Negative Effects Of Water Stress Research Articles

Physiological Integration Ameliorates Negative Effects of Water Stress in Salt-sensitive ‘C198’ Common Bermudagrass

Clonal plants can consist of connected individual ramets that enhance resource sharing through physiological integration. This integration enables the whole clone to tolerate environmental stresses. The objective of this research was to investigate the effects of physical ramet connections on the integration of antioxidant enzymes in clonal common bermudagrass (Cynodon dactylon) growing under heterogeneously distributed water; i.e., nonuniform distribution of water due to 20% polyethylene glycol (PEG 6000) treatment on some ramets and not others. The bottom, middle, upper and three fragments of clonal common bermudagrass were subjected to 20% PEG 6000 with water potential of −1.8 MPa to induce heterogeneous and homogeneous drought stress. The control was not treated with 20% PEG 6000. Within the heterogeneous treatment, water stressed clonal fragments generally had higher leaf and root antioxidant enzyme activities with respect to superoxide dismutase, catalase, peroxidase (except for root peroxidase). There was no difference in antioxidant enzyme activity within the connected clonal ramets for homogeneous treatment; i.e., three connected ramets treated with 20% PEG 6000. Osmotically stressed clonal fragments under heterogeneous environments had a lower level of malonaldehyde (MDA) compared with those in homogeneous regimes. The antioxidant enzyme integration was affected by directionality and water availability contrast. This was indicated by significant decline in MDA levels within the heterogeneous treatments as compared with homogeneous treatment, which suggested reduced lipid peroxidation. These results suggested that ramet connections facilitate integration of antioxidant enzymes within clonal plants growing in heterogeneously available water. Enzymes were integrated from clonal fragments growing in water sufficient environment to those in water stressed regimes. This enhanced reactive oxygen species scavenging capacity of the entire clone hence improved drought tolerance.

Exogenous Salicylic Acid and Trehalose Ameliorate Short Term Drought Stress in Wheat Cultivars by Up-regulating Membrane Characteristics and Antioxidant Defense System

In this study, the protective role of salicylic acid (SA) and trehalose (Tre) in relation to lipid peroxidation, membrane leakage, membrane stability index, antioxidant defense system as well as non-enzymatic antioxidants were investigated in drought stressed wheat Gemmieza-7 (drought sensitive cultivar) and Sahel-1 (drought tolerant cultivar) plants. Water stress reduced bio-membranes stability through inducing its lipid peroxidation resulting in an increment in membrane leakage with marked decrease in membrane stability index of flag leaf of both wheat cultivars during grain-filling. Moreover, it was obvious that drought significantly increased the activity of ascorbic acid oxidase (AAO), peroxidase (POD) and phenylalanine ammonia lyase (PAL) activities and induced non-significant reduction in polyphenol oxidase (PPO) activity in flag leaves of both wheat cultivars during grain-filling in comparing with well watered plants. Among cultivars, tolerant one showed higher enzymes activity than the sensitive one. Application of SA and/or Tre markedly increased AAO, POD and PAL activities and non-significant decrease in PPO activity in flag leaf of water stressed wheat plants. Generally, SA and Tre treatment appeared to be the most effective treatment in counteracting the negative effects of water stress and Sahel-1 appeared to induce better results than Gemmieza-7 and proved to be more tolerant. Drought stress caused significant increase in the amount of total phenols and flavonoids in flag leaf of both cultivars during grain-filling where the sensitive plants accumulated more total phenols and flavonoids contents than the tolerant one. Furthermore, water stress increased the non-photosynthetic pigment content of the two wheat cultivars particularly drought sensitive one during grain filling. These results suggest that the exogenous application of SA and/or Tre assisted the plants to become more tolerant to drought stress-induced oxidative damage by upregulating the membrane characteristics and enhancing their antioxidant defense system as well as non- enzymatic antioxidants.

