Influence of Xylem Water Potential on Leaf Elongation and Osmotic Adjustment of Wheat and Lupin

The leaf elongation rate and osmotic pressure at full turgorof wheat (Triticum aestivum L.) and lupin (Lupinus cosentiniiGuss.) were measured in well watered plants, in plants thatwere allowed to dry the soil slowly over 7 d, and in plantsin which the water potential of the leaf xylem was maintainedhigh by applying pressure to the roots during the drying cycle.Maintenance of high xylem water potentials failed to preventa reduction in the rate of leaf elongation as the soil dried,while the osmotic pressure at full turgor and the degree ofosmotic adjustment increased as the soil water content decreased.The rate of leaf elongation was reduced more and the degreeof osmotic adjustment was higher in leaves with high xylem waterpotentials than in those in which leaf xylem potentials wereallowed to decrease as soil water content decreased. Osmoticadjustment was linearly correlated with the reduction in leafelongation rate in both wheat and lupin. Key words: Osmotic adjustment, leaf elongation, turgor regulation     

Comparison of Osmotic Adjustment Responses to Water and Temperature Stresses in Spring Wheat and Sudangrass

This study explores the mechanisms of osmotic adjustment bycomparing the growth of spring wheat and sudangrass, which exhibitdifferent degrees of osmotic adjustment, under soil water andtemperature stresses. Leaf water potential ( ₁), osmotic potential(), and rate of leaf area growth of spring wheat and sudangrassseedlings were measured at combinations of five soil water potentials,from -0·03 to -0·25 MPa, and six root temperatures,from 14 to 36°C. Spring wheat exhibit little osmotic adjustment.The leaf osmotic potential was not affected by either soil wateror root temperature stress. Osmotic potential of sudangrassdecreased in parallel with the decreasing leaf water potentialas a result of osmotic adjustment. As soil water potential decreasedfrom -0·03 to -0·25 MPa, the rates of growth andphotosynthesis of spring wheat both decreased by about 30%.For sudangrass with the same range of soil water potential,the photosynthesis rate decreased by only 10% while the leafarea growth rate decreased by 49%. We introduce a dimensionlessindex (R) to quantify the degree to which environmental stressesalter the balance between production of photosynthates and theiruse for growth. The index, R, is equal to 1 when stress reducesgrowth and photosynthesis by the same degree, i.e. the balancebetween production and consumption of photosynthate is not disturbed.R is smaller than 1 when growth is reduced more than photosynthesis.R was equal to 1 for spring wheat where there was no osmoticadjustment. For sudangrass, R decreased from 1 to 0·25as osmotic potential decreased from -1·10 to -1·63MPa. These findings lead to the hypothesis that osmotic adjustmentcould result from an imbalance between production, consumptionand translocation of photosynthates under stressed conditions.Copyright1993, 1999 Academic Press Osmotic adjustment, water stress, root temperature     

The Extent and Pattern of Osmotic Adjustment in White Clover (Trifolium repens L.) During the Development of Water Stress

White clover plants were subjected to water stress followingthe cessation of watering. As a water deficit developed, waterand osmotic potentials were measured in stolon tips, leavesfrom the stolon tip and leaves from the plant crown. Pressurepotentials were calculated. Pressure potential was maintainedin stolon tips even when water potential fell to around –2·0MPa. In contrast, pressure potential in leaves fell rapidlyas water stress developed. Total amino acid and potassium levels were largely unaffectedin both stolon tips and leaves. Water-soluble carbohydratesand proline accumulated during water stress. The increase inproline level in leaves did not follow the same pattern as thatin stolon tips, although toward the end of the water stressperiod the level had increased by a similar extent in both partsof the plant. Additionally, pressure potential and osmotic potentialappeared to be significantly related to proline content in stolontips. No such relationship was found for leaves. The role ofproline in osmotic adjustment is discussed. Trifolium repens L. cv. Olwen, white clover, water stress, osmotic adjustment, proline     

