress on Leaf Gas Exchange Processes and Plant Water Potential in Schefflera

Abstract Increasing water stress situations were imposed on Schefflera arboricola Hayata ‘Compacta’ for up to 7 days under controlled growth chamber conditions. Net CO2 exchange and transpiration rates, stomatal conductance to water vapor and xylem water potential were measured at constant temperature, photosynthetic photon flux density (PPFD), and atmospheric humidity. A strong relationship was found for transpiration and CO2 exchange process. When the water content of the substrate decreased as a result of transpiration and soil surface evaporation, both transpiration and CO2 exchange rates decreased drastically. Xylem water potential remained fairly constant during this soil moisture deficit. Following the drying cycle, efficient and fast recovery of the plants was observed.

Availability of water controls Crassulacean acid metabolism in succulents of the Richtersveld (Namib desert, South Africa)

Features of Crassulacean acid metabolism (CAM) were studied in a variety of different succulents in response to climatic conditions between March 1977 and October 1983 in the southern Namib desert (Richtersveld). A screening in 1977 and 1978 revealed that nearly all investigated succulents performed a CAM, but overnight accumulation of malate declined gradually with decreasing soil water potential, tissue osmotic potential, and leaf water content. This was further substantiated by an extended period of insufficient rainfall in 1979 and 1980 which damaged the evergreen CAM succulents between 80 and 100%. In most of the species still living, neither CO2-gas exchange nor diurnal acid fluctuation, indicative of CAM, could be detected unless an abundant rainfall restored both CAM features. Plants persisted in a stage of latent life.Water supply is one necessary prerequisite for CAM in the Richtersveld. But even well-watered plants with CAM were sensitive to short-term water stress caused by high water-vapour partialpressure deficit (VPD) in the night, which reduced or prevented CO2 uptake and resulted in a linear relation between overnight accumulated malate and VPD. The results do not support the opinion that, for the Namib succulents, CAM is an adaptive mechanism to water stress since long-term and short-term water stress stopped nocturnal malate synthesis, but instead lead to the conclusion that nocuturnal CO2 fixation is only performed when the water status of the plant can be improved simultaneously.

Effect of water stress on photosynthesis and in vitro activities of the PCR cycle enzymes in pigeonpea (Cajanus cajan L.)

Leaf water potential was decreased by withholding irrigation to provide three levels of stress described as mild ({ie69-1}) moderate ({ie69-2}) and severe ({ie69-3}). The specific activity of NADP linked glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, aldolase, phosphogluco-isomerase and RuBP carboxylase decreased under mild stress, but the activity of phosphoglucomutase showed an increase whilst ribulose-5-phosphate kinase was least affected. With further decrease in water potential, the activity of NADP linked glyceraldehyde-3-phosphate dehydrogenase and aldolase showed a decrease, whereas, the activities of fructose-1,6-bisphosphatase, phosphoglycerate kinase, phosphogulcomutase and RuBP carboxylase increased. Net CO2 fixation decreased sharply with stress, whereas, respiration and photorespiration increased in moderate stress, but decreased under severe stress. Stomatal resistance also increased with decrease in water potential. It seems that in vitro enzyme activities of PCR cycle are not responsible for decreased photosynthesis in pigeonpea under short term water stress.

Effects of partial defoliation, changes of irradiance during growth, short-term water stress and growth at enhanced p(CO2) on the photosynthetic capacity of leaves of Phaseolus vulgaris L.

The response of CO2-assimilation rate to the intercellular partial pressure of CO2 (p(CO2)) is used to analyse the effects of various growth treatments on the photosynthetic characteristics of P. vulgaris. Partial defoliation caused an increase in CO2-assimilation rate at all intercellular p(CO2). A change in the light regime for growth from high to low light levels caused a decrease of CO2-assimilation rate at all intercellular p(CO2). Growth in a CO2-enriched atmosphere resulted in lowered assimilation assimilation rates compared with controls at comparable intercellular p(CO2). Short-term water stress initially caused only a decline in the CO2-assimilation rate at high intercellular p(CO2), but not at low intercellular p(CO2). Except under severe water stress, changes in the initial slope of the response of CO2-assimilation rate to intercellular p(CO2) were in parallel to those of the in-vitro activity of ribulose-1,5-bisphosphate (RuBP) carboxylase. From the results, we infer that partial defoliation, changes in the light regime for growth, and growth in a CO2-enriched atmosphere cause parallel changes in RuBP-carboxylase (EC 4.1.1.39) activity and the "capacity for RuBP regeneration", whereas short-term water stress initially causes only a decline in the RuBP-regeneration capacity.

