Relationship between osmotic stress-induced abscisic acid accumulation,biomass production and plant growth in drought-tolerant and -sensitive wheat cultivars

The effects of increasing osmotic stress induced by 100–400 mOsm (−0.976 MPa) polyethylene glycol (PEG 6000) were investigated in a drought-tolerant (Triticum aestivum L. cv. Mv Emese) and drought-sensitive (cv. GK élet) wheat cultivar at the three-leaf stage. During osmotic stress, the decline of the water potential (ψ _w) was more significant in the leaves, while the abscisic acid (ABA) levels of the roots increased earlier and remained higher in the sensitive than in the tolerant variety. There was an increasing gradient of ABA content toward the youngest leaves in the drought-sensitive GK élet, while more ABA accumulated in the fully developed, older leaves of the tolerant cultivar Mv Emese. In accordance with the rapid and significant accumulation of ABA, the stomatal conductance decreased earlier in the tolerant cultivar. The effect of water stress on the PSII photochemistry was pronounced only 1 week after the exposure to PEG, as indicated by the earlier decrease of the net CO₂ fixation, the effective quantum yield (Φ_PSII) and the photochemical quenching (q _P) in light-adapted samples of the tolerant variety in 400 mOsm PEG 6000. The stress treatment caused more significant reductions in these parameters toward the end of the experiment in the sensitive cultivar. In spite of small differences in the photosynthetic characteristics, the net biomass production was not significantly altered by this osmotic stress. The accumulation of ABA controlled the distribution of the biomass between the shoot and root systems under osmotic stress, and contributed to the development of stronger and deeper roots in the drought-sensitive cultivar GK élet. However, the root elongation did not correlate with the drought sensitivity of these cultivars on the basis of crop yield.     

Drought-induced oxidative damage and antioxidant responses in peanut (<Emphasis Type="Italic">Arachis</Emphasis><Emphasis Type="Italic">hypogaea</Emphasis> L.) seedlings

Two cultivars of peanut (Arachis hypogaea L.) which were designated as resistant (Florispan) and sensitive (Gazipasa) according to their growth retardation under drought stress conditions were compared for their oxidative damage and antioxidant responses. Sixteen days-old peanut seedlings were subjected to PEG-6000 solutions of two different osmotic potentials; −0.4 and −0.8 MPa, and various growth parameters, photosystem II activity, changes in malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and proline levels, activities of ascorbate peroxidase (APX), catalase (CAT), peroxidase (POX) and gluthatione reductase (GR) enzymes were determined. Both cultivars exhibited water deficit at −0.8 MPa osmotic potential of PEG-6000 and H₂O₂ levels significantly increased during exposure to −0.4 MPa osmotic potential. However, H₂O₂ levels were under control in both cultivars at exposure to −0.8 MPa osmotic potential. Significant proline accumulation was observed in the tissues of cv. Florispan at −0.8 MPa osmotic potential, whereas proline accumulation did not appear to be an essential part of the protection mechanism against drought in cv. Gazipasa. No significant variation in chlorophyll fluorescence values were detected in neither of the cultivars. Enzyme activity measurements revealed that Gazipasa copes well with lesser magnitudes of drought stress by increasing the activity of mainly APX, and during harsh stress conditions, only APX maintains its activity in the tissues. In cultivar Florispan, GR activity appears to take role in lesser magnitudes of drought stress, whereas CAT and APX activities appear to be very crucial antioxidative defenses during intense stress conditions. The results indicate that, the level of proline and activities of the enzymes CAT and APX are important mechanisms for the maintenance of drought tolerance in peanut plants.     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

Effect of NaCl and PEG 6000 on germination and seedling growth of rice (ryza sativa L.)

Germination and seedling growth of rice was studied in NaCl and PEG 6000 solutions having osmotic potentials −0.2, −0.4, −0.6 and −0.8 MPa. At isoosmotic concentrations, the NaCl proved more harmful to germination, seedling growth, per cent moisture content of seedling organs as well as mobilization of food matter from seed to the growing seedlings. This fact suggested that in rice, at least in the early stage, a specific ion effect rather than osmotic effect is the prime cause of salt injury. Compared to susceptible cultivar, the tolerant one was less inhibited by salinity.     

