Drought-induced expression of aquaporin genes in leaves of two common bean cultivars differing in tolerance to drought stress

Aquaporin proteins are part of the complex response of common bean (Phaseolus vulgaris L.) to drought which affects the quality and quantity of yield of this important crop. To better understand the role of aquaporins in common bean, drought-induced gene expression of several aquaporins was determined in two cultivars, the more drought tolerant Tiber and the less tolerant Starozagorski ?ern. The two bean cultivars were selected among 16 European genotypes based on the tolerance to drought determined by time needed for plants to wilt after withholding irrigation and yield at harvest. The expression patterns of two plasma membrane intrinsic proteins, PvPIP1;2 and PvPIP2;7, and two tonoplast intrinsic proteins, PvTIP1;1 and PvTIP4;1 in leaves of 21 day old plants were determined by RT-qPCR in both cultivars under three degrees of drought stress, and under rehydration and control conditions. Gene expression of all four examined aquaporins was down-regulated in drought stressed plants. After rehydration it returned to the level of control plants or was even higher. The responses of PvPIP2;7 and PvTIP1;1 during drought and rehydration were particularly pronounced. The gene expression of PvPIP2;7 and PvTIP4;1 during drought was cultivar specific, with greater down-regulation of these two aquaporins in drought tolerant Tiber. Under drought stress the relative water content and water potential of leaves were higher in Tiber than in Starozagorski plants. The differences in these physiological parameters indicate greater prevention of water loss in Tiber during drought, which may be associated with rapid and adequate down-regulation of aquaporins. These results suggest that the ability of plants to conserve water during drought stress involves timely and sufficient down-regulation of gene expression of specific aquaporins.     

Response of chlorophyll fluorescence parameters to drought stress in sugar beet seedlings

We compared the parameters of chlorophyll fluorescence between two sugar beet (Beta vulgaris L.) species differing in drought tolerance. Our results indicated that there were different responses to the drought stress of these sugar beet species. In drought-tolerant sugar beet, the F ₀ increased slightly, while qN increased substantially, indicating that these plants can protect PSII reaction centers from the damage. F _v/F _m and qP decreased slightly during the initial period of drought stress; this suggests that there is a slight impact of drought stress on the openness of PSII reaction centers, and thus the plants did not suffer seriously. This was further shown by the decreased Yield and electron transfer rate. The parameters of chlorophyll fluorescence were stable and can be used as an important indicator for sugar beet seedlings in the early drought tolerance.     

水分胁迫对不同抗旱类型冬小麦幼苗叶绿素荧光参数的影响

在人工气候室水培条件下,选用3个不同抗旱类型的冬小麦品种,研究了水分胁迫对冬小麦幼苗叶绿素荧光参数的影响。结果表明：水分胁迫下,冬小麦幼苗可变荧光(Fv)、最大荧光(Fm)、可变荧光与最大荧光比(Fv／Fm)、可变荧光与初始荧光比(Fv／Fo)、光化学淬灭系数(qF)均降低;而初始荧光(Fo)与非光化学淬灭系数(qNP)则升高,说明光系统Ⅱ(PSⅡ)受到了伤害,使得PSⅡ原初光能转换效率(Fv／Fm)、PSⅡ潜在活性(Fv／Fo)降低;光合电子传递、光合原初反应过程受到抑制,起光保护作用的热耗散提高。但水分胁迫下品种间各参数变化幅度不同。除qNF外,其余各参数均为抗旱性越强降低幅度越小,而qNF则升高幅度越大。说明水分胁迫对冬小麦幼苗叶绿素荧光参数的影响与其抗旱性密切相关。     

Gas exchange,chlorophyll fluorescence,and osmotic adjustment in two mango cultivars under drought stress

