Genotypic variation in drought stress response and subsequent recovery of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Three wheat (Triticum aestivum L.) genotypes, Sadovo, Katya and Prelom, with different tolerance to drought were comparatively evaluated in terms of leaf respiratory responses to progressing dehydration and consecutive rewatering. Under drought stress, the respiration of all varieties gradually decreased, as the drought-tolerant Katya showed the most pronounced decline at earlier stages of dehydration. When water stress intensified, this genotype gave relatively stable respiration rates compared with the drought-sensitive varieties. Additionally, dehydrated Katya leaves displayed lower stomatal conductance and higher photosynthesis values, which resulted in greater water use efficiency during the dehydration period. Combination of drought stress and short-term changes in leaf temperature also induced genotype-specific response that differed from the response to drought only. Over the whole temperature range, the leaves of Katya exposed to dehydration for 14 days, showed higher respiration rates compared to the drought-sensitive varieties. The sensitive varieties maintained higher respiration rates under control conditions and mild dehydration, and very low rates under severe drought. In Katya, respiration and photosynthesis were fully restored from the stress within the first day of rewatering. The drought-sensitive genotypes displayed a considerably slower recovering capacity. The results are discussed in terms of possible physiological mechanisms underlying plant tolerance to drought.     

Drought,high temperature,and their combination affect ultrastructure of chloroplasts and mitochondria in wheat (Triticum aestivum L.) leaves

Plants experience a number of limiting factors, as drought and heat, which are often coinciding stress factors in natural environment. This study evaluated the changes in mesophyll cell ultrastructure in the leaves of two varieties of winter wheat (Triticum aestivum L.), differing in their drought tolerance, under individual or combined drought and heat treatment. Although the individual stress factors affected leaf ultrastructure, the damaging effect of the combined drought and heat was more pronounced and manifested certain differences between genotypes. Chloroplasts and mitochondria were affected in a variety-specific manner under all adverse treatments. The organelles of the drought-tolerant Katya were better preserved than those in the sensitive variety Sadovo. Leaf ultrastructure can be considered as one of the important characteristics in the evaluation of the drought susceptibility of different wheat varieties.     

水分胁迫对甘蔗叶片线粒体膜流动性的影响及其与膜脂过氧化的关系

用荧光探剂ANS对抗旱性不同的甘蔗品种在水分胁迫下叶片线粒体膜流动性的变化进行的研究表明,水分胁迫降低了线粒体膜的流动性,抗旱性强的甘蔗品种Co 617和F.Y.79-9的下降幅度分别小于抗旱性弱的Co 740和M.T.77-208;水分胁迫下线粒体膜流动性的下降与膜脂过氧化产物丙二醛含量的增加有密切关系。外源自由基处理试验也表明,甘蔗叶片线粒体膜流动性的下降与膜脂过氧化作用有关。     

Drought stress effects on Rubisco in wheat: changes in the Rubisco large subunit

The leaf protein pattern from drought-tolerant and drought-sensitive wheat varieties subjected to severe soil drought but with the possibility for recover from stress was studied by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). The spots representing Rubisco large subunit (RLS) were identified using polyclonal antibodies against Rubisco and immunoblotting. Some qualitative and quantitative differences in the 2D-PAGE protein map of wheat varieties were revealed under drought conditions. Three days recovery of wheat plants were not enough for restoring RLS quantity to the level of controls after 7 days drought, especially in the drought-sensitive variety Miziya. There are contradictory data in the literature concerning increased or diminished RLS level in drought stressed plants. A comparison of RLS after SDS-PAGE and 2D-PAGE was made. The revealed protein pattern depended on the presence or absence of protease inhibitors in the extraction buffer, on the procedure of extraction, and on the degree of stress.     

