Water stress effects on maize: Carbohydrate metabolism of resistant and susceptible cultivars ofZea mays L.

Carbohydrate changea in drought resistant and susceptible cultivars ofZea mays L. were studied at two different stages under imposed water stress in water culture experiments. The gradual decline in total carbohydrates with increasing stress levels was observed. At the 1st leaf stage starch content of the resistant cv. Agati-76 was lower than that of susceptible cv. Vijay but the reducing and non-reducing sugar content was much higher. At the 3rd leaf stage starch content was similar in two cultivars but sugar content was higher in the resistant cv. Agati-76. Differential changes in root and shoot carbohydrates as affected by increasing levels of stress were noticed. Carbohydrate changes have been discussed in relation to drought resistance.     

Effect of water stress on protein content in two maize cultivars differing in drought resistance

The changing pattern, of WSD and concomitant protein changes were scanned in twoZea mays cultivars, with differential sensitivity to water stress. Increasing protein values were recorded in resistant cv. Ageti-76 with decreasing osmotic potentials of substrate (on 3rd day of stress), although the values in susceptible cv. Vijay remained almost on a par with the controls. In another experiment both the cultivars revealed initial increase of protein on 2nd day at osmotic potentials of - 2 and -4 × 10⁶ Pa, however, values declined up to day 7 of stress. WSD showed an increasing trend in both the experiments, although slightly higher values of WSD were registered in cv. Ageti-76 in comparison with cv. Vijay. The significance of protein changes in reference to drought is discussed.     

Response of antioxidant and osmoprotective systems of wheat seedlings to drought and rehydration

Complex study of the effect of soil drought (72 h) and subsequent rehydration for 24 and 48 h on the activities of antioxidant and osmoprotective systems in the leaves of young plants of winter wheat (Triticum aestivum L.) cvs. Ballada (high productivity) and Beltskaya (low productivity) was carried out. Under drought conditions, the content of water in the leaves of cv. Ballada reduced to a lesser degree than in the leaves of cv. Beltskaya. Drought did not affect the rate of leaf growth in cv. Ballada but retarded leaf growth in cv. Beltskaya. Under drought conditions, the content of ascorbate reduced in cv. Beltskaya but was not changed in cv. Ballada; the content of glutathione increased by 19% in cv. Ballada and by 30% in cv. Beltskaya. Under drought conditions, ascorbate peroxidase activity was not changed in cv. Ballada whereas in cv. Beltskaya there was a tendency to its decrease. Glutathione reductase activity in the leaves of cv. Beltskaya increased stronger than in cv. Ballada. Substantial differences between cultivars in the accumulation of reducing sugars and sucrose under water deficit were observed. In both cultivars, drought induced an active proline accumulation. Observed differences in the cultivar responses to water stress evidently indicate differences in the strategy of their adaptation to drought. Drought did not affect the contents of chlorophyll and MDA in both cultivars. The data obtained allow a suggestion that, under conditions of moderate soil drought, the coordinated system of antioxidant defense and osmotic control functioned sufficiently effective; as a result, oxidative stress was not developed in both cultivars. Young plants of both cultivars differing in their responses to water deficit retained the ability to recover after rehydration.     

Response of pigeon pea cultivars to water stress

Decrease in soil water potential during vegetative and flowering stages of two cultivars of pipeon pea (Cajanus cajari) caused higher decrease in relative water content in cv. ICPL-151 than in cv. H-77-216. Both cultivars showed partial recovery during rehydration. Cv. H-77-216 also accumulated more proline and carbohydrates during stress and showed better drought tolerance than cv. ICPL-151.     