The Effect of Grain Number per Ear (Sink Size) on Source Activity and its Water-Relations in Wheat

Blum, A., Mayer, J. and Golan, G. 1988. The effect of grainnumber per ear (sink size) on source activity and its water-relationsin wheat.–J. exp. Bot. 39: 106–114. Work was done to evaluate the nature of sink-source relationshipsin wheat (Triticum aestivum L.), when the strength of the sinkwas modified by the removal of half of the grain from the earat about anthesis. The main hypothesis was that sink-sourcerelationship would be modified by water stress and that a weakersink would improve the drought resistance of the source. Two experiments were performed. The first experiment evaluatedthe effect of de-graining in two wheat varieties grown in thefield. The second experiment (in the greenhouse) evaluated theeffect of de-graining in plants subjected to water stress afteranthesis by immersing the root system in a solution of polyethyleneglycol (6000), as compared with non-stressed controls. In bothexperiments measurements were performed after de-graining toprovide data on leaf gas exchange, leaf water potential, osmoticadjustment of leaves and ears (greenhouse), the percent of stemweight loss as an index of stem reserve mobilization, finalroot weight (greenhouse) and ear weight components. De-graining caused a decrease in flag leaf stomatal conductance,carbon exchange rate (CER) and transpiration and an increasein flag leaf water potential. These effects were stronger withwater stress. De-graining did not affect osmotic adjustmentin the flag leaf but induced better adjustment in glumes andawns. De-graining decreased the percent of stem weight lossand increased final root weight, especially under drought stress. A weaker sink was, therefore, considered to improve plant droughtresistance in terms of the maintenance of higher leaf waterpotential, a larger root, a better osmotic adjustment in theear and, possibly, increased flag leaf longevity. The ‘cost’of this improved drought resistance was in reduced flag leafCER and reduced stem (and root?) reserve mobilization. Key words: Drought resistance, carbon exchange rate, stomata, transpiration, osmotic adjustment, leaf water potential, root, awns, yield     

Leaf Water Relations, Osmotic Adjustment, Cell Membrane Stability, Epicuticular Wax Load and Growth as Affected by Increasing Water Deficits in Sorghum

A field experiment was conducted with a non-irrigated waterstress treatment and an irrigated control using four sorghum(Sorghum bicolor L. Moench) cultivars. We investigated the effectsof water deficits on leaf water relations, osmotic adjustment,stomatal conductance, cuticular conductance, cell membrane stability(CMS) measured by the polyethylene glycol (PEG) test, epicuticularwax load (EWL), cytoplasmic lipid content, solute concentrationin cell sap, and growth. Osmotic adjustment was observed under water deficit conditions.Lower osmotic potential enabled plants to maintain turgor anddecreased the sensitivity of turgor-dependent processes. Sugarand K were identified as the major solutes contributing to osmoticpotential in sorghum. Sugar and K concentrations in cell sapincreased by 37·4% and 27%, respectively, under waterdeficit conditions in favour of decreasing osmotic potential.Stomatal conductance and cuticular conductance were lower inthe non-irrigated plants. A wide range in CMS among four cultivarswas observed. CMS increased with increasing water deficits.EWL increased on leaves of water deficient plants and was positivelycorrelated with cuticular conductance and CMS. Membrane phospholipidcontent increased in water-stressed plants. CMS as measured by the PEG test, was influenced by EWL, cuticularthickness, and osmotic concentration of leaf tissues. The cultivarswhich maintained higher CMS, higher EWL, lower cuticular conductance,higher turgor and higher osmotic adjustment under water deficitconditions were identified as drought tolerant. Key words: Sorghum bicolor, cell membrane stability, leaf water relationsosmotic adjustment, water stress     

Salt Tolerance in the Triticeae: Growth and Solute Accumulation in Leaves of Thinopyrum bessarabicum