The Response Difference of Mitochondria in Recalcitrant Antiaris toxicaria Axes and Orthodox Zea mays Embryos to Dehydration Injury

Long-term preservation of recalcitrant seeds is very difficult because the physiological basis on their desiccation sensitivity is poorly understood. Survival of Antiaris toxicaria axes rapidly decreased and that of immature maize embryos very slowly decreased with dehydration. To understand their different responses to dehydration, we examined the changes in mitochondria activity during dehydration. Although activities of cytochrome (Cyt) c oxidase and malate dehydrogenase of the A. toxicaria axis and maize embryo mitochondria decreased with dehydration, the parameters of maize embryo mitochondria were much higher than those of A. toxicaria, showing that the damage was more severe for the A. toxicaria axis mitochondria than for those of maize embryo. The state I and III respiration of the A. toxicaria axis mitochondria were higher than those of maize embryo, the former rapidly decreased, and the latter slowly decreased with dehydration. The proportion of Cyt c pathway to state III respiration for the A. toxicaria axis mitochondria was low and rapidly decreased with dehydration, and the proportion of alternative oxidase pathway was high and slightly increased with dehydration. In contrast, the proportion of Cyt c pathway for maize embryo mitochondria was high, and that of alternative oxidase pathway was low. Both pathways decreased slowly with dehydration.     

Effect of Temperature on Rates of Alternative and Cytochrome Pathway Respiration and Their Relationship with the Redox Poise of the Quinone Pool

We investigated the effect of short-term changes in temperature on alternative (Alt) and cytochrome (Cyt) pathway respiration, both in intact tissues and isolated mitochondria of 14-d-old cotyledons of soybean (Glycine max L. cv Stevens). We also established the extent to which temperature alters the interaction between the oxidizing pathways and the level of ubiquinone (UQ) reduction (UQ(r)/UQ(t)). No difference was found between the temperature coefficient of respiration (Q(10); proportional change per 10 degrees C) of Alt and Cyt pathway respiration in cotyledon slices (Q(10) = 1.92 and 1.86, respectively). In isolated mitochondria, the Q(10) of the fully activated Alt pathway (Q(10) = 2.24-2.61) was always equal to, or higher than, that of Cyt c oxidase (COX) alone (Q(10) = 2.08) and the complete Cyt pathway (Q(10) = 2.40-2.55). This was true regardless of substrate or whether ADP was present. There was little difference in the Q(10) of the Cyt pathway with or without ADP; however, the Q(10) of COX was substantially lower in the presence of an uncoupler (Q(10) = 1.61) than its absence (Q(10) = 2.08). The kinetics of Alt and Cyt pathway activity in relation to UQ(r)/UQ(t) were not affected by temperature. For a given UQ(r)/UQ(t) value, the proportion of maximum flux taking place was similar at all temperatures for both pathways (+/-ADP). However, the Q(10) of the Alt and the Cyt pathways (+ADP) increased with increasing UQ(r)/UQ(t). We conclude that the Alt pathway is not less temperature sensitive than the Cyt pathway or COX per se and that changes in the degree of control exerted by individual steps in the respiratory apparatus could result in changes in the Q(10) of mitochondrial O(2) uptake.     

干旱胁迫对不同耐旱性大麦品种叶片超微结构的影响

选用耐旱性不同的3个大麦(Hordeum sativum)品种作为研究对象, 分析干旱胁迫对其叶肉细胞叶绿体、线粒体和细胞核超微结构的影响。结果表明, 3个大麦品种在非胁迫条件下其超微结构无明显差异。遭受干旱胁迫后, 不耐旱大麦品种Moroc9-75叶片细胞核中染色质的凝聚程度高, 叶绿体变形, 外被膜出现较大程度的波浪状和膨胀, 同时基粒出现弯曲、膨胀、排列混乱的现象; 线粒体外形及膜受到破坏、内部嵴部分消失等。耐旱大麦品种HS41-1叶片细胞中染色质虽出现凝聚, 但凝聚程度低; 其叶绿体及线粒体与非胁迫条件下基本相似, 多数未见明显损伤。耐旱中等的大麦品种Martin叶片超微结构的变化则介于二者之间。因此, 干旱胁迫下叶绿体外形、基粒和基质类囊体膜结构的完整性与基粒的排列次序、染色质的凝聚度和线粒体膜及嵴的完整性与大麦的耐旱性相关, 这些特性可作为评价大麦耐旱性强弱的形态结构指标。     

Physiological and biochemical tools useful in drought-tolerance detection in genotypes of winter triticale: accumulation of ferulic acid correlates with drought tolerance

