Physiological performance of two contrasting rice varieties under water stress

Two rice varieties PR-115 and Super-7 were imposed to water stress and different physiological traits were monitored to evaluate the performance of these varieties under drought. Under water stress condition although the relative water content, osmotic potential, chlorophyll content, photosynthesis rate, carbon discrimination and biomass decreased in both the varieties however, the reduction was more pronounced in Super-7 variety. Oryzanol a trans-ester of ferulic acid functions as antioxidant and it increased along with total phenolic and anthocyanin content in both the varieties under drought stress. However, gallic acid, 4 hydroxy benzoic acid, syringic acid and chlorogenic acid showed differential pattern in both of the varieties under water limiting conditions. Under drought, grain yield was penalized by 17 and 54% in PR-115 and Super-7 varieties, respectively in comparison to watered plants. Super-7 variety showed pronounced electrolyte leakage and MDA enhancement under water stress condition. High non photochemical quenching and reduction in Y(NO) and Y(II) indicated balanced energy management in tolerant PR-115 variety. The studies showed that PR-115 is a drought tolerant variety while Super-7 is drought sensitive in nature.     

Antioxidative protection and proteolytic activity in tolerant and sensitive wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) varieties subjected to long-term field drought

Field drought studies were performed in order to assess oxidative stress, proteolytic activity and yield loss under natural stress conditions. Flag leaves of two drought-tolerant (Yantar and Zlatitsa) and two drought-sensitive (Miziya and Dobrudjanka) winter wheat varieties were analyzed. Stress intensity was assessed by relative electrolyte leakage and proline accumulation. Senescence progression was followed by loss of chlorophyll and protein. Lipid peroxidation, H₂O₂ content, activities of superoxide dismutase (SOD), catalase (CAT), and non-specific peroxidase (GPX) isoforms, as well as proteolytic activities were analyzed from heading throughout grain filling. Weakening of membrane integrity and oxidative damage to lipids were more pronounced in the sensitive varieties under field drought. The activities of Fe- and Cu/Zn SOD isoforms decreased in the controls, but remained high in drought-treated plants. The activities of MnSOD isoforms and CAT were enhanced towards grain filling, especially in the sensitive varieties under drought. GPX activities were rised under drought but progressively diminished. Accelerated senescence under field drought was linked to higher proteolytic activity with variety specific differences in the protease response, but without a clear correlation to drought resistance or sensitivity. Field drought led to higher oxidative stress more pronounced for drought sensitive varieties, especially during the grain filling period.     

Effects of Drought Stress on Key Enzymes of Carbon Metabolism,Photosynthetic Characteristics and Agronomic Traits of Soybean at the Flowering Stage under Different Soil Substrates

Soybean is an important legume food crop, and its seeds are rich in nutrients, providing humans and animals with edible oil and protein feed. However, soybean is sensitive to water requirements, and drought is an important factor limiting soybean yield and quality. This study used Heinong 84 (drought resistant variety) and Hefeng 46 (intermediate variety) as tested varieties planted in chernozem, albic, and black soils. The effects of drought stress on the activities of key enzymes in carbon metabolism and photosynthetic characteristics of soybean were studied during the flowering stage, most sensitive to water. (1) The activities of SS-1, 6PGDH, and G6PDH enzymes in soybean leaves first increased and then decreased under drought stress. The enzyme activity was the highest under moderate drought stress and weakest in the blank group. (2) Drought stress increased Phi2, PhiNO, and Fm in soybean leaves and reached the highest value under severe drought; with the increase in drought stress, PhiNPQ and Fv/Fm of soybean leaves gradually decreased, reaching the lowest under severe drought. (3) With the increase in drought stress, F₀ and Fs of soybean leaves showed a single peak curve, and the maximum was at moderate drought. (4) Correlation analysis showed that F₀ was greatly affected by varieties and soil types; Fs, F0, and Fm soil varieties had a great influence, and chlorophyll fluorescence parameters were affected differently under drought stress with different drought degrees. (5) Drought stress changed the agronomic traits and yield of soybean. With the increase of drought degree, plant height, node number of main stem, effective pod number, 100-seed weight and total yield decreased continuously. (6) Drought stress affected the dry matter accumulation of soybean. With the increase of drought degree, the dry matter accumulation gradually decreased. Among them, the leaf was most seriously affected by drought, and SD decreased by about 55% compared with CK. Under the condition of black soil, the dry matter accumulation of soybean was least affected by drought.     