Changes in antioxidants and cell damage in heterotrophic maize seedlings differing in drought sensitivity after exposure to short-term osmotic stress

Seedlings of two cultivars of maize (Zea mays L.) differing in their drought sensitivity were exposed to osmotic stress (0.3 M sorbitol, −1.4 MPa) for 4, 8, 12, 24 and 48 h during their heterotrophic stage of development. Alterations in their antioxidant pools combined with the activities of enzymes involved in defence against oxidative stress were investigated. Significant activation of antioxidative defence mechanisms correlated with drought-induced oxidative stress tolerance, and this phenomenon was shown to be characteristic of the drought-tolerant cv. Nova. Activities of some ROS-scavenging enzymes, superoxide dismutase (SOD), guaiacol peroxidase (POX), catalase (CAT) and ascorbate peroxidase (APX) were already enhanced significantly 4 h after the start of drought exposure in the drought-tolerant cv. Nova. Furthermore, a significant increase in the ascorbate pool was observed in this cultivar. On the other hand, in the drought-sensitive cv. Ankora only SOD and POD activities and the thiol pool were increased. No changes in APX activity or the level of ascorbate were recorded in cv. Ankora. Studies of root cell viability indicated that marked oxidative damage appeared only in cv. Ankora. These results, together with our previous observations, confirmed the higher ability of cv. Nova to tolerate drought stress and cope effectively with oxidative damage.     

Differential growth, physiological and biochemical responses of niger (Guizotia abyssinica Cass.) cultivars to water-deficit (drought) stress

The present study demonstrates the effect of polyethylene glycol-8000 (PEG) and percent field capacity (FC%)-induced water-deficit stress on growth, water status, productivity and various biochemical parameters in Guizotia abyssinica Cass. cultivars (IGP 76, GA 10, No. 71 and IGPN 2004) at seedling and maturity stages of the plant. Cultivar GA 10 showed higher, IGP 76 and No. 71 moderate, and IGPN 2004 least reduction in percent seed germination given PEG stress treatments (0, 10 and 20%). A similar pattern was observed for decreased growth and water content of the seedlings and plants of the cultivars exposed to both kinds of water-deficit stresses. The productivity (number of capitula per plant, number of seeds per capitula and 1,000-seed weight) and total chlorophyll content of cultivar IGPN 2004 was significantly higher in comparison to other cultivars given different FC% treatments (100, 80 and 60%). Significantly higher accumulation of proline, glycine betaine and total soluble sugars and lower damage to membrane lipids under increased water-deficit stress (i.e., at 80 and 60% FC) conditions in cultivar IGPN 2004 suggested its more tolerance capacity to water-deficit stress in comparison to other cultivars. Besides, antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase) partially demonstrated variations in the tolerance of the cultivars to water-deficit stress. The results suggest that cultivar IGPN 2004 could be considered as more tolerant, and IGP 76 and No. 71 as moderately tolerant, whereas GA 10 was more sensitive to water-deficit stress.     

Mannitol, polyethylene glycol and NaCl induced polypeptide changes during in vitro culture of three tomato cultivars

Three cultivars of tomato Pusa Ruby, Arka Vikas and Pusa Early Dwarf were subjected to osmotic stresses induced by mannitol, polyethylene glycol and NaCl in vitro. Polypeptide patterns were analyzed during each stress treatment to differentiate between tolerant and sensitive cultivars. The stresses induced more stress proteins in cv. Pusa Ruby compared to other two cultivars indicating it to be relatively osmotic stress tolerant.     