Deficit Irrigation and Organic Compost Improve Growth and Yield of Quinoa and Pea

AbstractSupplying organic matter under deficit irrigation conditions could be a practical solution to compensate the negative effect of water stress. For this purpose, studies in pea as a legume and quinoa as a new drought‐tolerant crop were conducted in the south of Morocco between October 2011 and March 2012. Three organic matter levels (0, 5 and 10 t ha−1) were supplied as compost amendment combined with 2 irrigation levels (50 and 100% of full irrigation). The results indicate that stomatal conductance and dry matter have been affected significantly (P < 0.05) only by deficit irrigation, while harvested yield was affected significantly (P < 0.05) by both deficit irrigation and organic manure. The highest seed yields (3.3 t ha−1 for quinoa and 5.6 t ha−1 for pea) were recorded under full irrigation and 10 t ha−1 of compost. Results indicated that organic amendment of 10 t ha−1 and 5 t ha−1 significantly (P ≤ 0.05) increased seed yield by 18 and 11% under stress conditions and by 13 and 3% under full irrigation for quinoa and by 24 and 11% under full irrigation and by 41 and 25% under water‐deficit irrigation for pea. It can be concluded that organic amendment improved significantly yield and biomass production better under deficit irrigation conditions than under full irrigation. Combining deficit irrigation and organic amendment led to the maximization of crop water productivity.

Influence of Arbuscular Mycorrhizae on Biomass Production and Nitrogen Fixation of Berseem Clover Plants Subjected to Water Stress

Several studies, performed mainly in pots, have shown that arbuscular mycorrhizal symbiosis can mitigate the negative effects of water stress on plant growth. No information is available about the effects of arbuscular mycorrhizal symbiosis on berseem clover growth and nitrogen (N) fixation under conditions of water shortage. A field experiment was conducted in a hilly area of inner Sicily, Italy, to determine whether symbiosis with AM fungi can mitigate the detrimental effects of drought stress (which in the Mediterranean often occurs during the late period of the growing season) on forage yield and symbiotic N2 fixation of berseem clover. Soil was either left under water stress (i.e., rain-fed conditions) or the crop was well-watered. Mycorrhization treatments consisted of inoculation of berseem clover seeds with arbuscular mycorrhizal spores or suppression of arbuscular mycorrhizal symbiosis by means of fungicide treatments. Nitrogen biological fixation was assessed using the 15N-isotope dilution technique. Arbuscular mycorrhizal symbiosis was able to mitigate the negative effect of water stress on berseem clover grown in a typical semiarid Mediterranean environment. In fact, under water stress conditions, arbuscular mycorrhizal symbiosis resulted in increases in total biomass, N content, and N fixation, whereas no effect of crop mycorrhization was observed in the well-watered treatment.

Respostas fisiológicas de genótipos de Eucalyptus grandis x E. urophylla à disponibilidade hídrica e adubação potássica

Conduziu-se este trabalho, com o objetivo de estudar as respostas fisiológicas de cinco genótipos de eucalipto à disponibilidade hídrica e adubação potássica. As mudas foram plantadas em vasos preenchidos com sete litros de um Neossolo Quartzarênico, com baixo teor natural de potássio (0,2 mmol c.dm-3 K), e submetidas a dois regimes de irrigação (RI1 - diário e RI2 - irrigação suspensa até o aparecimento de sintomas iniciais de murcha), sem (K0) e com suprimento de potássio (K1 - 200 mg.dm-3 K2O), em casa de vegetação. Avaliou-se a taxa fotossintética (A), condutância estomática (gs), transpiração (E), índice de conteúdo de clorofila (ICC), conteúdo relativo de água (CRA), eficiência fotoquímica (Fv/Fm), eficiência intrínseca (EUAintr) e instantânea no uso da água (EUAinst) e potencial hídrico foliar (Ψf). O experimento foi estabelecido no delineamento de blocos ao acaso, em esquema fatorial 5 x 2 x 2 (5 genótipos, 2 regimes de irrigação e 2 níveis de adubação potássica), com cinco repetições. À exceção da eficiência fotoquímica, as demais características apresentaram alterações significativas no regime RI2, com redução nos valores de A, gs e E e aumento em ICC e EUAinst. O suprimento de potássio nas plantas do RI2 proporcionou maiores valores de A, gs, E e CRA. Dos genótipos avaliados, o G1 é o mais resistente e o G2 o mais sensível à deficiência hídrica. Conclui-se que a adubação potássica pode amenizar os efeitos negativos da deficiência hídrica nos estádios iniciais de crescimento de eucalipto.