Gorham, J., McDonnell, E., Budrewicz, E. and Wyn Jones, R. G.1985. Salt tolerance in the Triticeae: growth and solute accumulationin leaves of Thinopyrum bessarabicum.—J. exp. Bot. 36:1021–1031. The diploid wheatgrass Thinopyrum bessarabicum was found towithstand prolonged exposure to 350 mol m^–3 NaCl in hydroponicculture. During the gradual addition of salt to the externalmedium, osmotic adjustment was rapidly achieved by the accumulationof Na and Cl. Following osmotic adjustment constant leaf Naand Cl concentrations were maintained, and K was retained ata high level. Thinopyrum bessarabicum may be described as anosmoconformer, adjusting its internal osmotic pressure to 400–500mOsmol kg^–1 above that of the external medium in hydroponicculture. Both slower shoot initiation and reduced leaf lengthcontributed to the reduced growth rates at higher salinities.Leaf width was not affected. Increasing salinity resulted inincreases in leaf concentrations of phosphate, glycinebetaine,sucrose and proline, and in decreases in the concentrationsof nitrate, sulphate, magnesium, calcium, total amino acidsand organic acids. Thinopyrum bessarabicum exhibits salt tolerancecharacters which may be useful in wheat breeding. Key words: Salt stress, solute accumulation, osmotic adjustment, Thinopyrum     

Water Content-Potential Relationship in Soya Bean: Changes in Component Potentials for Mature and Immature Leaves under Field Conditions

Changes in turgor and osmotic potentials of soya bean leaves(Glycine max.) with changes in water content were measured throughouta season using the pressure-volume technique. Two distinct reponsesto water loss were found. When water was expressed from leavesin the pressure chamber their osmotic behavior was describedby a concentration effect based on the osmotic volume. The osmoticfraction of the total water content averaged 0·72 and0·84 for mature and immature leaves, respectively. Thechanges in turgor pressure in the chamber were described bya volumetric modulus of elasticity which increased linearlywith turgor pressure. The changes in total potential at highturgor pressures were almost exclusively due to changes in turgordue to the high modulus (high tissue rigidity) in that range.Responses were different, however, for leaves drying in thefield. For these, the osmotic changes were always large anddominated by solute adjustment. Diurnal changes in osmotic potentialwere as much as 5 bars (500 kPa), or around 50 per cent, andwere about the same magnitude as the changes in turgor pressurefor both mature and immature leaves. The elastic modulus atthe time of sampling showed the normal turgor dependence forimmature leaves but for mature leaves the initial modulus wasapparently constant at about 180 bars. The different behaviourin the pressure bomb and the field is interpreted in terms ofa rate dependence for turgor and osmotic response to water loss.     

小麦叶片光合作用与其渗透调节能力的关系

在缓慢干旱条件下,小麦叶片渗透调节能力在一定范围内随胁迫程度的加剧而增加,而在快速干旱下,渗透调节能力丧失。小麦叶片通过渗透调节使光合速率和气孔导度对水分胁迫的敏感性降低,叶片维持较高的电子传递能力、RuBP羧化酶活性和叶绿体光合能量转换系统活性,并推迟了小麦叶片光合速率受气孔因素限制向叶肉细胞光合活性限制转变的时间。     

Effects of Mineral Nutrition on Water Status and Osmotic Adjustment in Spring wheat under Different Moisture Conditions

The Ψw and RWC of the leaves of spring wheat at low level of nutrition were higher than those of the spring wheat leaves at high level during the slow drought period. Therefore, the plants at high nutrition level were more sensitive to drought. High mineral nutrition did not enhance the maximum osmotic adjustment but changed the regulatory process of osmotic adjustment under drought condition. During moderate to nearly severe drought period higher osmotic adjustment was shown in the leaves of spring wheat at high nutrition level. The major solute contributed to osmotic adjustment in the leaves of the spring wheat was soluble sugar, mostly reducing sugar.     

