Relief Of Water Stress Research Articles

Compensatory Growth Responses During Reproductive Phase of Cowpea after Relief of Water Stress

AbstractUnpredictable drought affects growth and yield of dryland cowpea (Vigna unguiculata [L.] Walp.) during rainy season. With the objective of identifying compensatory growth responses after relief of water stress, pot‐grown plants (cv. C‐752) were water‐stressed at flowering, and physiological responses, short term dry matter partitioning upon relief of water stress, and productivity at maturity were studied. Water stress decreased, to varying degrees, leaf water potential, stomatal conductance, photosynthesis rate and transpiration rate. Recovery in assimilation lagged behind that in water relations. Assimilate supply seemed to be limiting early pod growth upon relief of water stress due to low photosynthesis rate, reduced leaf area per pod, and increased partitioning to leaf expansion. However, later pod growth was not limited by assimilate supply and final dry matter per pod was similar in both non‐stressed and stress‐affected plant. Cowpea exhibited the following growth responses during pod‐fill stage upon relief of water stress: 1. increase in leaf area, 2. shift in dry matter partitioning in favour of leaf expansion, 3. extended green leaf duration, and 4. increase in pod number. These partially compensating physiological responses probably ensure reasonable productivity of dryland cowpea during rainy season.

Observations on the effects of relief of late water stress in potato

Experiments on crops of three cultivars of potato showed the effects of the relief of water stress towards the end of the growing season. Treatments imposed showed the starting condition and the responses of crops which were actively growing, newly had their tops removed, or were without active roots.

The effect of plant-hormone pretreatments on ethylene production and synthesis of 1-aminocyclopropane-1-carboxylic acid in water-stressed wheat leaves

Excised wheat (Triticum aestivum L.) leaves, when subjected to drought stress, increased ethylene production as a result of an increased synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) and an increased activity of the ethyleneforming enzyme (EFE), which catalyzes the conversion of ACC to ethylene. The rise in EFE activity was maximal within 2 h after the stress period, while rehydration to relieve water stress reduced EFE activity within 3 h to levels similar to those in nonstressed tissue. Pretreatment of the leaves with benzyladenine or indole-3-acetic acid prior to water stress caused further increase in ethylene production and in endogenous ACC level. Conversely, pretreatment of wheat leaves with abscisic acid reduced ethylene production to levels produced by nonstressed leaves; this reduction in ethylene production was accompanied by a decrease in ACC content. However, none of these hormone pretreatments significantly affected the EFE level in stressed or nonstressed leaves. These data indicate that the plant hormones participate in regulation of water-stress ethylene production primarily by modulating the level of ACC.

Abscisic acid and after-effects of water stress in pearl millet ( Pennisetum americanum (L.) Leeke)

The involvement of abscisic acid (ABA) in stomatal regulation of pearl millet ( Pennisetum americanum (L.) Leeke) following the relief of water stress, was investigated in two types of experiment. In the first, stress was induced by severing the shoot from the root system, while in the second, intact plants were gradually stressed by withholding water and regulating vapour pressure deficit. Changes in water potential (ψ), ABA content, and stomatal conductance were determined for both groups of plants following rewatering. Intact plants attained lower leaf ψ and accumulated more ABA prior to rewatering than did detached shoots. Water potentials increased to equal those of untreated plants 3 h after supplying water to detached shoots and about 7 h after rewatering intact plants. ABA levels continued to increase in leaves on detached shoots during the first hour after supplying water, but no such effect occurred with intact plants. Following this ‘overshoot’, ABA levels in detached shoots declined rapidly, attaining control values within a further 2 h. In intact plants ABA decreased to control levels 8 h after rewatering. Stomatal conductances increased shortly after rewatering in both groups of plants and in detached shoots opening occurred at a time when ABA levels were still increasing. While conductances recovered to control values within 3–4 h in detached shoots, in intact plants conductances failed to recover completely even 48 h after rewatering.

Growth of ‘Grasslands Nui’ ryegrass after water and high temperature stress

In cortrolled-environment experiments, ‘Grasslands Nui’ ryegrass (Lolium perenne L.) was held at —900 kPa leaf water potential for 14 days at 30°/25°c(day/night) and growth recovery was measured 14 days after relief of water stress at 20°/15°c. One experiment was a comparison with a lower temperature (20°/15°c) during water stress; two experiments compared effects of clipping all leaf, one of these at a greater stress of —2100 kPa leaf potential. At 30°c compared with 20°c there were no marked treatment differences; weight of living leaf tissue was unchanged during water stress, and weight of stem-plus-root tissues increased and numbers of tillers were unchanged. New leaf growth over a 7-day period after relief of water stress showed no significant effect of the previous treatment. Mean rate of leaf growth over 14 days from relief of water stress was lower for the previous 30°c treatment. In one experiment, where all leaf was clipped just before water stress, growth of stem-plus-root tissues during water ...