Comparative effect of water, heat and light stresses on photosynthetic reactions in Sorghum bicolor(L.) Moench

Five varieties of Sorghum bicolor (L.) Moench., differing in their drought tolerance under field conditions have been used to study the effect of individual components of drought stress, namely high light intensity stress, heat stress and water stress, on their photosynthetic performance. Chlorophyll content, chlorophyll fluorescence, ribulose-1,5-bisphosphate carboxylase (Rubisco, EC 4.1.1.39) content, phosphoenolpyruvate carboxylase (PEPcase, EC 4.1.1.31) activity and photo-synthetic oxygen evolution were used as key parameters to assess photosynthetic performance. The results indicated that photochemical efficiency of photosystem II (PSII) was severely reduced by all three stress components, whereas PEPcase activity was more specifically reduced by water stress. Degradation of Rubisco and chlorophyll loss occurred under high light and water stress conditions. Of the four drought-tolerant varieties, E 36-1 showed higher PEPcase activity, Rubisco content and photochemical efficiency of PSII, and was able to sustain a higher maximal rate of photosynthetic oxygen evolution under each stress condition as compared to the other varieties. A high stability to stress-induced damage, or acclimation of photosynthesis to the individual components of drought stress may contribute to the high yields of E 36-1 under drought conditions. In the E 36-1 variety markedly higher levels of the chloroplastic chaperonin 60 (cpn 60) were observed under all stress conditions than in the susceptible variety CSV 5.Key words: Chlorophyll fluorescence, drought stress, oxygen evolution, phosphoenopyruvate carboxylase, Sorghum.      

干旱胁迫对花生根系生长发育和生理特性的影响

以花育17号和唐科8号两个花生品种为试验材料,在防雨棚栽培池内进行土柱栽培试验,研究了中度干旱胁迫和正常供水处理下花生生育后期根系形态发育特征和生理特性.结果表明: 唐科8号具有较发达的根系及较高的产量和抗旱系数,花育17号根系对干旱胁迫的适应性小于唐科8号.两品种根长密度、根系生物量均主要分布于0～40 cm土层中,但同一土层内两品种根系性状存在差异.与正常供水处理相比,干旱胁迫处理使花育17号各生育期总根长、根系总表面积和总体积均降低,而唐科8号除花针期显著降低外,其余生育期均明显升高;干旱胁迫增加了两品种20～40 cm土层内根系生物量、根系表面积和体积,而降低了40 cm以下土层内各根系性状;干旱胁迫处理使两品种饱果期40 cm以下土层内根系活力降低,且花育17号降低幅度高于唐科8号.干旱胁迫下两品种生育后期根系发育和生理特性的差异表明其根系在干旱胁迫下对水分吸收和利用存在差异.     

Impact of drought stress on growth and quality of miscanthus for biofuel production

Miscanthus has a high potential as a biomass feedstock for biofuel production. Drought tolerance is an important breeding goal in miscanthus as water deficit is a common abiotic stress and crop irrigation is in most cases uneconomical. Drought may not only severely reduce biomass yields, but also affect biomass quality for biofuel production as cell wall remodeling is a common plant response to abiotic stresses. The quality and plant weight of 50 diverse miscanthus genotypes were evaluated under control and drought conditions (28 days no water) in a glasshouse experiment. Overall, drought treatment decreased plant weight by 45%. Drought tolerance – as defined by maintenance of plant weight – varied extensively among the tested miscanthus genotypes and ranged from 30% to 110%. Biomass composition was drastically altered due to drought stress, with large reductions in cell wall and cellulose content and a substantial increase in hemicellulosic polysaccharides. Stress had only a small effect on lignin content. Cell wall structural rigidity was also affected by drought conditions; substantially higher cellulose conversion rates were observed upon enzymatic saccharification of drought‐treated samples with respect to controls. Both cell wall composition and the extent of cell wall plasticity under drought varied extensively among all genotypes, but only weak correlations were found with the level of drought tolerance, suggesting their independent genetic control. High drought tolerance and biomass quality can thus potentially be advanced simultaneously. The extensive genotypic variation found for most traits in the evaluated miscanthus germplasm provides ample scope for breeding of drought‐tolerant varieties that are able to produce substantial yields of high‐quality biomass under water deficit conditions. The higher degradability of drought‐treated samples makes miscanthus an interesting crop for the production of second‐generation biofuels in marginal soils.     