The responses of photosynthetic gas exchange, chlorophyll fluorescence, content of pigments, main osmolytes, and malondialdehyde (MDA) to water-withholding for 15 days and re-hydration in seedlings of two mango cultivars (Mangifera indica L. var. “Choke Anand’ and var. “Khieo Sawoei”) under 50% sunlight and full sunlight were investigated. For both cultivars, the water-witholding resulted in progressively decreases in leaf relative water content, net photosynthesis (P _n), stomatal conductance (g _s), and increases in the conversion of xanthophyll cycle pigments estimated by an index of leaf spectral reflectance (ΔPRI), carotenoid to chlorophyll ratio, non-photochemical quenching (NPQ), the contents of malondialdehyde (MDA) and compatible solutes (total soluble sugar and proline). The effect of the water stress was more pronounced in full sunlight than 50% sunlight. The maximum photochemistry efficiency measured at dawn was fairly constant during the period of the treatment for both cultivars under both light regimes. The water stress caused less pronounced inhibition of photosynthesis in “Choke Anand” than in “Khieo Sawoei” cultivar under both light regimes. After re-hydration, the recovery was relatively quicker in “Choke Anand” than in “Khieo Sawoei” cultivar. Both cultivars in both 50% and full sunlight showed complete recovery in photochemistry after 5 days of re-watering but photosynthesis did not show a complete recovery as indicated by gas exchange rates. As the results of lower NPQ, ΔPRI and osmotic adjustment in the cultivar “Khieo Sawoei” compared to the cultivar “Choke Anand”, the former cultivar was less tolerant to drought than the latter. Our study further showed that partial shading (e.g., 50% of sunlight) significantly alleviated the harmful effect of drought stress on mango cultivars but in fact stomata of seedlings grown in partial shade was more responsive to water deficit than in full light.     

Differential responses of antioxidant system and photosynthetic characteristics in four rice cultivars differing in sensitivity to sodium chloride stress

To keep pace with ever growing global population, progressive and sustained increase in rice production is necessary, especially in areas with extremely variable climatic conditions, where rice crop suffers from numerous abiotic stresses including salinity. Designing an effective phenotyping strategy requires thorough understanding of plant survival under stress. The investigation was carried out with four rice cultivars namely FR13A, IR42, Rashpanjor, and Pokkali that differed in salinity tolerance. The study showed that a genotype with initial vigour had some advantage in preserving shoot biomass under salt stress. Though both FR13A and IR42 showed sensitivity to salinity, FR13A with higher initial biomass maintained greater dry weight under saline condition. Increase of Na⁺:K⁺ ratio under salinity, due to accelerated absorption of Na⁺ and lesser absorption of K⁺ compared to control, was considerably higher in susceptible (118–200 %) than in tolerant (33–48 %) genotypes. While Na⁺ concentration in shoot increased significantly in both tolerant and susceptible genotypes, decrease in shoot K⁺ content was noticed only in susceptible genotypes. The imbalance of Na⁺ and K⁺ contents led to increased H₂O₂ production, causing greater peroxidation of membrane lipids and reduction in chlorophyll content and CO₂ photosynthetic rate. Certain chlorophyll fluorescence parameters could distinguish between salinity tolerant and sensitive genotypes. To protect the plant from oxidative damage, several enzymatic and nonenzymatic antioxidants such as ascorbate were involved. The genotypes with capacity to assemble antioxidant enzymes in time could detoxify the reactive oxygen species more efficiently, leading to greater protection and reduced impact of salt stress.     

Expression profiling of rice cultivars differing in their tolerance to long-term drought stress

Understanding the molecular basis of plant performance under water-limiting conditions will help to breed crop plants with a lower water demand. We investigated the physiological and gene expression response of drought-tolerant (IR57311 and LC-93-4) and drought-sensitive (Nipponbare and Taipei 309) rice (Oryza sativa L.) cultivars to 18 days of drought stress in climate chamber experiments. Drought stressed plants grew significantly slower than the controls. Gene expression profiles were measured in leaf samples with the 20 K NSF oligonucleotide microarray. A linear model was fitted to the data to identify genes that were significantly regulated under drought stress. In all drought stressed cultivars, 245 genes were significantly repressed and 413 genes induced. Genes differing in their expression pattern under drought stress between tolerant and sensitive cultivars were identified by the genotype x environment (G x E) interaction term. More genes were significantly drought regulated in the sensitive than in the tolerant cultivars. Localizing all expressed genes on the rice genome map, we checked which genes with a significant G x E interaction co-localized with published quantitative trait loci regions for drought tolerance. These genes are more likely to be important for drought tolerance in an agricultural environment. To identify the metabolic processes with a significant G x E effect, we adapted the analysis software MapMan for rice. We found a drought stress induced shift toward senescence related degradation processes that was more pronounced in the sensitive than in the tolerant cultivars. In spite of higher growth rates and water use, more photosynthesis related genes were down-regulated in the tolerant than in the sensitive cultivars.     