Water deficit enhancement of proline and α-amino nitrogen accumulation in potato plants and its association with susceptibility to drought

Potato plants ( Solanum tuberosum L. cvs 'Up-to-Date', 'Desiree', 'Alpha', 'Spunta', 'Elvira' and 'Troubadour') were exposed to cycles of water stress and relief during growth. Severe water deficit induced increased proline content 6- to 7-fold in nonturgid leaves which just started to wilt, and 8- to 27-fold in fully wilted leaves of potatoes. However, proline content was not affected during the early stages of stress development over a range of osmotic potentials in the leaves. The rising proline content was related to turgor loss of leaves independent of changes in the osmotic potentials, which indicates that proline involvement in osmoregulation of potato leaves is unlikely.
Repeated cycles of water stress and relief resulted in increased proline and α-amino nitrogen content in the tuber tissue of some of the cultivars. The smallest increase in proline content was obtained in 'Alpha' tubers and the content of α-amino nitrogen remained unaffected by the water stress. Concomitantly, 'Alpha' was the most drought-tolerant cultivar, as determined by its capacity to accumulate dry matter in tubers under stress conditions. On the other hand, in tubers of cultivars which were more susceptible to drought, a marked increase in proline and α-amino nitrogen was observed in response to water stress. The possible association of these findings with tolerance of potatoes to repeated short periods of drought is discussed.     

Antioxidant defense system,lipid peroxidation,proline-metabolizing enzymes,and biochemical activities in two <Emphasis Type="Italic">Morus alba</Emphasis> genotypes subjected to NaCl stress

Salt stress-induced changes in antioxidant enzymes, lipid peroxidation, proline and glycine betaine contents, and proline-metabolizing enzymes were examined in the leaves of two mulberry cultivars (Local and Sujanpuri). With increasing salinity up to 150 mM NaCl, superoxide dismutase, catalase, ascor-bate peroxidase, guaiacol peroxidase, glutathione reductase, and monodehydroascorbate reductase activities were increased in both cultivars as compared to control, but more pronounced increase was observed in cv. Local. Salt stress enhanced the rate of lipid peroxidation (as indicated by increasing MDA content) in both cultivars. Under NaCl stress, cv. Local showed less change in the MDA content than cv. Sujanpuri. Salt stress resulted in a significant accumulation of free proline in mulberry leaves, and more accumulation was detected in cv. Local than cv. Sujanpuri. The leaves of cv. Local showed 9-fold accumulation of glycine betaine in comparision with cv. Sujanpuri after 20 days at 150 mM NaCl. A decrease in proline oxidase activity and an increase in γ-glutamyl kinase activity were observed with increasing NaClconcentration. The relative water content and electrolyte leakage also decreased after increasing the NaCl concentration, but a decrease was more pronounced in cv. Sujanpuri than in cv. Local. The results indicate that oxidative stress may play an important role in salt-stressed mulberry plants and cv. Local have more efficient antioxidant characteristics, which could provide for a better protection against oxidative stress.     

Effect of water stress on growth and proline metabolism of Phaseolus vulgaris L.

Summary The effect of water stress on growth (fresh weight, dry weight), water relations (water saturation deficit, water potential, osmotic pressure), and proline metabolism in Phaseolus vulgaris were studied.Experimentally, water deficit was produced by reduced watering of the bean plants. This resulted in a decrease in water potential and leaf fresh and dry weight. Increases in the water saturation deficit and the osmotic pressure of the sap were, however, recorded. Water stress was also induced by treatment of the plants with polyethylene glycol, but its effects on the above mentioned parameters were different. In addition, necrosis of the foliage was observed. According to the present results, polyethylene glycol seems to be suitable only for the induction of short-termed water stress conditions.The effects of water stress on growth and on water relations of the plants were accompanied by a marked increase in the free amino acid content, especially that of the free proline content of the plants. The activities of the proline dehydrogenase and glutamate dehydrogenase were stimulated under water stress conditions, indicating that proline accumulation in water stressed plants is not attributed to an inhibited proline breakdown. The accumulated proline was metabolized rapidly once the water deficit of the plant was relieved by watering. The ability of the plant to accumulate proline might be of ecological importance for the plant and might be an adaption mechanism of the plant to overcome short periods of drought.Abbreviations -Kg -ketoglutarate - GDH glutamate dehydrogenase - PDH proline dehydrogenase - P5C -pyrroline-5-carboxylic acid - PEG polyethylene glycol - WSD water saturation deficit     