BACKGROUND AND AIMS: The objectives of this study were to investigate whether a classification of triticale genotypes into drought-tolerant and drought-sensitive types based on field performance trials correlates with a classification based on measurements of some physiological and biochemical parameters in greenhouse conditions. In addition, an examination was carried out of whether ferulic acid, as the main origin of the blue fluorescence produced, contributes to drought tolerance. METHODS: Ten winter triticale genotypes were examined, five known to be drought tolerant and five drought sensitive. Measurements of the osmotic potential, leaf gas exchange, chlorophyll fluorescence, and blue and red fluorescence were performed. In addition, analysis of the total pool of phenolic compounds and ferulic acid as well as the measurements of PAL (l-phenylalanine ammonia-lyase) activity were carried out. KEY RESULTS: In agreement with field trials, three out of five cultivars ('Lamberto', 'Timbo' and 'Piano') were classified as drought tolerant. However, in the case of cultivar 'Babor', included in the group of drought-sensitive cultivars, the values obtained for some measured parameters were close to (F(v)(')/F(m)('), phenolics content, osmotic potential) or even better than (non-photochemical quenching, red and blue fluorescence, ferulic acid content) those for drought-tolerant genotypes. Cultivars 'Imperial', 'Ticino', 'Trimaran' and 'Boreas' were included in the drought-sensitive group, whereas cultivars 'Focus' and 'Kitaro' were included in the moderately sensitive group. CONCLUSIONS: The experiments confirmed that the period of flowering, the critical phase for plants as far as water demand is concerned, is suitable for plant screening and differentiation due to their tolerance to drought. The most important criteria which enabled creation of the ranking list of plants, from those sensitive to drought to those tolerant to drought, were the ability to perform the process of osmoregulation, the efficiency of the utilization of excitation energy by the photosynthetic apparatus and the functioning of protective mechanisms involving the level of ferulic acid in leaf tissues.     

Photochemical responses and oxidative stress in two clones of Coffea canephora under water deficit conditions

The effects of water deficit on photochemical parameters and activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as, cellular damages were investigated in two clones of Coffea canephora differing in drought tolerance. After 6 days without irrigation, predawn leaf water potential fell to −3.0 MPa that was accompanied by the suppression of net photosynthesis in both clones. The variable to maximum chlorophyll fluorescence ratio remained unchanged regardless of the imposed treatments. Both clones showed a similar decline (about 25%) in the photochemical quenching coefficient, but only the drought-sensitive clone exhibited an enhancement (31%) of thermal deactivation under water deficit conditions. The quantum yield of electron transport decreased similarly in both genotypes. Under drought conditions, activities of SOD, CAT and APX increased to a greater extent in the drought-tolerant clone than in the drought-sensitive one. This seemed to be matched with higher protection against oxidative stress, as judged from the lower levels of lipid peroxidation and electrolyte leakage in the drought-tolerant clone. Thus, the ability to increase the antioxidant system activity in order to limit cellular damages might be an important attribute linked to the drought tolerance in C. canephora.     

Comparative analysis of DNA methylation changes in two contrasting wheat genotypes under water deficit

DNA methylation is one of the epigenetic mechanisms regulating gene expression in plants in response to environmental conditions. In this study, analysis of methylation patterns was carried out in order to assess the effect of water stress in two contrasting wheat genotypes using methylation-sensitive amplified polymorphism (MSAP). The results revealed that demethylation was higher in drought-tolerant genotype (C306) as compared to drought-sensitive genotype (HUW468) after experiencing drought stress. Comparisons of different MSAP patterns showed a high percentage of polymorphic bands between tolerant and susceptible wheat genotypes (from 74.79 % at anthesis to 88.89 % at tillering). Furthermore, differential DNA methylation in roots and leaves also revealed tissue-specific methylation of genomic DNA. Interestingly, 54 developmental stage-specific bands and 23 bands that were found contrasting between these two wheat genotypes were detected. Furthermore, a few sites with stable DNA methylation differences were identified between drought-tolerant and drought-sensitive cultivars, thus providing genotype-specific epigenetic markers. These results not only provide data on differences in DNA methylation changes but also contribute to dissection of molecular mechanisms of drought response and tolerance in wheat.     