Physiological response of wheat varieties to elevated atmospheric CO2 and low water supply levels

In the phytotron experiment, the effect of elevated atmospheric CO₂ (EC, 750 μmol mol^?1) on the drought tolerance was studied in two winter varieties (Mv Mambo, tolerant; Mv Regiment, moderately tolerant) and in one spring variety of wheat (Lona, sensitive to drought). Changes in net photosynthetic rate (P _N), stomatal conductance, transpiration, wateruse efficiency, effective quantum yield of photosystem II, and activities of glutathione reductase (GR), glutathione-Stransferase (GST), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were monitored during water withdrawal. Drought caused a faster decline of P _N at EC, leading to the lower assimilation rates under severe drought compared with ambient CO₂ (NC). In the sensitive variety, P _N remained high for a longer period at EC. The growth at EC resulted in a more relaxed activation level of the antioxidant enzyme system in all three varieties, with very low activities of GR, GST, APX, and POD. The similar, low values were due to decreases in the varieties which had higher ambient values. A parallel increase of CAT was, however, recorded in two varieties. As the decline in P _N was faster at EC under drought but there was no change in the rate of electron transport compared to NC values, a higher level of oxidative stress was induced. This triggered a more pronounced, general response in the antioxidant enzyme system at EC, leading to very high activities of APX, CAT, and GST in all three varieties. The results indicated that EC had generally favourable effects on the development and stress tolerance of plants, although bigger foliage made the plants more prone to the water loss. The relaxation of the defence mechanisms increased potentially the risk of damage due to the higher level of oxidative stress at EC under severe drought compared with NC.     

Physiological and morphological traits associated with adaptation of lucerne (Medicago sativa) to severely drought‐stressed and to irrigated environments

Adaptation to severe drought and to irrigated cropping can both contribute to increased water use efficiency of lucerne, but knowledge on the relevant adaptive traits is limited. Five cultivars featuring contrasting adaptive responses for 3‐year forage yield across 10 agricultural environments of the western Mediterranean basin were currently studied, to identify physiological and morphological traits associated with specific and wide‐adaptation responses. The landraces Mamuntanas, Demnat 203 and Erfoud 1, and the varieties SARDI 10 and Prosementi, were grown in replicated metal containers (55 cm long × 12 cm wide × 75 cm deep; 21 plants per container) under irrigation (weekly restoring soil field capacity) and under moderate and severe drought stress (implying decreased irrigation for 30 days followed by withheld irrigation for 33 and 58 days, respectively). Cultivar post‐stress survival reflected the known cultivar adaptation to drought‐prone agricultural environments. Demnat 203, specifically adapted to irrigated, frequently mown environments, displayed higher amounts of starch, soluble proteins and total nitrogen in the crown and the root under irrigation. This was due to outstanding organ size and, for starch, higher concentrations. Mamuntanas, specifically adapted to drought‐prone environments, exhibited high water‐soluble carbohydrate concentration in storage organs under severe stress, along with a water‐conservation strategy implying less water used in initial drought‐stress phases due to limited early root development that resulted in more water available under severe stress. Drought‐tolerant germplasm also displayed lower wilting under early stress, more plants with green tissues under severe stress, and more stems per plant in stress or favourable conditions. Multivariate patterns of cultivar variation for physiological and morphological traits were strictly associated with cultivar variation for adaptation pattern. Our results highlighted the difficulty to combine some traits of environment‐specific adaptive value into a unique widely adapted variety, supporting the selection of varieties specifically adapted to irrigated or severely drought‐prone environments.     

不同抗旱性花生品种的根系形态发育及其对干旱胁迫的响应

为明确不同抗旱性花生品种的根系形态发育特征,探讨其根系形态发育特征对不同土壤水分状况的响应机制,在防雨棚旱池内进行土柱栽培试验,研究抗旱型品种“花育22号”、“唐科8号”和干旱敏感型品种“花育23号”3个不同抗旱性花生品种根系形态发育特征及其对干旱胁迫的响应.结果表明:抗旱型品种根系较发达,具有较大的根系生物量、总根长、总根系表面积.干旱胁迫使抗旱型品种根系总表面积和体积增加,而干旱敏感型品种则相反.干旱胁迫显著增加抗旱型品种“花育22号”20 cm以下土层内根长密度分布比例及根系表面积和体积,但“唐科8号”相应根系性状仅在20-40 cm土层内增加;干旱胁迫使干旱敏感型品种“花育23号”40 cm以下土层内各根系性状升高,但未达显著水平且其深层土壤内各根系性状增加幅度小于“花育22号”.花生根系总长、总表面积及0-20 cm土层内根系性状与产量间呈显著或极显著正相关.土壤水分亏缺条件下,花生主要通过增加深层土壤内根长、根系表面积和体积等形态特性,优化空间分布构型,以调节植株对水分的利用.     