The effect of drought stress on chlorophyll fluorescence in Lolium-Festuca hybrids

The effects of drought on photochemical efficiency of PSII in leaves of 22 hybrids of Festuca pratensis × Lolium multiflorum and Festuca pratensis × Lolium perenne and of Festuca pratensis cv. Skra were investigated. A significant decrease of electron transport efficiency (about 25%) in PSII (Φ_PSII) was not found before 9 days of seedling growth in hydroponics with water potential (Ψ_w) equal to −0.8 MPa (simulated “soil drought”). The decrease of Φ_PSII was similarly related to that of excitation energy capture by open PSII reaction centre (Fv’/Fm’) and also to the decrease of the proportion of oxidized to reduced Q_A (photochemical fluorescence quenching, q_p). According to the drought prolongation, variation of all parameters of fluorescence between genotypes significantly increased. The seedlings of some genotypes were able to recover electron transport efficiency in PSII after increasing water potential in nutrient solution (removing the “soil drought”). When plants grew in containers with soil and 4 genotypes with the highest sensitivity of electron transport to drought (S) as well as 4 genotypes with the highest tolerance (T) were compared 17 days after watering ceased, Ψ_w in leaves considerably decreased, but the differences between S and T genotypes were often not significant in this respect. The differences between S and T genotypes, as values of Fv/Fm were concerned, also appeared small (about 5%), similarly as that of Fv’/Fm’ (5%), q_p (12%) and Φ_PSII (about 15%). Drought stress increased non-photochemical quenching of chlorophyll fluorescence (NPQ) 15 to 47% and this could protect the PSII reaction centres from damages because of energy excess. The increase of NPQ was not closely connected with drought resistance of plants because it was similar in some genotypes tolerant to dehydration as well as in sensitive ones. The results of the experiments suggest that resources of genetic variability in Festulolium may be sufficient for revealing differences between genotypes on the basis of measurement of chlorophyll a fluorescence, as far as their tolerance to soil drought is concerned. As the tolerance of PSII against drought is high, the determinations of fluorescence should be performed rather under severe stress. Such methods seem to be useful for selection of genotypes with high drought tolerance as well as with the ability to at least partial repairing of PSII after drought.     

干旱胁迫下黄条金刚竹的光合和叶绿素荧光特性

通过盆栽试验,研究了自然干旱胁迫处理下,黄条金刚竹植株形态、土壤含水量(SWC)、叶片含水量(LWC)、叶片水势(LWP)、光合作用参数和叶绿素荧光参数的变化,及与环境因素的关系.结果表明:自然干旱胁迫后第17天,黄条金刚竹出现干旱伤害症状,叶片失水下垂、内卷,第43天地上部分失水死亡;复水后10 d,叶片叶绿素荧光参数与第43天无显著差异.在干旱胁迫0～21 d,SWC显著下降,而在17 d以后,LWP急剧下降,29 d以后LWC显著降低.随着干旱胁迫程度的加剧,叶片蒸腾速率(T_r)、气孔导度(g_s)持续下降,而光合速率(P_n)波动较大,瞬时水分利用效率（PWUE）则先升高后降低;17 d后,P_n由气孔限制为主转为非气孔限制为主,实际光合效率(Φ_PSⅡ)开始下降;25 d后,黄条金刚竹的光合机构被破坏,最大光化学效率(F_v/F_m)和PSⅡ潜在热耗散能力(q_N)分别由0.64、0.79下降到-0.11、0.33.T_r、g_s、PWUE与LWP密切相关,大气湿度对P_n、T_r、g_s的影响显著,气孔是光合参数变化的主导因素.本试验条件下,黄条金刚竹适宜在土壤相对含水率≥12%的土壤中生长,且干旱胁迫持续时间不超过25 d.     

Responses of antioxidative system to chilling stress in two rice cultivars differing in sensitivity

The responses of antioxidative system of rice to chilling were investigated in a tolerant cultivar, Xiangnuo-1, and a susceptible cultivar, IR-50. The electrolyte leakage and malondialdehyde content of Xiangnuo-1 were little affected by chilling treatment but those of IR-50 increased. Activities of suoperoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase, and ascorbic acid content of Xiangnuo-1 were remained high, while those of IR-50 decreased under chilling. The results indicated that higher activities of defense enzymes and higher content of antioxidant under stress were associated with tolerance to chilling.     