Effects of irrigation and fruit position on size, colour, firmness and sugar contents of fruits in a mid-late maturing peach cultivar

Experiments were conducted on a mid-late maturing peach (Prunus persica) cv. ‘Catherine’ in 2008 in order to study the influences of irrigation and fruit location within the canopy, on fruit growth and several fruit-quality attributes, including sugar and acid contents. Trees were subjected to full irrigation (FI) and regulated deficit irrigation (RDI). Fruit height in the crown, exposure to sunlight and orientation were recorded. Fruit diameter, fresh weight, firmness, flesh and skin colour attributes, soluble solids content, pH and sugar and acid contents were determined for each fruit at harvest. Water stress had a high impact on most of the fruit-quality variables studied. Fruits from trees under RDI were firmer than those from FI trees but did not differ in weight and diameter, perhaps due to the low crop load supported by the studied trees. In contrast, fruits from RDI trees had more soluble solids, glucose, sorbitol, and malic, citric and tartaric acids. Height in the crown partially affected positively soluble solids content. Exposure to sunlight strongly influenced stone dry weight and soluble solid content. Finally, orientation did not have a significant influence on most of the fruit-quality attributes considered in this study. Our results suggested that leaving a low crop load on the tree maintaining fruits only in the most ideal parts of the canopy may improve fruit quality under water restriction conditions. In this way, the negative effects of water stress may be counteracted and fruit quality for this mid-late maturing peach cultivar would be improved.

Combined effects of water stress and fruit thinning on fruit and vegetative growth of a very early-maturing peach cultivar: assessment by means of a fruit tree model, QualiTree

Regulated deficit irrigation strategies are common practices in areas with low water availability. Thus, water stress, which can limit fruit growth, is imposed to the trees. Fruit thinning can be used to relieve this water stress in peach. In this paper, the ability of an existing fruit tree model (QualiTree) for describing the effects of water stress and fruit thinning on peach fruit and vegetative growth was assessed. The model was parameterized and calibrated for a very early-maturing peach cultivar (“Flordastar”). Important parameters were those expressing the effect of distance between organs on carbon exchange within the tree, the potential dry masses, and the relative growth rates of fruits and leafy shoots. Then, the model was tested in a wide range of water stress situations and three fruit thinning intensities: no thinning, commercial thinning, and heavy thinning. Fruit and vegetative growth simulations were consistent with observed data derived from 2006 field experiments. The variability over time of fruit and vegetative growth was well predicted. The model reproduced reductions in fruit growth observed in field experiments. It also reacted to simulated scenarios that combined water stress and thinning. Increasing thinning intensity reduced total fruit yield but increased fruit size at harvest, compensating the negative effects of water stress on fruit growth. These simulations broadened the predictive capabilities of the model and showed that it might be a useful tool in the design of innovative horticultural practices.

Effects of elevated CO2 concentration and water deficit on fructan metabolism in Viguiera discolor Baker

Elevated [CO2 ] is suggested to mitigate the negative effects of water stress in plants; however responses vary among species. Fructans are recognised as protective compounds against drought and other stresses, as well as having a role as reserve carbohydrates. We analysed the combined effects of elevated [CO2 ] and water deficit on fructan metabolism in the Cerrado species Viguiera discolor Baker. Plants were cultivated for 18 days in open-top chambers (OTC) under ambient (∼380 ppm), and high (∼760 ppm) [CO2 ]. In each OTC, plants were submitted to three treatments: (i) daily watering (control), (ii) withholding water (WS) for 18 days and (iii) re-watering (RW) on day 11. Analyses were performed at time 0 and days 5, 8, 11, 15 and 18. High [CO2 ] increased photosynthesis in control plants and increased water use efficiency in WS plants. The decline in soil water content was more distinct in WS 760 (WS under 760 ppm), although the leaf and tuberous root water status was similar to WS 380 plants (WS under 380 ppm). Regarding fructan active enzymes, 1-SST activity decreased in WS plants in both CO2 concentrations, a result consistent with the decline in photosynthesis and, consequently, in substrate availability. Under WS and both [CO2 ] treatments, 1-FFT and 1-FEH seemed to act in combination to generate osmotically active compounds and thus overcome water deficit. The proportion of hexoses to sucrose, 1-kestose and nystose (SKN) was higher in WS plants. In WS 760, this increase was higher than in WS 380, and was not accompanied by decreases in SKN at the beginning of the treatment, as observed in WS 380 plants. These results suggest that the higher [CO2 ] in the atmosphere contributed to maintain, for a longer period, the pool of hexoses and of low DP fructans, favouring the maintenance of the water status and plant survival under drought.

