外源脯氨酸对盐胁迫下甜瓜幼苗硝酸还原的影响

采用营养液水培方法,以＂雪美＂品种甜瓜（Cucumis melo L.）为材料,研究了外源脯氨酸（Proline）对盐胁迫下甜瓜幼苗叶片和根系硝酸还原的影响。结果表明：（1）盐胁迫提高了甜瓜幼苗叶片和根系内铵态氮（NH4＋-N）和可溶性蛋白含量;降低了硝态氮（NO-3-N）含量和硝酸还原酶（nitrate reductase,NR）活性。（2）外源施用脯氨酸明显地提高了盐胁迫下甜瓜幼苗叶片和根系内NO-3-N和可溶性蛋白含量;降低了盐胁迫下甜瓜幼苗叶片和根系内NH＋4-N含量;增强了盐胁迫下甜瓜幼苗体内NR活性。研究结果表明,外源脯氨酸可以通过调节甜瓜幼苗体内硝酸还原酶活性和氮化合物含量来缓解盐胁迫对甜瓜幼苗植株的伤害。     

A barley mutant with improved salt tolerance through ion homeostasis and ROS scavenging under salt stress

To investigate key regulatory components and genes with great impact on salt tolerance, near isogenic or mutant lines with distinct salinity tolerance are suitable genetic materials to simplify and dissect the complex genes networks. In this study, we evaluated responses of a barley mutant genotype (73-M4-30), in comparison with its wild-type background (Zarjou) under salt stress. Although the root growth of both genotypes was significantly decreased by exposure to sodium chloride (NaCl), the effect was greater in the wild type. The chlorophyll content decreased under salt stress for the wild type, but no change occurred in the mutant. The mutant maintained the steady-state level of [K⁺] and significantly lower [Na⁺] concentrations in roots and higher [K⁺]/[Na⁺] ratio in shoots under salt conditions. The catalase (CAT), peroxidase (POD) activity, and proline content were higher in the mutant than those in the wild type under controlled conditions. The soluble proline was higher after 24 h of salt stress in roots of the mutant but was higher after 96 h of salt stress in the wild type. The CAT and POD activity of the mutant increased under salt stress which was as a coincidence to lower levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents. The ratio of dry-to-fresh weight of the roots increased for the mutant under salt stress which was as a result of the higher phenylalanine ammonia-lyase (PAL) gene expression and peroxidase activity and involved in cell wall lignification. Consequently, it seems that ion homeostasis and increased peroxidase activity have led to salt tolerance in the mutant’s genotype.     

Exogenous proline mitigates the detrimental effects of salt stress more than exogenous betaine by increasing antioxidant enzyme activities

Proline and betaine accumulate in plant cells under environmental stresses including salt stress. Here, we investigated effects of proline and betaine on the growth and activities of antioxidant enzymes in tobacco Bright Yellow-2 (BY-2) culture cells in suspension under salt stress. Both proline and betaine mitigated the inhibition of growth of BY-2 cells under salt stress and the mitigating effect of proline was more than that of betaine. Salt stress significantly decreased the activities of superoxide dismutase (SOD), catalase and peroxidase in BY-2 cells. Exogenous application of proline or betaine alleviated the reduction in catalase and peroxidase activities but not SOD activity under salt stress. In addition, proline was found to be effective in alleviating the inhibition of salt stress-induced catalase and peroxidase activities in BY-2 cells. Neither proline nor betaine directly scavenged superoxide (O(2)(-)) or hydrogen peroxide (H(2)O(2)). It is concluded that exogenous proline mitigates the detrimental effects of salt stress more than exogenous betaine because of its superior ability to increase the activities of antioxidant enzymes.     

Comparative morphological and anatomical characters of Cakile arabica from different habitat in eastern region of Saudi Arabia

Morphological, anatomical and physiological plasticity was examined for Cakile arabica from three different sites at the coastal part of the Arabian Gulf near Ad Dammam city in the eastern region of Saudi Arabia. Morphological investigation showed that the size and number of lobes of the leaves are increased in sites (I) which have high salt stress. Also anatomical investigation using a light microscope showed that the plant is adaptive for salt stress by increasing the thickening of the cuticle or epidermis layer and increase in the area of vascular bundles. Physiological studies showed that plant growing under high salt stress is characterized by increase content of electrical conductivity and increase in chlorophyll a, b, carotenoids and proline content in the plant tissues. This can be explained as an osmotic adjustment mechanism for the investigated species growing under high salinity stress.     