Leaf recovery responses during rehydration after water deficit in two bean (Phaseolus vulgaris L.) cultivars

Abstract

Our hypothesis was that recovery responses (RI and RII) upon rehydration, after 1 and 8 d of moderate (WDI) and severe water deficit (WDII), are evidence of tolerance in two commercial bean cultivars, Tacarigua (T cv) and VUL-73-40 (V cv). Recovery of leaf water (Ψw) and osmotic potentials (Ψs), and relative water content (LRWC), showed strong dependence on soil water potential (sΨw) followed by protein content; recovery connection between stomatal conductance and soil Ψw is showed. Chlorophyll (a + b), Ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) activity, dry biomass (DM), and leaf area (LA) recovery were sensitive to WD intensity. Specific leaf area (SLA) and leaf density (D) recovery were less dependent on WD intensity and in time-dependent manner; V cv recovery was slower, showed faster recovery of Rubisco activity and DM due to slower recovery in SLA and D, which promoted it. Rubisco activity presented correlations with LRWC and Ψw at moderate and severe WD in both cultivars, and significant correlation with Ψs was observed in V cv. We conclude that recovery after rehydration reveals intrinsic tolerance to WD, due to an integration of metabolic and structural interactions, in responses to leaf water status components.     

Photosynthetic, Physiological and Biochemical Responses of Tomato Plants to Polyethylene Glycol-Induced Water Deficit

Polyethylene glycol （PEG 6000）-induced water deficit causes physiological as well as biochemical changes in plants. The present study reports on the results of such changes in hydroponically grown tomato plants （Lycopersicon esculentum Mill. cv. Nikita）. Plants were subjected to moderate and severe levels of water stress （i.e. water potentials in the nutrient solution of- 0.51 and -1.22 MPa, respectively）. Water stress markedly affected the parameters of gas exchange. Net photosynthetic rate （Pn） decreased with the induction of water stress. Accordingly, a decrease in the transpiration rate （E） was observed. The ratio of both （Pn/E） resulted in a decrease in water use efficiency. One of the possible reasons for the reduction in Pn is structural damage to the thylakoids, which affects the photosynthetic transport of electrons. This was indicated by an increase in non-photochemical quenching and a reduction in the quantum yield of photosystem Ⅱ. Furthermore, a decrease in both leaf water potential and leaf osmotic potential was observed, which resulted in a significant osmotic adjustment during stress conditions. Analysis of the physiological responses was complemented with a study on changes in proline content. In stressed plants, a 10-fold increase in proline content was detected compared with control plants. It is clear that water stress tolerance is the result of a cumulative action of various physiological and biochemical processes, all of which were affected by PEG 6000-induced water stress.     

Effect of drought on chlorophyll content and antioxidant enzyme activities in leaves of three wheat cultivars varying in productivity

Seedlings of three wheat varieties (Triticum aestivum L.)—highly productive cv. Ballada, moderately productive cv. Belchanka, and low productive cv. Beltskaya—were exposed to progressive soil drought (cessation of watering for 3, 5, and 7 days) and then analyzed for chlorophyll content and activities of ferredoxin-NADP⁺ oxidoreductase (FNR) and antioxidant enzymes, namely, glutathione reductase (GR) and ascorbate peroxidase (AscP). In addition, the proline content, and the extent of lipid peroxidation were examined. In the first period of water limitation, the water loss from leaves was slight for all wheat cultivars, which is characteristic of drought-resistant varieties. After 7-day drought the leaf water content decreased by 5.2–6.8%. The total chlorophyll content expressed per unit dry weight increased insignificantly during the first two periods of drought but decreased by 13–15% later on. This decrease was not accompanied by changes in chlorophyll a/b ratio. The plant dehydration did not induce significant changes in FNR activity. Activities of GR and AscP in leaves of wheat cultivars Ballada and Belchanka increased on the 3rd and 5th days of drought. Owing to the coordinated increase in GR and AscP activities, the lipid peroxidation rate remained at nearly the control level observed in water-sufficient plants. When the dehydration period was prolonged to 7 days, activities of GR and AscP in wheat cultivars reduced in parallel with the increase in malonic dialdehyde (MDA) content, indicating that the antioxidant enzyme defense system was weakened and lipid peroxidation enhanced. Unlike Ballada and Belchanka, the wheat cv. Beltskaya did not exhibit the increase in GR and AscP activities during progressive soil drought. The increase in MDA content by 16% in this cultivar was only observed after a 7-day drought period. The proline content in leaves of all wheat cultivars increased substantially during drought treatment. Thus, in wheat cultivars examined, different responses of the defense systems were mobilized to implement plant protection against water stress. The activities of antioxidant enzyme defense system depended on wheat cultivar, duration of drought, and the stage of leaf development.     