Expression of selected heat shock proteins after individually applied and combined drought and heat stress

Drought and heat stress are among the abiotic factors causing the most severe damage on plant crops. Their combination is quite common in dry and semi-dry regions worldwide and little is known about its effect on heat shock protein (HSP) profile in wheat plants. The expression of four HSP genes (Hsp 17.8, Hsp 26.3, Hsp 70 and Hsp 101b) in Triticum aestivum L. plants subjected to individually applied water deprivation or high temperature and their combination was monitored via one-step RT-PCR analysis. Changes in the expression levels of small HSPs (smHSPs), HSP70 and HSP100 were established also by SDS-PAGE. The combination of drought and heat induced HSP expression more effectively than the individually applied stresses. The induction of HSPs displayed greater rate in the drought-tolerant wheat variety Katya than in the drought-sensitive cv. Sadovo. The results obtained in wheat plants suggested that the effect of separately applied drought and heat shock cannot be extrapolated to their combination.     

Aerenchyma development in different root zones of maize genotypes under water limitation and different phosphorus nutrition

Root cortical aerenchyma (RCA) is suggested to reduce metabolic cost for root growth, but it might lower water uptake by plants. The objective of this work was to evaluate the effects of drought and phosphorus on the RCA development along the root axis and to elucidate its role in water stress tolerance of two maize genotypes. Plants of drought-tolerant DKB390 and drought-sensitive BRS1010 genotypes were grown in Vermiculite at field capacity of 100, 75, 50, and 25 % and supplied with 0.1, 0.4, and 0.8 mM phosphorus. Growth parameters, RCA, and plant P content were evaluated for all plants. Higher RCA development was observed in DKB390 than in BRS1010. Drought reduced the percentage of RCA in the root-hair zone of both genotypes but increased its development in the root maturation zone. Phosphorus limitation enhanced RCA development only in the DKB390. Under drought stress, DKB390 showed resilient growth whereas growth was inhibited in BRS1010. Higher root P content was related to its higher supply. Therefore, RCA formation was induced either by drought or by phosphorus limitation, while no interaction was evident. The RCA development varied along the root axis in order to balance water and phosphorus uptake and the drought response was genotype dependent.     

水稻幼苗叶绿体保护系统对干旱的反应

干旱条件下水稻耐旱品种湘中籼２号比不耐旱品种湘早籼１２号具有较低的质膜相对透性、叶绿素含量降低较少,表明耐旱品种受伤害较轻,两个品种的抗坏血酸。过氧化物酶（ＡｓＡ－ＰＯＤ）均降低,但耐旱品种降低较少。耐旱品种的谷胱甘肽还原酶（ＧＲ）活性在干旱初期提高,不耐旱品种的则变化不大。０．０１ｍｍｏｌ／Ｌ的百草枯和０．１ｍｍｏｌ／Ｌ的Ｈ２Ｏ２亦能诱导耐旱品种的ＧＲ活性,但对不耐旱品种的ＧＲ活性不受影响,说明可能是干旱诱导的氧化胁迫诱导了ＧＲ活性。干旱条件下两品种的抗坏血酸（ＡｓＡ）和还原型谷胱甘肽（ＧＳＨ）含量均是先升后降,但耐旱品种提高幅度较大。结果表明,耐旱品种的叶绿体保护系统的活性比不耐旱品种的高。     

干旱胁迫对不同耐旱性大麦品种叶片超微结构的影响

选用耐旱性不同的3个大麦（Hordeum sativum）品种作为研究对象,分析干旱胁迫对其叶肉细胞叶绿体、线粒体和细胞核超微结构的影响。结果表明,3个大麦品种在非胁迫条件下其超微结构无明显差异。遭受干旱胁迫后,不耐旱大麦品种Moroc9-75叶片细胞核中染色质的凝聚程度高,叶绿体变形,外被膜出现较大程度的波浪状和膨胀,同时基粒出现弯曲、膨胀、排列混乱的现象;线粒体外形及膜受到破坏、内部嵴部分消失等。耐旱大麦品种HS41-1叶片细胞中染色质虽出现凝聚,但凝聚程度低;其叶绿体及线粒体与非胁迫条件下基本相似,多数未见明显损伤。耐旱中等的大麦品种Martin叶片超微结构的变化则介于二者之间。因此,干旱胁迫下叶绿体外形、基粒和基质类囊体膜结构的完整性与基粒的排列次序、染色质的凝聚度和线粒体膜及嵴的完整性与大麦的耐旱性相关,这些特性可作为评价大麦耐旱性强弱的形态结构指标。     