Combined effects of irrigation, crop load and fruit position on size, color and firmness of fruits in an extra-early cultivar of peach

Experiments were conducted on a very early-maturing peach (Prunus persica) cv. ‘Flordastar’ in 2006 in order to study the influences of irrigation, fruit load and fruit location within the leafy shoot and the canopy on fruit growth and several fruit-quality attributes. Trees were subjected to full irrigation (FI) and regulated deficit irrigation (RDI, consisting in 25% of FI during stages I and II of fruit development) under two crop loads: commercial and low (half of the commercial crop load). Fruit position on the shoot, height in the crown, their exposure to sunlight and orientation were recorded. Fruit diameter, fresh weight, firmness, and flesh and skin color attributes were determined for each fruit. Water stress and crop load had a high impact on all the variables studied. Fruits from trees under RDI were smaller, lighter and had a higher firmness than those from FI trees. Thinning was not able to counteract the negative effects of water stress on peach fruit size. Exposure to sunlight strongly influenced fruit size, weight, and skin color. Fruits highly exposed to sunlight in water stressed trees were larger. Therefore, leaving a certain fruit distribution on the tree, with fruits more exposed to sunlight, may compensate for the negative effects of water stress on fruit size. Further research is needed on peach-fruit distribution under water restriction conditions.

EFFECT OF POTASSIUM FERTILIZATION ON GROWTH, YIELD AND WATER USE EFFICIENCY OF IRRIGATED POTATO

Studies on the effect of K fertilizers application in increasing water use efficiency (WUE) and decreasing the negative effect of water stress, are quite limited, especially under field conditions. A field experiment was conducted in silty clay loam in the Agricultural Research Station of Abu-Graib- Baghdad, Iraq to study the effect of different levels of K fertilizers application on potato (Solanum tuberosumL.( and their role in decreasing negative effect of water stress. Treatments include four levels of K fertilizer (0, 200, 400 and 600 kg K2SO4 ha -1) and two levels of irrigation (after depletion of 50 and 75 % of available water). Results revealed the following:- The negative effects of water stress on potato growth and yield decreased by increased application of K fertilizers. Negative effects of water stress on plant quality and WUE were decreased by increasing level of K fertilizer in depletion 75% of available water, and saving in irrigation water with irrigation scheduling by 9%. 3. Tuber yield, plant height, leaf area and carbohydrates increased with increased K application. Higher K rates improved yield reached to 30.26 and 25.66 t.ha-1 in irrigation with 50 and 75% depletion of available water, respectively. 4. As a conclusion, nutrients application may have a good impact on plant performance under water stress, and decreasing amount of water applied through alterative irrigation improved yield of fruit. Therefore, this experiment signifies the importance of potassium application together with conserving in water application.

Impact of regulated deficit irrigation on the physiological characteristics of two rapeseed varieties as affected by different potassium rates