干旱胁迫对紫花苜蓿黄酮类化合物含量及其合成途径关键酶活性的影响

以3个紫花苜蓿(Medicago sativa)品种为试验材料,利用不同浓度(0、5%、10%、15％、20%、25%)的PEG 6000溶液模拟干旱胁迫,探究干旱胁迫对不同品种紫花苜蓿黄酮类化合物合成上游3个关键酶活性以及黄酮类化合物含量的影响。结果表明：(1)随着PEG 6000胁迫浓度的增加,3种紫花苜蓿叶片中PAL(苯丙氨酸解氨酶)、C4H(肉桂酸 4 羟基化酶)和4CL(4 香豆酸辅酶A连接酶)活性均呈先升高后降低的趋势,但不同酶类之间响应存在差异,即PAL活性在10% PEG 6000胁迫浓度下最高,C4H和4CL活性则在15% PEG 6000胁迫浓度下最高,且均显著高于相应对照。(2)3种紫花苜蓿植株地上部总黄酮含量和8种黄酮类化合物含量均随着PEG 6000胁迫浓度的增加呈先上升后下降的趋势,且均在10%~15% PEG 6000胁迫浓度时达到最高值,并显著高于相应对照。(3)各品种紫花苜蓿叶片黄酮类化合物含量与其关键酶活性呈不同程度的相关性,即紫花苜蓿黄酮类化合物合成途径上游3个关键酶活性与其地上部黄酮类化合物含量存在密切的关系。研究认为,不同程度的干旱胁迫可以通过促进黄酮类化合物合成途径上游关键酶活性的变化来调节紫花苜蓿植株中黄酮类化合物的合成,且适度干旱胁迫能显著促进相关酶活性增强和黄酮类化合物含量增加。     

Relationship between osmotic stress and polyamines conjugated to the deoxyribonucleic acid-protein in wheat seedling roots

The contents of covalently conjugated polyamines (CC-PAs) and noncovalently conjugated polyamines (NCC-PAs) to deoxyribonucleic acid-protein (DNP) isolated from wheat (Triticum aestivum L.) seedling roots under osmotic stress were detected. Results showed that after osmotic stress treatment for 7 d, the levels in NCC-spermine (NCC-Spm) and NCC-spermidine (NCC-Spd) of drought-tolerant Yumai No. 18 cv. increased more markedly than that of drought-sensitive Yangmai No. 9 cv., while the NCC-putrescine (NCC-Put) could not be statistically detected in two cultivars. Exogenous Spm treatment alleviated osmotic stress injury to Yangmai No. 9 cv. seedlings, coupled with marked increases of NCC-Spm and NCC-Spd levels of this cultivar. Under PEG osmotic stress, the concomitant treatment of drought-tolerant Yumai No. 18 cv.seedlings with methylglyoxyl-bis (guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), aggravated osmotic stress injury to this cultivar, coupled with market decreases of the NCC-Spm and NCC-Spd levels. The levels in CC-Put and CC-Spd of drought-tolerant Yumai No. 18 cv. increased more markedly than that of drought-sensitive Yangmai No. 9 cv. Under osmotic stress. The treatment of drought-tolerant Yumai No. 18 cv. seedlings with phenanthrolin (o-Phen), an inhibitor of transglutaminase (TGase), aggravated osmotic stress injury to this cultivar, coupled with a reduction of sum contents of CC-Put+CC-Spd. These results suggested that NCC-Spm and NCC-Spd, together with CC-Put and CC-Spd, in DNP of roots could enhance tolerance of the wheat seedlings to osmotic stress.     

Genotypic differences in the responses of gas exchange,chlorophyll fluorescence,and antioxidant enzymes to aluminum stress in <Emphasis Type="Italic">Festuca arundinacea</Emphasis>

In this study, the gas exchange, chlorophyll fluorescence, and antioxidant activity in eight tall fescue cultivars were investigated under aluminum stress. The results showed that the net photosynthetic rate (P _N) and stomatal conductance (g _s) were decreased, while the intercellular CO₂ concentration (C_i) was stable or increased under Al stress conditions. The efficiency of excitation capture by open PSII reaction centers (F′_v/F′_m), the maximum quantum yield of PSII photochemistry (F _v/F _m), the quantum yield of PSII electron transport (Φ_PSII), and the photochemical quenching (qP) were also decreased after Al stress, while the non-photochemical quenching (NPQ) was increased. Moreover, Al stress increased the antioxidant activities and MDA contents in each tall fescue cultivars. However, there was a lot genotype differences between the Al-tolerant and Al-sensitive cultivars. Cv. Barrington was the most sensitive cultivar and cv. Crossfire 2 was the most tolerant cultivar. The excessive excitation energy could not be dissipated efficiently by antenna pigments, and reactive oxygen species could not be scavenged efficiently, thereby resulting in membrane lipid peroxidation in cv. Barrington under Al stress conditions.     