Relationship between carbohydrate partitioning and drought resistance in common bean

Drought is a major yield constraint in common bean (Phaseolus vulgaris L.). Pulse-chase (14)C-labelling experiments were performed using Pinto Villa (drought resistant) and Canario 60 (drought sensitive) cultivars, grown under optimal irrigation and water-deficit conditions. Starch and the radioactive label incorporated into starch were measured in leaves and pods at different time points, between the initiation of pod development and the production of mature pods. The water-stress treatment induced a higher starch accumulation in the drought-resistant cultivar pods than in those of the drought-sensitive cultivar. This effect was more noticeable during the early stages of pod development. Consistently, a reduction of starch content occurred in the leaves of the drought-resistant cultivar during the grain-filling stage. Furthermore, a synchronized accumulation of sucrose was observed in immature pods of this cultivar. These data indicate that carbohydrate partitioning is affected by drought in common bean, and that the modulation of this partitioning towards seed filling has been a successful strategy in the development of drought-resistant cultivars. In addition, our results suggest that, in the drought-resistant cultivar, the efficient carbon mobilization towards the seeds in response to water limitation is favoured by a mechanism that implies a more effective sucrose transport.     

The accumulation of trehalose in nodules of several cultivars of common bean (Phaseolus vulgaris) and its correlation with resistance to drought stress

Nine cultivars of common bean were grown in the presence of a natural microflora without exogenous rhizobial inoculation. Nodules were harvested 30 days post planting (early flowering stage) and the presence of trehalose determined. Amounts present varied according to cultivar and were between 0.20 and 1.63 mg g⁻¹ nodule dry weight. Rhizobial strains were isolated from the nodules of three selected cultivars (Canario 101, Flor de Mayo Bajio and Flor de Mayo 38). Trehalose levels in nodules produced after either mixed strain reinfection, or after axenic homologous reinfection or after axenic cross‐reinfection could be manipulated by applying drought stress. Mixed reinfection nodules from stressed plants accumulated between two and six times the trehalose concentration found in non‐stressed control plants. After axenic cross‐reinfection up to 48‐fold increases in nodule trehalose content were recorded during drought stress. Those cultivars exhibiting high nodule trehalose levels and/or a high degree of trehalose stimulation in response to drought stress also exhibited a high leaf relative water content and were also the most drought resistant. During drought stress nodule trehalase levels rose only slightly.     

Electrolyte leakage and chlorophyll a fluorescence among castor bean cultivars under induced water deficit

We evaluated leaf fragments of three castor bean cultivars after being subjected to water stress. Leaf discs were exposed to polyethylene glycol (PEG-6000) solutions for tissue dehydration at various water potentials. After water-stress imposition, electrolyte leakage and chlorophyll a fluorescence were used jointly on the same leaf fragments cut from the same plant leaf. Furthermore, these two experimental procedures were adapted to unequivocally distinguish cultivars’ responses to water stress. Electrolyte leakage, ion efflux, membrane injury index and maximum quantum yield of photosystem II showed genotypic differences between cultivars. Despite these genotypic differences, the photosystem II electron transport rate was not significantly affected by water stress. The membrane injury shown may have been transient, probably due to a disarrangement in the phospholipid bilayer. The use of the two experimental procedures on the same leaf samples was less time-consuming and allowed for more reliable results. Furthermore, the procedures proved efficient for selection of physiological water-stress tolerance traits and could be employed in other plant experimental models.     

5-Aminolevulinic acid enhances photosynthetic gas exchange, chlorophyll fluorescence and antioxidant system in oilseed rape under drought stress

This study evaluates the role of exogenous foliar application of 5-aminolevulinic acid (ALA) on water relations, gas exchange, chlorophyll fluorescence, and the activities and gene expression patterns of antioxidant enzymes in leaves of oilseed rape under drought stress and recovery conditions. Seedlings at four-leaf stage were imposed to well-watered condition (80 % of water-holding capacity) or drought stress (40 % of water-holding capacity) and subsequently foliar sprayed with water or ALA (30 mg l^?1). Drought suppressed the accumulation of plant biomass and decreased chlorophyll content and leaf water status (relative water content and water potential). The actual quantum yield of photosystem II and electron transport rates were hampered in parallel to net photosynthetic rate. However, drought stress induced the accumulation of malondialdehyde (MDA) and hydrogen peroxide, enhanced the activities of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) and superoxide dismutase and up-regulated the expression of APX and GR. After rehydration for 4 days, the growth of drought-treated seedlings was restored to normal level for most of the physiological parameters. Foliar application of ALA maintained relatively higher leaf water status and enhanced chlorophyll content, net photosynthetic rate, actual quantum yield of photosystem II, photochemical quenching, non-photochemical quenching and electron transport rates in stressed leaves. Exogenous ALA also alleviated the accumulation of MDA and hydrogen peroxide, increased the activities of antioxidant enzymes and enhanced the expression of CAT and POD in drought-treated plants. These results indicate that ALA may effectively protect rapeseed seedlings from damage induced by drought stress.     