CO2 exchange of CAM exhibiting succulents in the southern Namib desert in relation to microclimate and water stress

The responses of CO2 exchange and overnight malate accumulation of leaf and stem succulent CAM-plants to water stress and the particular climatic conditions of fog and föhn in the southern Namib desert have been investigated. In most of the investigated CAM plants a long term water stress gradually attenuated any uptake of external CO2 and led to CO2 release throughout day and night. No CAM-idling was observed. Rainfall or irrigation immediately restored daytime CO2 uptake while the recovery of the nocturnal CO2 uptake was delayed. Dawn peak of photosynthesis was only found in well watered plants but was markedly reduced by the short term water stress of a föhn-storm. Morning fog with its higher diffuse light intensity compared with clear days increased photosynthetic CO2 uptake considerably. Even in well watered plants nocturnal CO2 uptake and malate accumulation were strongly affected by föhn indicating that the water vapour pressure deficit during the night determines the degree of acidification.

CO2 exchange of CAM exhibiting suceulents in the southern Namib desert in relation to microclimate and water stress

The responses of CO2 exchange and overnight malate accumulation of leaf and stem succulent CAM-plants to water stress and the particular climatic conditiens of fog and föhn in the southern Namib desert have been investigated. In most of the investigated CAM plants a long term water stress gradually attenuated any uptake of external CO2 and led to CO2 release throughout day and night. No CAM-idling was observed. Rainfall or irrigation immediately restored daytime CO2 uptake while the recovery of the noctural CO2 uptake was delayed. Dawn peak of photosynthesis was only found in well watered plants but was markedly reduced by the short term water stress of a föhn-storm. Morning fog with its higher diffuse light intensity compared with clear days increased photosynthetic CO2 uptake considerably. Even in well watered plants noctural CO2 uptake and malate accumulation were strongly affected by föhn indicating that the water vapour pressure deficit during the night determines the degree of acidification.

The Response of Oxygen and Carbon Dioxide Exchanges and Root Activity to Short Term Water Stress in Soybean

The gross and net 02 evolution together with 02 uptake, C02 assimilation, transpiration, shoot dark respiration, root respiration and ion uptake of a soybean plant were studied during 19 d which included two periods of water stress. 02 uptake was measured using 1802 as a tracer. Short term water stress induced immediate and lasting effects: (1) reduction of light interception by wilting, (2) limitation of the total reducing equivalent produced by the electron transport chain, (3) decrease of stomatal conductance reducing both losses of water and the entry of C02 for assimilation, (4) relative stimulation of 02 uptake. The ratio of 02 uptake to C02 assimilation changed from 1 -0 before stress to 1 -4 for several days after. Root respiration was less affected by the stress than ion uptake and shoot gas exchanges.

The Involvement of Water Stress and Ethylene in Senescence of Cut Carnation Flowers

Exposing cut carnation (Dianthus caryophyllus, cv. White Sim) to short term (12 h) water stress resulted in a marked increase in the water saturation deficit (WSD) of the petals. Full recovery occurred upon transfer of the flowers to water in humid conditions (r.h. 85%). However, an increase in aminocyclopropane carboxylic acid (ACC) content occurred immediately upon stress. An associated rise in ethylene production following transfer to humid conditions was observed earlier than in the control. Exogenous ethylene, applied alone or in combination with water stress, increased the WSD of the petals. Continuous treatment of cut flowers with amino-oxyacetic acid (AOA), a known inhibitor of ACC synthesis, suppressed ethylene production, delayed the rise in WSD which accompanied development and senescence and hence delayed wilting. Similar results were obtained with short term (2 h) treatment with AOA prior to stressing the flowers. Short term AOA treatment partially inhibited the rise in WSD during the stress period. On the basis of our findings, in particular that no rise in ethylene production occurred during water stress, it is suggested that the effect of water stress is not directly mediated by ethylene. The possible modulatory effect of water stress and AOA on certain characteristics of the petal cell membrane is discussed.

The effect of a water stress on the cold hardiness of winter wheat

Crowns of winter wheat plants water stressed with polyethylene glycol (PEG) (molecular weight 20 000) prior to hardening were more cold hardy than tender crowns or crowns hardened for 2 days (p ≤ 0.05). After 16 days of hardening, plants from all treatments reached the same level of hardiness. Winter wheat crowns water stressed with PEG (210 g/L) for either 0,5, or 21 days reached the same level of hardiness after 2 days of acclimation. In both short- and long-term stress studies, the crown moisture content of the stressed plants was lower (p ≤ 0.05) than that of the controls prior to acclimation. With increasing hardiness both leaf osmotic potential and crown moisture content decreased (p ≤ 0.05). Short-term water stress also resulted in an increase in sugars, specifically sucrose (p ≤ 0.05) prior to cold hardening. However the total sugar content did not parallel the increase in hardiness.Changes in several metabolic parameters were also considered. Significant correlations were found in both studies between the LT50 and osmotic potential, moisture content, and dry weight. Most of the variability in LT50 could be explained by changes in leaf osmotic potential and crown moisture content.