Early osmotic adjustment responses in drought- resistant and drought-sensitive oilseed rape

The impact of osmotic stress on growth, physiolo- gy, and metabolism of winter oilseed rape （Brassica napus L.） was investigated by detailed analysis of biomass traits, hormone metabolites and osmolytes in two genetically unrelated drought-tolerant genotypes and two unrelated drought-sensitive genotypes. Seedlings were grown in vitro under controlled conditions and osmotic stress was simulated by applying a gradual treatment with polyethylene glycol （PEG 6ooo）, followed by hypo-osmotic treatment of variants used for metabolite determination. The results provide a basis for the identification of reliable selection criteria for drought resistance in oilseed rape. The in vitro cultivation system established during this study enabled effective discrimination of early osmotic stress responses between drought-resistant and -susceptible oilseed rape genotypes that also show large differences in relative seed yield under drought conditions in the field. Clear physiological and metabolic differences wereobserved between the drought-resistant and drought-sensitive genotypes, suggesting that osmotic adjustment is a key component of drought response in oilseed rape. Unexpected- ly, however, the drought-resistant genotypes did not show typical hormonal adjustment and osmolyte accumulation, suggesting that they possess alternative physiological mech- anisms enabling avoidance of stress symptoms.     

Early osmotic adjustment responses in drought-resistant and drought-sensitive oilseed rape

The impact of osmotic stress on growth, physiology, and metabolism of winter oilseed rape(Brassica napus L.)was investigated by detailed analysis of biomass traits,hormone metabolites and osmolytes in two genetically unrelated drought-tolerant genotypes and two unrelated drought-sensitive genotypes. Seedlings were grown in vitro under controlled conditions and osmotic stress was simulated by applying a gradual treatment with polyethylene glycol(PEG6000), followed by hypo-osmotic treatment of variants used for metabolite determination. The results provide a basis for the identification of reliable selection criteria for drought resistance in oilseed rape. The in vitro cultivation system established during this study enabled effective discrimination of early osmotic stress responses between drought-resistant and -susceptible oilseed rape genotypes that also show large differences in relative seed yield under drought conditions in the field. Clear physiological and metabolic differences were observed between the drought-resistant and drought-sensitive genotypes, suggesting that osmotic adjustment is a key component of drought response in oilseed rape. Unexpected ly, however, the drought-resistant genotypes did not show typical hormonal adjustment and osmolyte accumulation suggesting that they possess alternative physiological mech anisms enabling avoidance of stress symptoms.     

The synergistic effect of drought and light stresses in sorghum and pearl millet

The effects of drought stress and high irradiance and their combination were studied under laboratory conditions using young plants of a very drought-resistant variety, ICMH 451, of pearl millet (Pennisetum glaucum) and three varieties of sorghum (Sorghum bicolor)—one drought-resistant from India, one drought-tolerant from Texas, and one drought-sensitive variety from France. CO₂ assimilation rates and photosystem II fluorescence in leaves were analyzed in parallel with photosynthetic electron transport, photosystem II fluorescence, and chlorophyll-protein composition in chloroplasts isolated from these leaves. High irradiance slightly increased CO₂ assimilation rates and electron transport activities of irrigated plants but not fluorescence. Drought stress (less than −1 megapascal) decreased CO₂ assimilation rates, fluorescence, and electron transport. Under the combined effects of drought stress and high irradiance, CO₂ assimilation rates and fluorescence were severely inhibited in leaves, as were the photosynthetic electron transport activities and fluorescence in chloroplasts (but not photosystem I activity). The synergistic or distinctive effect of drought and high irradiance is discussed. The experiments with pearl millet and three varieties of sorghum showed that different responses of plants to drought and light stresses can be monitored by plant physiological and biochemical techniques. Some of these techniques may have a potential for selection of stress-resistant varieties using seedlings.