A field trial was conducted at experimental field of Qazvin region, Iran (36° 18´ N and 49° 57´ E) in 2008/2009 and 2009/2010 growing seasons to determine the physiological properties of rapeseed varieties (Zarfam and Opera) subjected to drought stress condition under different potassium sulphate levels. The trial was laid out in a factorial experiment based on a randomized complete block design with three replications. Irrigation regimes included I 1 , irrigation after 40% (control); I 2 , irrigation after 60% and I 3 , irrigation after 80% soil water depletion (SWD). However, the applied potassium rates were K 1 , non-application, K 2 , 100 kg ha -1 and K 3 , 200 kg ha -1 of K 2 SO 4 . Physiological indices including relative water content (RWC), stomatal resistance (RS), canopy temperature (T c ), and the difference between canopy and air temperature (ΔT) were measured at three stages. Both varieties regarding physiological indices in all sampling stages showed a significant difference. Higher relative water content (RWC) and lower stomatal resistance (RS) and canopy temperature (T c ) in Opera variety under limited moisture condition indicated its salient drought tolerant over Zarfam variety. Results show that with increasing stress severity in all growing stages, the decrease in RWC and increase in RS and T c was higher when compared with the control which asserts their susceptibility to soil water condition and leaf water potential. Potassium application, in both stressed/non-stressed conditions caused a lower RS and T c , but increased RWC. To sum up, K 2 SO 4 could ameliorate negative effects of water stress on physiological properties and consequently improve them. RWC, RS, T c and ΔT, are beneficial indices for screening large numbers of drought-tolerant rapeseed varieties in a short time at critical stages of crop growth. Key words : Brassica napus L., canopy temperature, potassium fertilizer, relative water content, stomatal resistance, water deficit stress.

Effect of Calcium on Maize Seedling Root Hydraulic Conductivity and Growth under Water Stress and Rehydration Conditions

The effects of extra calcium(additions of 10 mmol L-1 CaCl2 into half-strength Hoagland solution) on maize(Zea mays L.) seedling root hydraulic conductivity(Lpr),morphology and leaf water potential(ψw) were investigated under water stress,which was simulated by 10% PEG-6000 with osmotic potential(ψs) value of -0.2 MPa for seven days,and subsequent two days rehydration.Whole root hydraulic conductivity(Lpr) and leaf water potential(ψw) were determined by pressure chamber.After these treatments,it could be seen that water stress reduced Lpr,which was restored when calcium was added to the solution for growing the water-stressed plants.In addition,the Lpr recovered to the level of the control after re-watering at high Ca2+ level,but the recovery of Lpr was only 59.06% at regular Ca2+ level.HgCl2(50 μmol L-1) treatment caused a sharp decline in Lpr,which was almost restored by treatment with 5 mmol L-1 β-mercaptoethanol.The reduction of Lpr by Hg2+ was 53.20% and 74.55% at regular and high calcium levels,respectively under water stress condition,and 62.1% under normal condition.The results suggest that Ca2+ increased the passage of water through the cell membrane of roots by increasing the activity of Hg-sensitive AQP under water stress.The percentage of reduction by Hg2+ was decreased to the control level two days after re-watering in CaCl2 treated plants.The leaf water potential was declined significantly under water stress,particularly at regular calcium level with respect to the decrease of Lpr.However,ψw recovered rapidly onw day after re-watering.Furthermore,water stress had a detrimental effect on the root growth.The addition of calcium,especially at low water potential,increased the root surface area and primary root diameter,and it promoted primary root enlongation and lateral root development.Compared with the controls,the growth of Ca2+ treated plants was recovered gradually with the prolonging of rehydration.Therefore,these results indicated that the extra calcium,with respect to root growth and water uptake,mitigates the negative effect of water stress and enhances the compensatory effects of rehydration.

Amelioration of water stress by potassium fertilizer in two oilseed species

The effects of potassium fertilizer (K2SO4) levels K0, (0), K1,(150) and K2,(250 kg/ha) in two species of Brassica napus (Hyola 401 Hybrid) and Brassica juncea (landrace cultivar), under three irrigation regimes, control (irrigation after 50%,), moderate stress, (irrigation after 70%), and severe stress (irrigation after 90% soil water depletion) were studied in a factorial experiment laid out in a randomized complete block design with three replications. Grain yield and physiological indices, including relative water content (RWC), stomatal conductance (g), chlorophyll content (SPAD values); leaf temperature (TL), and the difference between canopy temperature and air temperature (Tc-Ta) were measured at two stages (50% flowering and 100% siliques formation. Both species maintained, higher RWC, SPAD values and g, in non stress condition, but decreasing soil water supply caused a lower RWC, SPAD values, g, ∆t and increased TL. Potassium application also improved above mentioned physiological traits. Grain yield was positively associated with RWC, g and SPAD values but showed a negative association with TL and ∆t in both stages. Results showed that with increasing stress severity grain yield reduced significantly, but potassium application conferred great increase on rapeseed yield. Overall, grain yield showed significant association with RWC, g, SPAD values, ∆t and TL under this experiment conditions. It is concluded that potassium application, could ameliorate negative effects of water stress on grain yield and physiological properties and consequently improved them. For selecting drought tolerant cultivars, due to easier measurement of g, SPAD values and TL, they could be recommended for screening large numbers of rapeseed cultivars in a short time at critical stages of crop growth.