Evaluation of Free Proline Accumulation as an Index of Drought Resistance Using Two Contrasting Barley Cultivars1

The two barley [Hordeum vulgare L.] cultivars, ‘Proctor’ and ‘Excelsior’, differ in their stability of grain yield under dryland conditions; Proctor produces a low yield in drought seasons and Excelsior a relatively high yield. This varietal difference in drought resistance was clearly expressed at the three to four‐leaf stage, both in soil‐grown plants in greenhouse tests and in perlite‐grown plants in growth chamber experiments. Water deficits were imposed either by withholding water from the soil, or by flooding the perlite rooting medium with polyethylene glycol 6000 (PEG) of osmotic potential –19 bars. Under both conditions the drought‐susceptible Proctor sustained more severe leaf kill than the resistant Excelsior.Leaf water potentials (ψleaf) and free proline concentrations in various zones of the second leaf blade were determined during the development of PEG‐imposed stress. In both cultivars, a gradient of decreasing ψleaf was established from the base to the tip of the blade; a ψleaf value lower than –30 to –40 bars in any leaf zone indicated leaf kill, i.e. failure of that zone to recover on relief of stress. The ψleaf at the mid‐blade zone always fell more rapidly in Proctor than in Excelsior, and consequently reached the critical –30 to –40 bar value earlier. In both varieties, free proline accumulated in leaf tissue as ψleaf fell, and reached the highest concentration as leaf kill became severe; at this stage much of the free proline was localized in the non‐viable leaf zone. Under stress, Proctor leaves always accumulated free proline more rapidly than Excelsior leaves. On relief of water stress, free proline levels declined in viable leaf tissue, but remained very high in the drought‐killed, desiccated leaf zone.These data demonstrate that reports of a simple positive correlation between proline‐accumulating potential and drought resistance in barley may be in error. Therefore, proline‐accumulating potential should not be utilized as a positive index of drought resistance in screening methods for cereal breeding programs.

Shoot growth inCoffea arabicaL., Π Growth flushing stimulated by irrigation

SummaryThe growth activity of axillary and terminal vegetative apices of Coffea arabica trees was compared when growing in the field in Kenya under carefully controlled soil moisture regimes in which the trees were irrigated weekly, or when irrigation and rainfall were withheld for different periods and at different times during the hot dry season; the effect of the treatments on internal water stress was studied using a stomatal infiltration technique. Weekly irrigation to maintain the soil beneath trees near to field capacity failed to relieve water stress measured during the day, indicating that the evaporative demand of the atmosphere plays a larger part than soil moisture in determining the water status of the tree. However, trees irrigated after eight weeks’ enforced drought flushed immediately, producing leaves faster and opening their stomata during the day to a greater extent than trees which had been regularly irrigated. Trees which experienced twelve weeks enforced drought produced approximatel...

The course and magnitude of water stress in Lolium perenne and Dactylis glomerata

SUMMARYSimulated swards of Dactylis glomerata (var. S.37) and Lolium perenne (var. S.23) were grown in large lysimeters or vertical pipes of 15 cm diameter, both sufficiently deep to allow largely unrestricted root development.Rainfall was excluded, and the effect of a drying cycle on the plant water balance was compared with irrigated controls in a sequence of sampling harvests at increasing soil water deficits.Leaf water potential (ΨL) fell during the day, both in treatments and controls, to levels which might be expected to reduce extension growth and, frequently, stomatal diffusion. Rapid recovery occurred in the evening to levels which might allow normal functioning of growth processes not dependent on sunlight. Defoliation reduced plant stress and stomatal restriction.The amelioration of plant water stress appeared to require a reduction in atmospheric evaporative demand, and irrigation had relatively little effect. The possibility is discussed that the major benefits of irrigation are other than through the relief of water stress within the plant. The significance of this is considered in relation to conventional irrigation techniques.The leaf water status was more sensitive to drought, transpiration was reduced more, and the root system extended more slowly in Dactylis than in Lolium. Consequently, the onset of permanent wilting due to exhaustion of water from the profile was delayed compared with Lolium. It is deduced that this characteristic might enhance the survival of Dactylis in prolonged drought, but prove disadvantageous in terms of growth during short droughts, when reduced stomatal opening might limit CO2 uptake. This would not be an impediment, however, if investigations suggesting that partial closure has a minor effect on CO2 uptake compared with that on transpiration were to be confirmed.