Turgor Maintenance by Osmoregulation inBrassica napusandB. junceaunder Field Conditions

Indian mustard (Brassica juncea(L) Czernjacw) maintains higherleaf turgor than canola (B. napusL.) under water deficits andthis is related to the greater yield of mustard under theseconditions. The work reported in this paper was designed tostudy the way mustard maintains this turgor advantage. It wasbased on three field experiments that each used at least twocultivars or lines of each species. The leaf water potentialat which leaves reached zero turgor was consistently lower inmustard than in canola (up to 1.1 MPa lower). This differencearose from a greater rate of decline in leaf osmotic potentialwith declining water potential in mustard rather than from anydifference in the osmotic potential at full turgor. Calculationsof solute accumulation showed that mustard had a greater capacityto osmoregulate than canola, with this capacity being the basisfor its advantage in turgor maintenance. Other differences inplant water relations were consistent with the differences inosmoregulation, with the predicted relative water content ofleaves at an osmotic potential of -2.5 MPa being 0.43 for canolaand 0.61 for mustard. Mustard's greater capacity to accumulatesolutes is concluded to be a major factor in its greater yieldunder water deficits. Brassica napusL.; Brassica juncea(L) Czernjacw; Indian mustard; canola; water deficit; plant water relations; osmoregulation; osmotic adjustment; turgor     

Osmotic Adjustment and Stomatal Response to Water Deficits in Maize

A pot experiment was carried out using five maize {Zea maysL.) cultivars under three soil moisture levels (MPa 0 to –0.05,–0.3 to –0.9 and –1.2 to –1.5) to investigatethe effects of water deficits on osmotic adjustment and stomatalconductance. The degree of leaf rolling and the sugar and nutrientconcentrations in leaf cell sap were measured. Leaf water potential and osmotic potential decreased and stomatalconductance decreased with increasing water deficits. Stomatalconductance correlated positively with leaf water potentialand osmotic potential. Degree of leaf rolling was lower in cultivarswhich maintained higher turgor. Osmotic adjustment of 0.08 to0.43 MPa was found under the lowest soil moisture level in fivecultivars used. Sugar and K were the major osmotic substancesin the maize plant. Sugar, K and Mg concentrations increasedunder water deficit, and correlated negatively with a decreasein osmotic potential. Key words: Zea mays L., leaf water relations, leaf rolling, osmotic adjustment, stomatal conductance, water deficit     

抗旱性不同的小麦叶片的渗透调节与水分状况的关系

两年的试验结果表明：在土壤水分胁迫下抗旱性强的小麦品种叶片的相对含水量和水势均高于抗旱性弱的品种;渗透势与水势为线性关系,水势每变动一个单位,渗透势变动0.71- 0.93个单位;渗透势与相对含水量的对数化关系为两条直线组成的一条折线,第一条直线渗透势的下降完全由渗透调节引起;第二条直线渗透势下降主要是细胞失水浓缩的结果。渗透调节能力为：秦麦3号>昌乐5号>山农587>济南13>烟农15>鲁麦5号。     

Changes in Internal Water Relations and Osmotic Properties of Leaves in Maturing Soybean Plants

The changes in the internal water relations of soybean (Glycinemax L. Merr.) leaves during vegetative and reproductive growthwere studied by following the changes in the pressure-volumecurves of soybean leaves. The results demonstrate that soybeanleaves undergo a change in their osmotic properties which coincideswith the onset of active reproductive growth and is not inducedby water stress. The observed osmotic changes resulted in anincrease in the leaf relative water content at any given bulkleaf water potential. The volume of leaf water loss needed toreduce turgor potential to zero did not change following thischange in osmotic properties. The degree of turgor maintenanceafter the change in osmotic properties depended on the abilityto maintain adequate leaf relative water content. The observedchanges in bulk osmotic potential of the soybean leaves wouldcontribute to increased leaf-soil water potential gradientsand therefore to improved ability to extract the remaining soilwater as the season progressed.     