Impact of fertilization on drought response in the medicinal herb Bupleurum chinense DC.: Growth and saikosaponin production

Bupleurum chinense DC. is a plant with high medicinal value. Its roots have been used in Chinese medicine for at least 2000 years. Environmental stress has been used as a strategy to optimize yield of important compounds in other crops. The objective of this pot study was to investigate the combined effects of fertilizer and water-stress on total saikosaponin a (SSa) and saikosaponin d (SSd) yield from B. chinense. The 2 × 3 factoral design included two levels of water-stress and three fertilizer amounts. The results showed that mild water-stress significantly increased the SSa and SSd content in B. chinense roots, but decreased root biomass. Total SSa and SSd yield were lower in the water-stressed treatment compared to the well-watered treatment. There was significant interaction between the water and fertilizer treatments and the negative effect of water-stress on total SSa and SSd yield could be partly mitigated through the application of N and P fertilizer. In conclusion, results from this study show that the application of proper amounts of fertilizer are important for medicinal plant production in semi-arid and arid regions, and that it is possible to increase total SSa and SSd yield through the combined use of fertilizer and properly timed exposure to water-stress.

Improving Drought Tolerance by Exogenous Application of Glycinebetaine and Salicylic Acid in Sunflower

AbstractWater shortage is a severe threat to the sustainability of crop production. Exogenous application of glycinebetaine (GB) and salicylic acid (SA) has been found very effective in reducing the adverse affects of drought stress. This study was conducted to examine the possible role of exogenous GB and SA application in improving the yield of hybrid sunflower (Helianthus annuus L.) under different irrigation regimes. There were three levels of irrigation, viz. control (normal irrigations), water stress at vegetative stage (irrigation missing at vegetative stage) and water stress at flowering stage (irrigation missing at flowering stage). GB and SA were applied exogenously at 100 and 0.724 mm, respectively, each at the vegetative and at the flowering stage. Control plants did not receive application of GB and SA. Water stress reduced the head diameter, number of achene, 1000‐achene weight, achene yield and oil yield. Nevertheless, exogenous GB and SA application significantly improved these attributes under water stress. However, drought stress increased the free leaf proline and GB, and were further increased by exogenous application of GB and SA. However, exogenous GB application at the flowering stage was more effective than other treatments. Oil contents were also reduced under water stress; however, GB and SA application could not ameliorate the negative effect of water stress on achene oil contents. The effects of water stress and foliar application of GB were more pronounced when applied at the flowering stage than at the vegetative stage. Moreover, exogenous GB application was only beneficial under stress conditions.

The application of ascorbate or its immediate precursor, galactono-1,4-lactone, does not affect the response of nitrogen-fixing pea nodules to water stress

Nitrogen fixation in legumes is dramatically inhibited by abiotic stresses, and this reduction is often associated with oxidative damage. Although ascorbate (ASC) has been firmly associated with antioxidant defence, recent studies have suggested that the functions of ASC are related primarily to developmental processes. This study examines the hypothesis that ASC is involved in alleviating the oxidative damage to nodules caused by an increase in reactive oxygen species (ROS) under water stress. The hypothesis was tested by supplying 5mM ASC to pea plants (Pisum sativum L.) experiencing moderate water stress (ca. -1 MPa) and monitoring plant responses in relation to those experiencing the same water stress without ASC. A supply of exogenous ASC increased the nodule ASC+dehydroascorbate (DHA) pool compared to water-stressed nodules without ASC, and significantly modulated the response to water stress of the unspecific guaiacol peroxidase (EC 1.11.1.7) in leaves and nodules. However, ASC supply did not produce recovery from water stress in other nodule antioxidant enzymes, nodule carbon and nitrogen enzymes, or nitrogen fixation. The supply of the immediate ASC precursor, galactono-1,4-lactone (GL), increased the nodule ASC+DHA pool, but also failed to prevent the decline of nitrogen fixation and the reduction of carbon flux in nodules. These results suggest that ASC has a limited role in preventing the negative effects of water stress on nodule metabolism and nitrogen fixation.