Membrane potentials and salt distribution in epidermal bladders and photosynthetic tissue of Mesembryanthemum crystallinum L.

Abstract Membrane potentials (pd's) of epidermal bladder cells and green leaf cells of Mesembryanthemum crystallinum L. are rather low (between −10 and −40 mV). During growth on 400 mM NaCl membrane potentials decrease further. As shown previously, plants grown on 400 mM NaCl show the diurnal changes of malate levels typical for plants having crassulacean acid metabolism. Therefore, in this study membrane potentials were measured at different times of the day, but no diurnal variations of pd were correlated with diurnal oscillations of malate levels. Resting potentials are similar in bladder cells and in green leaf cells and are similar in continuous light and darkness. Both bladder and leaf cells display light‐triggered photosynthesis‐dependent oscillations of the membrane potential although the bladder cells do not appear to be photosynthetically very active. This suggests electrical coupling between the bladder cells and the underlying green cells. Over a larger distance (2 mm) in the leaves, however, there is no direct evidence for electrical coupling. Cl−, Na+, and K+ concentrations are similar in bladder cells and in the photosynthetically active tissue of leaves and stems. Bladder cells appear to contain high concentrations of free oxalate. The present findings corroborate earlier conclusions that the epidermal bladder cells of M. crystallinum function as peripheral water reservoirs providing protection from short term water stress.

Influence of Water Stress on Water Relations and Growth of a Tropical (C4) Grass, Panicum maximum var. trichoglume

The effects of recurring cycles of short-term water stress on the water relations and growth of P. maximum var. trichoglume in pots of soil were investigated under controlled conditions. As soil water content decreased there was an increase in the resistance to water movement in the soil-plant system. Leaf stomatal resistance increased and concomitantly transpiration rate decreased when soil water content fell below 37 % (soil water potential of - 1 .0 bars) and leaf water potentials were less than - 6 bars. The leaf water potential at wilting (- 8 to - 10 bars) and the relation between leaf water potential and relative water content changed with leaf position on the tiller. The death of early-formed leaves on the plants was accelerated by water stress but, in contrast, the later-formed leaves died more rapidly in the control (unstressed) treatment so that finally the control plants had a higher proportion of dead leaves. Plant growth was reduced at soil water contents above the permanent wilting point. Reduction in net assimilation rate was the main determinant of lower relative growth rate of stressed plants over the initial cycles of stress but subsequently, as leaf area expansion was reduced, leaf area ratio also had a significant influence. Water stress influenced growth directly, and also indirectly via its effect on plant development (ontogeny). Two techniques were used to separate the direct from the indirect effects on relative growth rate Some published data which suggest a stimulation of growth rate after the relief of stress are re-interpreted and the effect is shown to be due mainly to differences in ontogeny between stressed and control treatments

Corn plant comparative reactions to artificial dehydration

Aim. There are maize plants of inbred line L-370 (control) and from T4 progeny of plants transformed via in planta Agrobacterium-mediated transformation with LBA4404 strain harboring pBi2E with double-stranded RNA-suppressor of the proline dehydrogenase gene. The free proline and sucrose levels, sucrose/fructose ratio during period of desicca-tion/rehydration were investigated. Methods. Maize T4 progeny and initial plants of L-370 line were cultivated in con-tainers. Variants were tested under short term (4 days) dehydration and after 3.5 hours of rehydration. The free proline and carbohydrates levels were estimated at those times of the experiment. Results. The short-term water deficit did not create pathological changes in plants. But the free proline levels rose in leaves of all variants. At the same time the ami-no acid levels under stress condition in T4 plans were higher than in L-370-plants. After 3.5 hours of rehydration the proline content in control plants decreased and stayed without changes in T4 plans. In T4 plants the carbohydrate meta-bolism systems energy maintained the stability of the sucrose/fructose ratio during the whole time of experiment. Conclusions. The T4 plants high level of water stress tolerance is a possible result of transgene activity.Keywords: Zea mays, Agrobacterium-mediated transformation, T4-progeny, short-term water stress, dehydration, proline sucrose.