土壤缓慢脱水对开花期小麦根系及叶片渗透调节及渗透调节物质的影响

以抗旱性不同的小麦品种为材料,在小麦的水分临界期开花期进行缓慢脱水处理,分别在脱水的不同阶段取样测定叶片及根系的渗透调节能力及渗透调节物质。结果表明：随着土壤含水量的降低,叶片与根系的饱和渗透势同步下降,表现出叶片与根系对水分胁迫反应的一致性,但根系的渗透调节能力低于叶片。根系与叶片的渗透调节物质,一方面在物质总含量方面,表现出与渗透调节能力的一致性,另一方面各种物质的相对含量又有一定差异,叶片中可溶性糖与K+的含量及增加量都高于根系,而根系中的游离氨基酸与Ca2+的相对增加量则大于叶片。     

土壤缓慢脱水对开花期小麦根系及叶片渗透调节及渗透调节物质的影响

以抗旱性不同的小麦品种为材料,在小麦的水分临界期开花期进行缓慢脱水处理,分别在脱水的不同阶段取样测定叶片及根系的渗透调节能力及渗透调节物质。结果表明：随着土壤含水量的降低,叶片与根系的饱和渗透势同步下降,表现出叶片与根系对水分胁迫反应的一到场生,但根系的渗透调节能力低于叶片。根系与叶片的渗透调节物质,一方面在物质总含量方面,表现出与渗透调节能力的一致性,另一方面各种物质的相对含量又有一定差异,叶片中可溶性糖与K＋含量及增加量都高于根系,而根系中的游离氨基酸与Ca^2 的相对增加量则大于叶片。     

Growth Rate and Water Relations of Citrus Leaf Flushes

Growth rates of seasonal leaf flushes of ‘Valencia’orange [Citrus sinensis (L.) Osbeck] were measured and waterrelations characteristics of young (new) and over-wintered (old)citrus leaves were compared. New flush leaves had lower specificleaf weights and lower midday leaf water potentials than comparablyexposed old leaves. Spring and summer flush new leaves had higherosmotic potentials than old leaves. These differences becamenon-significant as the new leaves matured. During summer conditions,water-stressed new leaves reached zero turgor and stomatal conductancealso began to decrease in them at higher leaf water potentialsthan in old leaves. Old leaves were capable of maintaining openstomata at lower leaf water potentials. Opened flowers and newflush leaves lost more water, on a dry weight basis, than flowerbuds, fruit or mature leaves. The results illustrate differencesin leaf water potential and stomatal conductance which can beattributed to the maintenance of leaf turgor by decreases inleaf osmotic potentials as leaves mature. These changes in citrusleaf water relations are especially important since water stressresulting from high water loss rates of new tissues could reduceflowering and fruit set. Citrus sinensis (L.) Osbeck, orange, Citrus paradisi Macf., grapefruit, growth rate, leaf water relations, osmotic potential, water potential, stomatal conductance     

Effect of Drought on Metabolism and Partitioning of Carbon in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the partitioning of carbonon the third and seventh day from anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. The 9-d drought treatment, imposed just after anthesisduring the period of cell division in the grains, reduced grainyield by 18 per cent in Warigal and 30 per cent in Condor. Netcarbon fixation was up to 60 per cent higher in Warigal thanCondor towards the end of the drought period and this correlatedwith better osmotic adjustment in the flag leaf. Carbon partitioningbetween plant organs responded to water deficit more rapidlythan net carbon fixation. On day 3, carbon allocation to theroots of droughted plants was maintained in Condor and increasedby 14 per cent in Warigal, whereas carbon allocation to theear decreased in both varieties. However the roots did not competewell with the ear when the water deficit became more severe.Warigal accumulated 3 times more stem reserves than Condor underdrought. In the roots, the pattern of carbon allocation betweenrespiration and carbon accumulation changed soon after impositionof drought. Although total root respiration decreased underdrought it became more energy efficient, particularly for Warigal,as less respiration took place via the alternative pathway.On day 3, the larger carbon allocation to the roots and thelower root respiration accounted for the 4-times larger sugaraccumulation in droughted roots of Warigal compared with thoseof Condor. Osmotic adjustment in mature leaves and roots maybe of importance for the maintenance of vital processes andfor recovery after drought. Triticum aestivum L., wheat, drought, carbon, partitioning     