Changes in chlorophyll fluorescence parameters and oxidative stress responses of bush bean genotypes for selecting contrasting acclimation strategies under water stress

Drought resistance of bean landraces was compared in order to select genotypes with either high morphological or high biochemical-physiological plasticity. The lines in the former group exhibited fast reduction in fresh and dry mass, decreased the water potential in primary leaves after irrigation withdrawal and the biomass mobilized from the senescent primary leaves was allocated into the roots. These genotypes had high frequency of primary leaf abscission under water stress. The genotypes with plasticity at the biochemical level maintained high water potential and photochemical efficiency, i.e. effective quantum yield, high photochemical (qP) and low non-photochemical (NPQ) quenching in primary leaves under drought stress. While superoxide dismutase activity was not influenced by the drought and the genotype, catalase activity increased significantly in the primary leaves of the genotypes with efficient biochemical adaptation. Lines with high morphological plasticity exhibited higher quaiacol peroxidase activity under drought. Proline may accumulate in both cases, thus it may be a symptom of protein degradation or a successful osmotic adaptation. On the basis of contrasting responses, the genetic material cannot be screened for a large-scale breeding program by a single physiological parameter but by a set of the methods presented in this work.     

Differences in growth and water relations among Phaseolus vulgaris cultivars in response to induced drought stress

Relatively little ecophysiological research has been conducted to determine the responses to drought of Phaseolus vulgaris. Four bean cultivars (cvs.) from Brazil, A320, Carioca, Ouro Negro and Xodó were submitted to an imposed water deficit in order to evaluate the importance of some adaptive mechanisms of drought resistance through the analysis of growth parameters, water status, gas exchange and indicators of tolerance mechanisms at the cellular level. During the drought treatment, relative growth rates were more reduced for A320 and Xodó than Carioca and Ouro Negro. A320 closed its stomata very rapidly and complete stomatal closure was obtained at Psi(w)=-0.6 MPa, in contrast to the other cvs. where stomata were fully closed only at Psi(w)=-0.9 MPa. Net assimilation rates were closely related to stomatal conductances. Mechanisms at the cellular level appeared to be mostly important for higher tolerance. Carioca and Ouro Negro, when compared to A320 and Xodó, were characterized by having better drought tolerance mechanisms and higher tissue water retention capacity leading to a better growth under water deficits. The leaf dehydration rates of those cvs. were slow whereas those of the drought sensitive cvs. were rapid. The results were confirmed by the electrolyte leakage test and leaf osmotic potential measurements, which indicated higher membrane resistance and osmotic adjustment in the two tolerant cvs. Carioca and Ouro Negro. It appears from this study that despite being cultivated in the same geographical region, the four cvs. of P. vulgaris displayed somewhat different drought adaptive capacities for prolonged drought during the vegetative phase.     

Growth and cell wall properties of two wheat cultivars differing in their sensitivity to aluminum stress