Iso-osmotic effect of NaCl and PEG on growth, cations and free proline accumulation in callus tissue of two indica rice (Oryza sativa L.) genotypes

One-month old calli of two indica rice genotypes, i.e., Basmati-370 and Basmati-Kashmir were subjected to two iso-osmotic concentrations (−0.57 MPa and −0.74 MPa) created with 50 and 100 mol m⁻³ NaCl or 10 and 18% solutions of PEG-8000. Both genotypes tolerated only low levels of stress and showed severe growth suppression at −0.74 MPa. The degree of stress tolerance of both genotypes was greater for PEG induced stress than for NaCl induced stress. The relative growth rate of callus was reduced under both stresses, however, the reverse was true for callus dry weight. Sodium (Na⁺) content of the callus tissue was increased only under NaCl induced stress. Salt induced stress reduced K⁺ and Ca²⁺ contents, but the PEG induced stress increased them. Higher levels of stress increased the proline content many folds with more increase being under PEG stress than that under NaCl. Water and osmotic potentials of the callus tissue decreased, whereas turgor potential increased under both abiotic stresses. Overall, Basmati-370 was more tolerant to both NaCl and PEG induced stresses than Basmati-Kashmir, because of less reduction in growth and more dry weight. Moreover, Basmati-370 accumulated higher amounts of cations, free proline, and maintained maximum turgor as compared to Basmati-Kashmir. In conclusion, at cellular level, mechanism of NaCl induced osmotic stress tolerance was found to be associated with more ionic accumulation of inorganic solutes and that of PEG induced osmotic stress tolerance with the accumulation of free proline, as an important osmolyte in the cytosol.     

Accumulation and translocation of Cd metal and the Cd-induced production of glutathione and phytochelatins in <Emphasis Type="Italic">Vicia faba</Emphasis> L.

Translocation of cadmium (Cd) in the tissues of Vicia faba, the water content in biomass, the biomass production, and the glutathione and phytochelatin tissue concentrations were studied and correlated with the plant sensitivity and/or tolerance to Cd. The total concentrations of Cd were determined by inductively coupled plasma/mass spectrometry (ICP-MS), the concentrations of glutathione (GSH) and phytochelatins 2 and 3 (PC2 and PC3) were determined by on-line high performance liquid chromatography/electrospray-ionization tandem mass spectrometry (HPLC–ESI–MS–MS) in the roots and leaves of the sensitive and the tolerant cultivars of V. faba grown in Cd containing nutrient solutions (NS, 0–100 μmol l⁻¹ Cd²⁺). Both the cultivars of V. faba accumulate a major portion of Cd in the roots and only a minor part of ca. 4% in the leaves. The differences between the cultivars concerning Cd accumulation in leaves were apparent from higher Cd concentrations in NS and the Cd amount in the sensitive cultivar was approximately twice as high. In the roots, the differences between the cultivars in the Cd accumulation were only statistically significant with the highest Cd concentrations in NS, with the tolerant cultivar accumulating about 16% more of Cd compared to the sensitive one. The biomass production of the sensitive cultivar decreased approximately twice as fast with increasing Cd concentration in NS. The biomass water content decreased with increasing Cd concentration in NS in both the cultivars. In general, the GSH concentration did not linearly correlate with Cd accumulation, except for the roots of the sensitive cultivar where it was independent, and was higher in the sensitive cultivar than in the tolerant one in both the leaves and roots. The GSH concentration in leaves was approximately one order of magnitude higher than that in the roots for both the cultivars. The relationships between the PC and Cd concentrations in tissues were found nonlinear. At lower Cd accumulation levels, the PC concentrations followed an increase in the Cd accumulation in both the roots and leaves, whereas at higher Cd accumulations the relations differed between roots and leaves. In the roots, the PC concentrations decreased with increasing Cd accumulation, whereas the PC concentration in the leaves followed the decrease in the Cd accumulation.     

Does exogenous application of 24-epibrassinolide ameliorate salt induced growth inhibition in wheat (Triticum aestivum L.)?