The role of organic and inorganic solutes in the osmotic adjustment of drought-stressed Jatropha curcas plants

This study aimed to assess the accumulation of organic and inorganic solutes and their relative contribution to osmotic adjustment in roots and leaves of Jatropha curcas subjected to different water deficit intensity. Plants were grown in vermiculite 50% (control), 40%, 30%, 20% and 10% expressed in gravimetric water content. The water potential, osmotic potential and turgor potential of leaves decreased progressively in parallel to CO₂ photosynthetic assimilation, transpiration and stomatal conductance, as the water deficit increased. However, the relative water content, succulence and water content in the leaves did not show differences between the control and stressed plants, indicating osmotic adjustment associated with an efficient mechanisms to prevent water loss by transpiration through stomatal closure. The K⁺ ions had greater quantitative participation in the osmotic adjustment in both leaves and roots followed by Na⁺ and Cl⁻, while the NO₃⁻ ion only showed minor involvement. Of the organic solutes studied, the total soluble sugars showed the highest relative contribution to the osmotic adjustment in both organs and its concentration positively increased with more severe water deficit. The free amino acids and glycinebetaine also effectively contributed to the osmotic potential reduction of both the root and leaves. The role of proline was quantitatively insignificant in terms of osmotic adjustment, in both the control and stressed roots and leaves. Our data reveal that roots and leaves of J. curcas young plants display osmotic adjustment in response to drought stress linked with mechanisms to prevent water loss by transpiration by means of the participation of inorganic and organic solutes and stomatal closure. Of all the solutes studied, soluble sugars uniquely display a prominent drought-induced synthesis and/or accumulation in both roots and leaves.     

Cell Membrane Stability and Leaf Water Relations as Affected by Potassium Nutrition of Water-Stressed Maize

A field experiment was conducted to investigate the effect ofK nutrition under water stress conditions on cell membrane stabilitymeasured by the polyethylene glycol test, plant growth, internalplant water relations and solute and mineral concentrationsin maize (Zea mays L.). Water-stressed plants showed greateradaptation to water deficits at higher K levels. Cell membranestability increased, leaf water potential and osmotic potentialdecreased, turgor potential increased and stomatal resistancedecreased with increasing K nutrition. Osmotic adjustment wasevident and it may have been influenced by increased K⁺ concentrationsin leaf tissues with increasing K nutrition. Higher leaf thicknessand higher leaf water content were observed at higher K levels.Results suggested that higher supplies of K nutrition may increaseplant production during periods of water stress. Key words: Zea mays L., cell membrane stability, leaf water potential, osmotic adjustment, osmotic potential, potassium nutrition, water stress     

Contribution of osmotic adjustment to the dehydration tolerance of water-stressed pigeon pea (Cajanus cajan (L.) millsp.) leaves

Abstract Water-stressed pigeonpea leaves have high levels of osmotic adjustment at low leaf water potentials. The possible contribution of this adjustment of dehydration tolerance of leaves was examined in plants grown in a controlled environment. Osmotic adjustment was varied by withholding water from plants growing in differing amounts of soil, which resulted in different rates of decline of leaf water potential. The level of osmotic adjustment was inversely related to leaf water potential in all treatments. In addition, at any particular water potential, plants that had experienced a rapid development of stress exhibited less osmotic adjustment than plants that experienced a slower development of stress. Leaves with different levels of osmotic adjustment died at water potentials between –3.4 and –6.3 MPa, but all leaves died at a similar relative water content (32%). Consequently, leaves died when relative water content reached a lethal value, rather than when a lethal leaf water potential was reached. Osmotic adjustment delayed the time and lowered the leaf water potential when the lethal relative water content occurred, because it helped maintain higher relative water contents at low leaf water potentials. The consequences of osmotic adjustment for leaf survival in water-stressed pigeonpea are discussed.