Comparison of the physiological responses of Phaseolus vulgaris and Vigna unguiculata cultivars when submitted to drought conditions

Three cultivars differing in their susceptibility to water stress were compared—Phaseolus vulgaris cv. Carioca (susceptible), Vigna unguiculata cv. IT83D (intermediately tolerant) and V. unguiculata cv. EPACE-1 (tolerant)—during an imposed water stress treatment. Variation in leaf gas exchange (i.e. assimilation and stomatal conductance) and leaf relative water content in response to progressive substrate water depletion were investigated. To verify the extent of the injury caused by the drought treatment, leaf gas exchange was measured after rehydration. In the three cultivars, stomatal conductance declined before leaf relative water content was affected. P. vulgaris showed the largest decrease in the rate of stomatal conductance with decreasing substrate water content compared to both V. unguiculata cultivars. Photosynthetic assimilation rates were largely dependent on stomatal aperture, but there was evidence of the participation of non-stomatal factors in the reduction of CO₂ fixation. The response of leaf gas exchange parameters to severe water stress conditions differed significantly between P. vulgaris and V. unguiculata cultivars. After rehydration, cultivars can be characterised according to the degree of injury induced by the drought treatment: V. unguiculata cv. EPACE-1 as the least affected, V. unguiculata cv. IT83D slightly affected and P. vulgaris cv. Carioca strongly affected. Similar ranking was obtained with experiments previously performed at a cellular and subcellular level. Our results confirm the utility of physiological parameters as early screening tools for drought resistance in bean cultivars.     

干旱和复水对草莓叶片叶绿素荧光特性的影响

采用日本丰香草莓(Fragaria×ananassa Duch.cv.Toyonoka)品种进行实验,研究干旱和复水对其叶片叶绿素荧光特性的影响。结果表明,随着干旱胁迫程度的加剧,草莓叶片的最大荧光(Fm)、PSⅡ原初光能转化效率(Fv/Fm)、PSⅡ实际光化学效率(Yield)、光化学猝灭系数(qP)都随干旱胁迫的加剧而下降。干旱胁迫14d后,不同处理组草莓叶片的叶绿素荧光参数存在着显著的差异(P0.05)。复水后,低度胁迫和中度胁迫处理组能较快地恢复到正常水平,但重度胁迫组与对照组存在着显著的差异(P0.05)。     

Photosynthetic responses and proline content of mature and young leaves of sunflower plants under water deficit

In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO₂ concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the F_v/F_m in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants.     

Free proline accumulation in drought-stressed plants

Summary Free-proline accumulation was measured in leaves of intact wheat (Triticum vulgare L. cv. Kalyan Sona), plantago (Plantago ovata Forsk-Isabgool), papavar (Papaver somnifera L. Opium poppy) and mustard (Brassica juncea L. var. Varuna) grown in the field with low to high field water content and thus they were subjected to water stress. Leaf water deficit in percentage was used to determine the degree of stress at the time of proline anlysis.Free proline content was higher in mustard leaves as compared to wheat, plantago and papavar leaves. Water stress enhances the proline content but at same water deficit level the content differ in the leaves of the plants studied.     