不同倍性冬小麦种内竞争能力的比较研究

通过3个不同倍性冬小麦材料(两倍体栽培一粒、四倍体栽培两粒、六倍体现代品种长武134),在不同水分条件下进行密度实验,研究了不同材料的株高、生物量累积和分蘖动态的变化,以及产量对密度变化的反应。结果表明随着群体的增大,不同倍性材料个体间竞争明显加剧,相互抑制作用增强,种群内部个体大小等级差异增大;在不同群体下各倍性材料的个体生长存在差异,表现为四倍体栽培两粒竞争能力两倍体栽培一粒六倍体现代品种长武134,且长武134受种群大小影响最为显著,但长武134产量累积的投入比例最高,产量最高,低竞争能力的个体更适合生产上的需求,是群体高产的基础。研究结果为旱地小麦的高产栽培和育种提供了理论基础。     

辣椒开花结果期对干旱胁迫的形态与生理响应

在遮雨网室选用抗旱性较强的农城椒二号和抗旱性较弱的陕蔬2001,研究辣椒在轻度、中度和重度干旱胁迫下不同时间的生长、产量、渗透调节物质、保护酶活性的变化规律及其生理调节机制。结果表明:随干旱胁迫时间的延长,辣椒的株高、分枝数、叶面积、单位面积产量、叶绿素含量和叶片相对含水量的抗旱系数呈下降趋势,下降速率与干旱胁迫程度呈正相关,与品种的抗旱性呈负相关;脯氨酸、丙二醛含量和细胞膜透性相对值随干旱胁迫时间的延长呈上升趋势;POD、SOD、CAT活性和可溶性蛋白相对值随着干旱胁迫时间的延长先升高后下降,抗旱性强的材料增加幅度低于抗旱性弱的材料;可溶性糖含量的相对值在轻度和中度干旱胁迫下呈上升趋势,在重度干旱胁迫下呈上升—下降趋势,且抗旱性强的材料上升速度大于抗旱性弱的材料。相关分析表明,干旱胁迫下,产量与株高、分枝数、叶片叶绿素含量、叶面积、叶片相对含水量抗旱系数呈显著正相关;与细胞膜透性、CAT活性和可溶性蛋白含量抗旱系数呈显著负相关。主成分分析表明,用作辣椒抗旱性鉴定的主要指标是单株产量、株高、叶面积、分枝数、可溶性蛋白、可溶性糖、MDA、叶绿素含量和细胞膜透性及叶片相对含水量,叶片POD、SOD、CAT活性、脯氨酸含量可做为辣椒抗旱性鉴定的次要鉴选指标。     

干旱胁迫及复水对不同黍稷品种根系生理特性的影响

以2种抗旱性不同的黍稷品种(‘陇糜4号’和‘晋黍7号’)为试验材料,采用盆栽试验研究了苗期中度和重度干旱胁迫后拔节期复水对其根系生理特性的影响。结果显示:(1)干旱胁迫引起2个黍稷品种根系活力明显下降,根系SOD、POD活性以及MDA、脯氨酸含量明显升高,而且重度干旱胁迫处理变化幅度显著大于中度干旱胁迫。(2)复水后,2个黍稷品种根系的各项生理指标均有不同程度的恢复,且中度胁迫处理较易恢复,重度胁迫下恢复能力很弱。(3)2个黍稷品种根系各项生理指标在干旱胁迫及复水条件下变化幅度不同,干旱胁迫下抗旱性强的‘陇糜4号’根系活力下降幅度明显低于抗旱性弱的‘晋黍7号’,根系SOD活性、POD活性、MDA含量和脯氨酸含量的上升幅度明显高于‘晋黍7号’,而复水后‘陇糜4号’根系的各项生理指标的恢复能力明显强于‘晋黍7号’。研究表明,干旱胁迫及复水条件下‘陇糜4号’均表现出较高的根系活力、保护酶活性和脯氨酸含量,且MDA含量较低,从而表现出较强的抗旱性。     

Proline accumulation: A parameter for evaluation of sensitivity of tomato varieties to drought stress?