The present study was conducted to investigate the cell wall properties in two wheat (Triticum aestivum L.) cultivars differing in their sensitivity to Al stress. Seedlings of Al-resistant, Inia66 and Al-sensitive, Kalyansona cultivars were grown in complete nutrient solutions for 4 days and then subjected to treatment solutions containing Al (0, 50 microM) in a 0.5 mM CaCl(2) solution at pH 4.5 for 24 h. Root elongation was inhibited greatly by the Al treatment in the Al-sensitive cultivar compared to the Al-resistant cultivar. The Al-resistant cultivar accumulated less amount of Al in the root apex than in the Al-sensitive cultivar. The contents of pectin and hemicellulose in roots were increased with Al stress, and this increase was more conspicuous in the Al-sensitive cultivar. The molecular mass of hemicellulosic polysaccharides was increased by the Al treatment in the Al-sensitive cultivar. The increase in the content of hemicellulose was attributed to increase in the contents of glucose, arabinose and xylose in neutral sugars. Aluminum treatment increased the contents of ferulic acid and p-coumaric acid especially in the Al-sensitive cultivar by increasing the activity of phenylalanine ammonia lyase (PAL, EC 4.3.1.5). Aluminum treatment markedly decreased the beta-glucanase activity in the Al-sensitive cultivar, but did not exert any effect in the Al-resistant cultivar. These results suggest that the modulation of the activity of beta-glucanase with Al stress may be involved in part in the alteration of the molecular mass of hemicellulosic polysaccharides in the Al-sensitive cultivar. The increase in the molecular mass of hemicellulosic polysaccharides and ferulic acid synthesis in the Al-sensitive cultivar with Al stress may induce the mechanical rigidity of the cell wall and inhibit the elongation of wheat roots.     

Influence of water stress on leaf photosynthetic characteristics in wheat cultivars differing in their susceptibility to drought

A gradual reduction in leaf water potential (Ψ_leaf), net photosynthetic rate (P _N), stomatal conductance, and transpiration rate was observed in two drought tolerant (C 306 and K 8027) and two susceptible (RW 893 and 899) genotypes subjected to water stress. The extent of reduction was lower in K 8027 and C 306 and higher in RW 893 and RW 899. Rewatering the plants after 5 d of stress restored P _N and other gas exchange traits in all four cultivars. Water stress had no significant effect on variable to maximum fluorescence ratio (F_v/F_m) indicating that water stress had no effect on primary photochemistry of photosystem 2 (PS2). However, water stress reduced the efficiency of excitation energy transfer (F′_v/F′_m) and the quantum yield of electron transport (Φ_PS2). The reduction was more pronounced in susceptible cultivars. Water stress had no significant effect on photochemical quenching, however, the non-photochemical quenching increased by water stress.     

不同干旱胁迫条件下丛枝菌根真菌对 木棉叶绿素荧光参数的影响

为了探明丛枝菌根真菌(AMF)与木棉(Bombax ceiba Linn.)抗旱性的关系,采用盆栽法对不同干旱胁迫条件下接菌组(1 g土壤含100个AMF孢子)和未接菌组木棉叶绿素荧光参数进行了比较分析.结果表明:中度干旱胁迫(土壤相对含水量45%~50%)和重度干旱胁迫(土壤相对含水量30%~35%)条件下接菌组的初始荧光(Fo)均低于未接菌组;与对照(土壤相对含水量65%~70%)相比,重度干旱胁迫5、15和35 d,接菌组的Fo值分别升高了10.39%、20.93%和14.14%,未接菌组的Fo值分别升高了26.95%、48.75%和71.35%.接菌组的PSⅡ最大光化学效率(Fv/Fm)和PSⅡ潜在活性(Fv/Fo)在中度和重度干旱胁迫5、15和35 d均高于未接菌组.与对照相比,重度干旱胁迫5、15和35 d,接菌组的Fv/Fm值分别降低了9.09%、6.85%和22.06%,未接菌组的Fv/Fm值分别降低了10.67%、16.21%和52.78%;接菌组的Fv/Fo值分别降低了28.14%、22.43%和46.01%,未接菌组的Fv/Fo值分别降低了28.38%、48.20%和75.96%.总体来看,在中度和重度干旱胁迫条件下,接菌组的PSⅡ实际光量子产量〔Y(Ⅱ)〕、PSⅡ非调节性能量耗散的量子产量〔Y(NO)〕、光化学淬灭系数(qP)和光合电子传递速率(ETR)高于对照,而PSⅡ调节性能量耗散的量子产量〔Y(NPQ)〕和非光化学淬灭系数(qN)低于对照;未接菌组的Y(Ⅱ)、qP、qN和ETR值低于对照,而Y(NO)和Y(NPQ)值则高于对照.研究结果显示:AMF能够减轻干旱尤其是重度干旱胁迫条件下木棉受伤害和光抑制的程度,并提高其叶片PSⅡ反应中心的活性,从而增强木棉在干旱胁迫条件下的生存能力.     