Arbuscular mycorrhiza improved growth performance in Macadamia tetraphylla L. grown under water deficit stress involves soluble sugar and proline accumulation

Water deficit limits plant growth and yield. Arbuscular mycorrhizal (AM) symbiosis is viewed as one of the several methods to improve growth under water deficit. The present study investigated the growth performance in relation to water deficit in two cultivars (“H2” and “660”) of AM treated macadamia (Macadamia tetraphylla L.) plants. AM treatment significantly improved the growth in macadamia plants that have been subjected to water deficit (7 % soil water content) for 14 days. Leaf water content (LWC) and maximum quantum yield of PSII (F_v/F_m) in AM-associated plants were maintained better than those in the control (well-watered) plants. A positive correlation was observed between LWC and F_v/F_m in “H2” cultivar. AM treatment enhanced proline and soluble sugar content in “H2” cultivar under water deficit stress. In contrast, only soluble sugars were accumulated in the AM-associated plants of “660” cultivar under water deficit stress. The study concludes that soluble sugars and proline are involved as key signals of osmoregulation defense response, improve water relation in plant tissues, and thereby resulting in improved growth in AM-associated macadamia plants.     

Photosynthetic CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>O gas exchange and dynamics of carbohydrates content in maize leaves under drought

We studied the temporal sequence of changes in the photosynthetic CO₂/H₂O gas exchange intensity, as well as leaf water status, contents of soluble carbohydrates, starch, proline, pigments, and MDA, in maize seedlings (Zea mays L., cv. Luchistaya) under adaptation to increasing water deficit. The duration of drought was 2, 3, 5, and 6 days. Withholding water from maize plants caused gradual increase in the intensity of water deficit: from mild (2 or 3 days) to moderate (5 days) and nearly severe (6 days) water stress. After 6 days, relative leaf water content decreased by 19.8% as compared to the control. On the second day after the onset of drought, slight reduction in the photosynthetic CO₂/H₂O gas exchange intensity of the treated plants was observed. After 6 days, photosynthesis and transpiration of leaves synchronously reduced almost threefold due to stomatal closure. The progressive soil drought had substantial impact on the carbohydrate metabolism. After 2 days of water deficit, the content of reducing sugars and sucrose increased slightly, whereas after 6 days, it increased ten and four times, respectively. After 2, 3, and 5 days of drought, the starch content declined slightly; however, under severe drought (6 days), it increased by 30% as compared to the control. Simultaneously with the increase in the content of soluble sugars, proline content increased significantly and it was the highest on the sixth day of drought. At all stages of water deficit, the proline content increased more significantly than the content of reducing carbohydrates and sucrose. Under increasing water deficit (5 and 6 days), the content of MDA was found to rise. At the initial drought stage (2 or 3 days) and under severe water deficit (6 days), no significant changes in the pigment content were observed. Thus, at the initial stages of progressive drought, in the leaves of this maize cultivar, a decline in photosynthetic activity proceeded simultaneously with accumulation of reducing sugars, sucrose, and proline. The results obtained showed that, at the first stages of adaptation of maize seedlings to drought, the changes in carbohydrate and proline metabolism have been observed, which have increased upon further plant dehydration.     

Response of French bean cultivars to water deficits: Changes in endogenous hormones, proline and chlorophyll

Effects of water stress at different stages of plant growth on leaf relative water content (RWC), osmotic potential (Ψos) and changes in contents of chlorophyll, abscisic acid (ABA), zeatin riboside (t-ZR), ethylene and proline in six cultivars of French bean (Phaseolus vulgaris L.) were studied. Under water stress, Ψos and RWC were highest in cv. Contender and lowest in cvs. IIHR-909 and Sel-2. The increase in contents of ABA and proline was marked in cv. Contender followed by cv. UPF-626. Decrease in t-ZR and chlorophyll contents was prominent in cv. IIHR-909. Ethylene production surged in all the cultivars under 4- and 8-d stress and declined under 12-d stress. This revised version was published online in August 2006 with corrections to the Cover Date.     