A greenhouse experiment was conducted to assess whether exogenously applied 24-epibrassionlide (24-epiBL) could alleviate the adverse effects of salt on wheat. Two hexaploid wheat (Triticum aestivum L.) cultivars, S-24 (salt tolerant) and MH-97 (moderately salt sensitive), were grown under control (0 mM NaCl in full strength Hoagland’s nutrient solution) or saline conditions (150 mM of NaCl in full strength Hoagland’s nutrient solution). After 41 days growth of wheat plants under saline conditions, 24-epiBL was applied as a foliar spray. Four levels of BR were used as 0 (water spray), 0.0125, 0.025, and 0.0375 mg l⁻¹. Application of 24-epiBL increased plant biomass and leaf area per plant of both cultivars under non-saline conditions. However, under saline conditions, improvement in growth due to exogenous 24-epiBL was observed only in S-24. Photosynthetic rate was reduced due to salt stress in both cultivars, but this inhibitory effect was ameliorated significantly by the exogenous application of 24-epiBL. Exogenously applied 24-epiBL also enhanced the photosystem-II efficiency in both cultivars measured as F _v /F _m ratio. Although the activities of antioxidant enzymes, Superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) were increased due to salt stress in both wheat cultivars, exogenously applied 24-epiBL had a varying effect on the antioxidant system. The activity of SOD remained unaffected in both cultivars due to 24-epiBL application, but that of POD and CAT was promoted in the salt stressed plants of cv. S-24 only. In conclusion, improvement in growth in both wheat cultivars due to foliar applied 24-epiBL was found to be associated with 24-epiBL-induced enhancement in photosynthetic capacity. The 24-epiBL-induced regulation of antioxidant enzymes or growth under saline conditions was cultivar specific.     

Relationships between polyamines, ethylene, osmoprotectants and antioxidant enzymes activities in wheat seedlings after short-term PEG- and NaCl-induced stresses

Contents of ethylene, osmoprotectants, levels and forms of polyamines (PAs) and activities of antioxidant enzymes in the leaves and roots were investigated for five wheat cultivar seedlings (differing in drought tolerance) exposed to osmotic stress (?1.5 MPa). Stress was induced by 2-day-long treatment of plants with polyethylene glycol 6000 (PEG) or NaCl added to hydroponic cultures. Nawra, Parabola and Manu cv. (drought tolerant) showed a marked increase in osmoprotectors (proline and soluble carbohydrates, mainly glucose, saccharose and maltose), free PAs (putrescine Put, spermidine Spd and spermine Spm) and Spd-conjugated levels, in both leaves and roots, after PEG-treatments. Radunia and Raweta (drought sensitive) exhibited smaller changes in the content of these substances. The analysis of enzymes involved in proline metabolism revealed the glutamate as a precursor of proline synthesis in PEG-induced stress conditions. The increase in the activity of antioxidative enzymes, especially catalase and peroxidases, was characteristic for tolerant wheat plants, but for sensitive ones, a decrease in superoxide dismutase and an increase in mainly glutathione reductase activities were observed. After NaCl-treatment smaller changes of all biochemical parameters were registered in comparison with PEG-induced stress. Exceptions were the higher values of ethylene content and a significant increase in saccharose, raffinose and maltose levels (only in stress sensitive plants). The proline synthesis pathway was stimulated from both glutamate and ornithine precursors. These results suggest that the accumulation of inorganic ions in NaCl-stressed plants may be involved in protective mechanisms as an additional osmoregultor. Thus, a weaker stressogenic effect as determined as water deficit by leaf relative water content and relative dry weight increase rate and differences in metabolite synthesis in comparison with PEG stress was observed. Proline seems to be the most important osmo-protector in osmotic stress initiated by both PEG and NaCl. The synthesis of sugars and PAs may be stimulated in a stronger stress conditions (PEG).     