Stability and anatomical parameters of irradiated potato cultivars under drought stress

This study was carried out in Desert Research Center and Faculty of Agriculture, Zagazig University, Egypt, under North Sinai conditions during three growing seasons, i.e., summer 2018, fall 2018/2019 and summer 2019 to assess the effect of radiation mutants on leaf histological features and genetic stability of the productivity of some potato cultivars under drought stress conditions. Results reveal that the genotypes can be statistically classified based on regression coefficient (bi), deviation from regression (S²di) to 4 groups (with low in S²di are considered in all groups) as: (i) Genotype with elevated average, bi = 1, it is considered as stable genotype where Cara cultivar (both generations) was included. (ii) Genotype with elevated average, bi > 1 as genotype with average stability where spunta cultivar was involved. (iii) Genotype with low mean, bi < 1 as genotype with low stability where hermes (both primary (M₁) and secondary (M₂) radiated generations) and Caruso (2nd generation) cultivars were involved. (iv) Genotypes including a few bi values in one generation, as genotype including low stability but are not recommended for use in this generation where Caruso cv in M₁ was included. The results indicated that 20 Gy irradiation exposure revealed that Spunta cultivar produced markedly high mean combined over yield during M₁ (11.771 ton/fed) and M₂ (10.97 ton/fed) generations than other genotypes and ranked first over all environments. It proves that Hermes could be employed as anti-stress genotypes under stress conditions (negative conditions or poor yielding). However, spunta followed by cara cv. represented a good performance in M₂ production yield (10.97 and 8.51 ton/fed, respectively), slight drift from the regression line and coefficient close to 1, therefore, both cultivars were excellent between genotypes in shape of yield stability and is recommended for different conditions. According to anatomical studies, 80 % from field capacity (FC) decreased the thickness of medvein and lamina of potato cv. spunta, also, dimensions of medvein bundle and mean diameter of vessels. In conclusion, plants treated with gamma ray at level 20 and grown under 80 % FC induced prominent increase in all previous characters.     

Changes in photosynthesis, chlorophyll fluorescence, and antioxidant enzymes of mulberry (Morus ssp.) in response to salinity and high-temperature stress

Photosynthesis, chlorophyll (Chl) fluorescence, and antioxidant enzymes were measured in the mulberry (Morus spp.) cultivars Da 10, Hongguo 2, Anza 1, and Taiwan 72C002, which were subjected to salinity and high-temperature stress (STS; 0.1%, 0.3%, and 0.5% NaCl concentrations, 34.5°C–40.5°C/27.8°C–29.2°C day/night temperatures). Control plants were watered with 1 L of full-strength Hoagland’s nutrient solution with no added NaCl. Net photosynthetic rate (P _N), stomatal conductance (g _s), and effective quantum yield of photosystem II photochemistry (Φ_PSII) increased in Anza 1 and Taiwan 72C002 under 0.1% STS but decreased in Da 10 and Hongguo 2 compared with the control. However, all the above parameters, including Chl content, maximum quantum yield of photosystem II photochemistry (F_v/F_m), nonphotochemical quenching (NPQ), and maximum carboxylation velocity of Rubisco (V _cmax, decreased in Taiwan 72C002, Honggua 2, and Da 10 under 0.3% and 0.5% STS, suggesting that photoinhibition occurred under severe STS. Under STS, there were no significant changes in P _N, F_v/F_m, Φ_PSII, ascorbate peroxidase (APX) activity, superoxide dismutase (SOD) activity, catalase activity, superoxide anion radical (O ₂ ^? ) content, malondialdehyde (MDA) content, soluble sugar content (SSC), and leaf biomass in Anza 1 even at 0.5% STS, showing that Anza 1 displays high resistance to STS. In addition, peroxidase activity was significantly higher in Anza 1 than in the other mulberry cultivars. Significant adverse effects of severe salinity on photosynthesis and Chl fluorescence parameters were observed in Da 10. Additionally, SOD, peroxidase, and APX activities were lower in Da 10, whereas O ₂ ^? and MDA contents were higher in comparison with the other mulberry cultivars under 0.3% and 0.5% STS, suggesting that Da 10 had low resistance to STS. These results show that 0.1% STS had a positive effect on photosynthesis and Chl fluorescence parameters in Anza 1 and Taiwan 72C002, and higher peroxidase activity can to a certain extent explain the higher STS tolerance in Anza 1. Damages to DSM photosystems might be related to lower SOD, POD, and APX activities, which resulted in the accumulation of reactive oxygen species.