Time-Course Studies on Accumulation of Hydrophilic Antioxidants to Different Stress Regimes Followed by Recovery in Contrasting Cultivars of Wheat

Under unpredictable climatic scenarios, drought is one of the major environmental constraints limiting plant growth and productivity in arid and semi-arid regions. Rapid recovery from drought is of paramount importance for the persistence and survival of different crops growing worldwide. The boiling soluble proteins, BSPs (proteins remaining soluble upon boiling in aqueous solution) forms an instrumental part of the response to water deficit conditions and might be of key importance for the survival of plants under unfavourable environmental conditions. These BSPs are typified by two unique properties: high hydrophilicity and high thermal stability. The main objective of the study was to determine drought-induced changes in the markers of oxidative stress along with modulation in the activity of the boiling soluble antioxidants in response to different stress regimes followed by re-watering in Triticum aestivum L. In this study, we determined the indices of oxidative stress (membrane injury index (MII) and lipid peroxidation in terms of malondialdehyde (MDA) content) and activities of boiling soluble antioxidant enzymes in seeds of sensitive and tolerant cultivars of wheat at different duration of stress (3, 6 and 10 days) followed by recovery (post stress harvest). Water content recorded a decline in the sensitive (PBW 343 and PBW 621) as well as tolerant (PBW 527 and PBW 175) cultivars in stress duration and cultivar dependent manner and this was reversed following re-watering in all the cultivars. Oxidative stress indicators also increased in all the cultivars at different stress intensities but this was reversed following re-watering in the tolerant cvs. PBW 175 and PBW 527. At 3 and 6 days, boiling soluble monodehydroascorbate reductase (BsMDAR), boiling soluble protein disulphide isomerase (BsPDI) activity increased in both the tolerant cvs. PBW 175 and PBW 527 whereas boiling soluble guaiacol peroxidase (BsGPX) increased in the sensitive cv. PBW 343. However, as the stress intensity increased to 10 days, BsMDAR, boiling soluble glutathione-S-transferase (BsGST) and BsGPX increased only in the tolerant cvs. PBW 175 and PBW 527, thus accentuating their cardinal roles in stress tolerance under harsh drought conditions. Upon re-watering the stress plants after 10 days, BsMDAR increased only in the tolerant cv. PBW 175. On the other hand, boiling soluble protein disulphide isomerase (BsPDI) increased in both the tolerant cv. PBW 175 and susceptible cv. PBW 343, but with a greater enhancement in the cv. PBW 175. Based upon our results, biochemical significance of the boiling soluble antioxidants in the cultivars of wheat differing in drought resistance during different stress intensities and recovery is discussed.     

Water relations and nitrogen fixation in potassium fedVigna radiata nodules

Drought created by withholding the irrigation at 30 and 45 d after sowing significantly decreased relative water content (RWC) and osmotic potential (ψ_s) ofVigna radiata (L.) Wilczek cv. MH-83-30 nodules. Potassium fed plants showed higher RWC, whereas ψ_s was further declined irrespective of soil moisture levels. The nitrogenase activity and leghemoglobin content of nodules markedly decreased under drought and nodules of potassium fed plants showed better recovery after rehydration. The proline content significantly increased under drought but declined upon reirrigation. Also, the C, N and K contents of nodules significantly declined under drought.     

Hexaconazole induces antioxidant protection and apigenin-7-glucoside accumulation in Matricaria chamomilla plants subjected to drought stress

In this experiment, the possibility of enhancing the water deficit stress tolerance of chamomile (Matricaria chamomilla L.) during two growth stages by the exogenous application of hexaconazole (HEX) was investigated. To improve water deficit tolerance, HEX was applied in three concentrations during two different stages (50 and 80 days after sowing). After HEX applications, the plants were subjected to water deficit stress. Although all HEX concentrations improved the water deficit stress tolerance in chamomile plants, the application of 15 mg L⁻¹ provided better protection when compared to the other concentration. The exogenous application of HEX provided significant protection against water deficit stress compared to non-HEX-treated plants, significantly affecting the morphological characteristics and aspects of productivity, the relative water, protein and proline contents; non-enzymatic and enzymatic antioxidants; and the flower's apigenin-7-glucoside content. These results suggest that the HEX-induced tolerance to water deficit stress in chamomile was related to the changes in growth variables, antioxidants and the apigenin-7-glucoside content.