Influence of water stress and exogenous glycinebetaine on sunflower achene weight and oil percentage

The study was carried out to assess whether exogenously applied glycinebtaine has any role in reducing the adverse effects of water stress on sunflower achene yield and oil contents. Two sunflower lines, Gulshan-98 and Suncross were subjected to water stress at the vegetative and reproductive stages of plant growth. Three levels of glycinebtaine (0, 50 and 100 mM) were applied before sowing (seed treatment) and at the time of initiation of stress at the vegetative and reproductive stages. A marked adverse effect of water stress on 100-achene weight and achene oil contents were observed in both sunflower lines. Exogenous supply of glycinebtaine was not effective in alleviating the adverse effects of water stress on achene oil percentage. Foliar spray of glycinebtaine, however, significantly reduced the negative effects of water stress on achene weight. Seed treatment with either level of glycinebtaine was not effective in increasing the 100-achene weight and achene oil percentage under both normally irrigated and water stress conditions. The sunflower line, Suncross produced higher oil yield than that of Gulshan-98.

Effects of Pre-Treatments with Abscisic Acid and/or Benzyladenine on Gas Exchange of French Bean, Sugar Beet, and Maize Leaves During Water Stress and After Rehydration

Net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) during water stress and after rehydration were measured in Phaseolus vulgaris, Beta vulgaris, and Zea mays. Immediately before imposition of water stress by cessation of watering, plants were irrigated with water (control), 100 μM abscisic acid (ABA), and/or 10 μM N6-benzyladenine (BA). In all three species, application of ABA decreased gs, E, and PN already 1 h after application. However, during water stress gs, E, and PN in plants pre-treated with ABA remained higher than in plants pre-treated with water. Positive effects of ABA application were observed also after rehydration. In contrast, the effects of pre-treatment with BA were species-specific. While in bean plants BA application ameliorated negative effect of water stress, only very slight effects were observed in maize, and in sugar beet BA even aggravated the effects of water stress.

Influence of Phosphorus Application on Water Relations, Biochemical Parameters and Gum Content in Cluster Bean Under Water Deficit

Relative water content (RWC), leaf water potential (Ψw) and osmotic potential (Ψs), contents of chlorophyll (Chl) a, Chl b, soluble sugars, and seed quality (gum content) were used to evaluate the role of phosphorus in alleviation of the deleterious effect of water deficit in clusterbean (Cyamopsis tetragonoloba L. Taub). Under water stress, Ψw, Ψs, and Chl and gum contents decreased and soluble sugar contents increased. Phosphorus application increased Chl and sugar contents in control plants and ameliorated negative effects of water stress.

PLANT WATER STRESS AND ITS CONSEQUENCES FOR HERBIVOROUS INSECTS: A NEW SYNTHESIS

Traditionally, herbivorous insects are thought to exhibit enhanced performance and outbreak dynamics on water-stressed host plants due to induced changes in plant physiology. Recent experimental studies, however, provide mixed support for this historical view. To test the plant-stress hypothesis (PSH), we employed two methods (the traditional vote-counting approach and meta-analysis) to assess published studies that investigated insect responses to experimentally induced water-deficit in plants. For insects, we examined how water deficit affects survivorship, fecundity, density, relative growth rate, and oviposition preference. Responses were analyzed by major feeding guild (sap-feeding insects and chewing insects) and for the subguilds of sap-feeders (phloem, mesophyll, and xylem feeders) and chewing insects (free-living chewers, borers, leaf miners, and gall-formers). Both vote counting and meta-analysis found strong negative effects of water stress on the performance of sap-feeding insects at large and...