Reactive oxygen species, ascorbate–glutathione pool, and enzymes of their metabolism in drought-sensitive and tolerant indica rice (Oryza sativa L.) seedlings subjected to progressing levels of water deficit

Water deficit for rice is a worldwide concern, and to produce drought-tolerant varieties, it is essential to elucidate molecular mechanisms associated with water deficit tolerance. In the present study, we investigated the differential responses of nonenzymatic antioxidants ascorbate (AsA), glutathione (GSH), and their redox pool as well as activity levels of enzymes of ascorbate–glutathione cycle in seedlings of drought-sensitive rice (Oryza sativa L.) cv. Malviya-36 and drought-tolerant cv. Brown Gora subjected to water deficit treatment of ?1.0 and ?2.1 MPa for 24–72 h using PEG-6000 in sand cultures. Water deficit caused increased production of reactive oxygen species such as O₂?^?, H₂O₂, and HO? in the tissues, and the level of production was higher in the sensitive than the tolerant cultivar. Water deficit caused reduction in AsA and GSH and decline in their redox ratios (AsA/DHA and GSH/GSSG) with lesser decline in tolerant than the sensitive seedlings. With progressive level of water deficit, the activities of monodehydroascorbate reductase, dehydroascorbate reductase, ascorbate peroxidase (APX), and glutathione transferase increased in the seedlings of both rice cultivars, but the increased activity levels were higher in the seedlings of drought-tolerant cv. Brown Gora compared to the sensitive cv. Malviya-36. Greater accumulation of proline was observed in stressed seedlings of tolerant than the sensitive cultivar. In-gel activity staining of APX revealed varying numbers of their isoforms and their differential expression in sensitive and tolerant seedlings under water deficit. Results suggest that an enhanced oxidative stress tolerance by a well-coordinated cellular redox state of ascorbate and glutathione in reduced forms and induction of antioxidant defense system by elevated activity levels of enzymes of ascorbate–glutathione cycle is associated with water deficit tolerance in rice.     

Germination and growth of cultivars ofTrifolium subterraneum L. in the presence of sodium chloride salinity

Summary Germination and growth responses of 15 early to midseason cultivars ofTrifolium subterraneum L. were determined at a range of irrigation water salinities (NaCl). There were significant cultivar differences in seed germination under standard conditions in the presence of pure solutions of NaCl from −10 to −330 kPa osmotic potential range. There were also significant cultivar differences in growth on a clay loam soil with increasing NaCl over the same range of osmotic potentials as used to test germination. There was a generally poor correlation between salt tolerance at germination and at later stages of growth.     

Physiological responses of two Jerusalem artichoke cultivars to drought stress induced by polyethylene glycol

Physiological responses of two Jerusalem artichoke (Helianthus tuberosus L.) cultivars with different drought sensitivity to drought stress induced by polyethylene glycol (PEG) 6000 were investigated by characterizing water status, membrane lipid peroxidation, key antioxidant enzymes activity, and proline accumulation. It was observed that the drought-tolerant Jerusalem artichoke cv. Xiuyan maintained a relatively higher water status than the drought-sensitive cv. Yulin upon drought treatments. Meanwhile, lower levels of malondialdehyde (MDA) as well as higher levels of free proline occurred in cv. Xiuyan after 36 h drought treatments. Moreover, the activities of catalase (CAT) and superoxide dismutase (SOD) in cv. Xiuyan were higher than cv. Yulin after drought stress. These results indicated that drought sensitivities actually differ between Jerusalem artichoke cv. Xiuyan and cv. Yulin, and the cv. Xiuyan was more tolerant to drought stress caused by polyethylene glycol.     

Implication of ABA and proline on cell membrane injury of water deficit stressed barley seedlings

The aim of this work was to examine the ability of ABA and proline to counteract the deleterious effect of water deficit stress on cell membrane injuries. Six-day-old seedlings of two barley genotypes (cv. Aramir, line R567) were treated with ABA (2·10⁻⁴ M) or proline (0.1 M) for 24 h, and then subjected to osmotic stress for 24h, by immersing their roots in polyethylene glycol (PEG 6000) solution of osmotic potential of −1.0 MPa and −1.5 MPa or by submerging the leaf pieces in PEG solution of osmotic potential of −1.6 MPa. Pretreatment of plants with ABA and proline caused an increase of free proline level in the leaves. Plants treated with ABA exhibited a lower membrane injury index under water stress conditions than those untreated even when no effect of this hormone on RWC in the leaves of stressed plants was observed. Pretreatment of plants with proline prevented to some extent membrane damage in leaves of the stressed seedlings, but only in the case when stress was imposed to roots. Improvement in water status of leaves was also observed in seedlings pretreatment with proline. The protective effect of both ABA and proline was more pronounced in line R567 that exhibited higher membrane injury under water deficit stress conditions.