The pattern of proline accumulation and the growth response were followed in several tomato ( Lycopersicon esculentum Mill.) varieties which were exposed to 7 days of drought stress followed by a 15-day period of rewatering. During dehydration, water potential and leaf elongation rates decreased more in var. 'Hosen' and 'S-5' than in 'LX-11', '1970', 'Pakmor', 'Faculty-16', 'Alcobaca' and '475'. Proline accumulation during stress was greatest in the first two varieties. In 'Hosen' and 'S-5' rewatering resulted in a decrease of proline to control levels, whereas in the other varieties accumulation of proline continued long after turgor had been regained. The extent of this continued accumulation was not correlated with the degree to which each variety was dehydrated. Upon rewatering of the plants the rate of leaf elongation was increased, but the final leaf size as well as whole shoot and root fresh weight of the recovered plants were not colated with the degree of "suffering" that each variety experienced during the drought period. Incubation of detached young tomato leaves in polyethylene glycol solution for 48 h resulted in a substantial accumulation of proline. The varietal differences observed under these conditions were reminiscent of the differential responses in proline accumulation obtained in the intact plants. It is concluded that proline accumulation at the time of dehydration signals drought stress in tomato plants but does not correlate with the overall varietal sensitivity to transient dehydration in recovered plants.     

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.     

Antioxidative response in different sorghum species under short-term salinity stress

Seedlings of sorghum varieties (M35-1, a drought tolerant species; SPV-839, a drought sensitive one) differing in their drought tolerance were subjected to 150 mM NaCl stress for a short duration of time (up to 72 h). Both the varieties failed to exhibit efficient ion exclusion mechanism like that of salt tolerant species, but in turn resulted in higher accumulation of Na⁺ and Cl⁻ ions over a period of 72 h salt stress. In addition, accumulation of calcium, potassium and proline in seedlings of sorghum varieties was moderate to short-term NaCl stress. The modulation of antioxidant components significantly diverged between the two varieties during seed germination, further the efficiency of antioxidant scavenging system is maintained during short-term NaCl treatments. In comparison to tolerant variety, the sensitive variety depicted higher SOD activity under control and salinity treatments but specific activity of catalase was significantly reduced. In contrast, drought tolerant variety exhibited efficient hydrogen peroxide scavenging mechanisms with higher catalase and GST activities under control and salt stress conditions, but not in the sensitive one. In conclusion, our comparative studies indicate that drought tolerant and susceptible varieties of sorghum induce efficient differential oxidative components of enzymatic machinery for scavenging ROS thereby alleviating the oxidative stress generated by salt stress during seedling growth.     

Antioxidant system is essential to increase drought tolerance of sugarcane

Drought is one of the main factors affecting the productivity of agricultural crops, and plants respond to such stress by activating various physiological and biochemical mechanisms against dehydration. The present study investigated two varieties of sugarcane (Saccharum spp.) with contrasting responses to drought (RB867515, more tolerant; and RB855536, less tolerant) and subjected them to progressive drought conditions (2, 4, 6 and 8 days) followed by rehydration. Drought caused a decrease in water potential (ψ_w) and osmotic potential (ψ_os) in the leaves, which recovered to normal levels after rehydration only up to the fourth day of drought. Water stress changed the carbon metabolism of leaves by reducing starch and sucrose contents and increasing glucose and fructose contents in both varieties. Water deficit caused a significant reduction in the maximum quantum efficiency of photosystem II (F_v/F_m) and effective quantum yield (Φ_PSII) in both varieties; however, RB867515 recovered faster after rehydration. Under water stress, the more tolerant variety RB867515 exhibited increased activity of the antioxidant enzymes catalase, ascorbate peroxidase and superoxide dismutase compared with the RB855536 variety. The results suggest that RB867515 is more tolerant to drought conditions because of a more efficient antioxidant system, which results in reduced photosynthesis photoinhibition during water stress, thus revealing itself as a potential physiological marker for drought tolerance studies.     

The effect of drought on the development and yielding of two different varieties of the fodder broad bean (Vicia faba minor)

A factorial experiment was performed in the fodder broad bean to analyse effects of soil drought on the development and yield components of two varieties of different morphotype: 'Nadwi?lański' (traditional) and 'Tim' (determinate growth habit). Plants were grown in Mitscherlich's pots under three different soil moistures: 70%, 50% and 30% of field water capacity. The soil water shortage contributed to a considerable depression in the developmental characteristics and yield traits of both varieties. Under all conditions, the variety 'Nadwi?lański yielded more seeds than did 'Tim'. The traditional variety was more resistant to drought than the new 'Tim'.