Apoptosis-Like Cell Death in Barley Roots under Salt Stress

Salt stress-induced cell death was investigated in barley roots.Cleavage of nuclear DNA was observed 1 h after salt stress.Oligonucleosomal fragments of DNA were detected electrophoretically8 h after salt stress. These phenomena indicate that apoptosis-likecell death can occur under salt stress. (Received February 12, 1997; Accepted July 3, 1997)     

Salinity-induced changes in two cultivars of Vigna radiata: responses of antioxidative and proline metabolism

The influence of increasing salinity stress on plant growth, antioxidant enzymes and proline metabolism in two cultivars of Vigna radiata L. (cv. Pusa Bold and cv. CO 4) was investigated. Salt stress was imposed on 30-days-old cultivars with four different concentrations of NaCl (0, 100, 200 and 300 mM). The roots and shoots of CO 4 showed greater reduction in fresh weight, dry weight and water content when compared to Pusa Bold with increasing salt stress. Under salinity stress, the roots and shoots of CO 4 exhibited higher Na⁺: K⁺ ratio than Pusa Bold. The activities of reactive oxygen species (ROS) scavenging enzymes and reduced glutathione (GSH) concentration were found to be higher in the leaves of Pusa Bold than in CO 4, whereas oxidized glutathione (GSSG) concentration was found to be higher in the leaves of CO 4 compared to those in Pusa Bold. Our studies on oxidative damage in two Vigna cultivars showed lower levels of lipid peroxidation and H₂O₂ concentration in Pusa Bold than in CO 4 under salt stress conditions. High accumulation of proline and glycine betaine under salt stress was also observed in Pusa Bold when compared to CO 4. The activities of proline biosynthetic enzymes were significantly high in Pusa Bold. However, under salinity stress, Pusa Bold showed a greater decline in proline dehydrogenase (ProDH) activity compared to CO 4. Our data in this investigation demonstrate that oxidative stress plays a major role in salt-stressed Vigna cultivars and Pusa Bold has efficient antioxidative characteristics which could provide better protection against oxidative damage in leaves under salt-stressed conditions.     

外源脯氨酸对盐胁迫下甜瓜幼苗根系抗坏血酸-谷胱甘肽循环的影响

以2个不同耐盐强度的甜瓜品种‘玉皇’（耐盐性强）和‘雪美’（耐盐性弱）为材料,采用营养液栽培方法,研究外源脯氨酸对盐胁迫下甜瓜幼苗根系抗坏血酸-谷胱甘肽循环的影响。结果显示：（1）盐胁迫下,2个甜瓜品种根系内的还原型抗坏血酸（ASA）、还原型谷胱甘肽（GSH）含量降低,氧化型谷胱甘肽（GSSG）含量升高,且‘雪美’变化幅度大于‘玉皇’;（2）盐胁迫下,施用外源脯氨酸提高了2个甜瓜品种根系中ASA和GSH的含量,降低了GSSG含量,同时也提高了GSH/GSSG的比值,且对‘雪美’的作用大于‘玉皇’;（3）盐胁迫处理3 d时,2个甜瓜品种根系的抗坏血酸过氧化物酶（APX）、脱氢抗坏血酸还原酶（DHAR）、谷胱甘肽还原酶（GR）活性均下降,且‘雪美’下降的幅度较大;随着胁迫时间的延长（5 d时）,‘玉皇’幼苗根系内APX、DHAR、GR活性有所上升,‘雪美’根系中这3种酶活性则进一步降低;（4）盐胁迫下,施用外源脯氨酸提高了2个甜瓜品种根系内的APX、DHAR和GR的酶活性,且对‘雪美’的作用大于‘玉皇’。本研究结果表明,外源脯氨酸可以通过增加非酶促抗氧化物质ASA、GSH的含量和抗氧化酶活性,提高抗坏血酸-谷胱甘肽循环清除活性氧的能力,从而缓解盐胁迫对甜瓜植株的伤害。     

Time‐course analysis of salicylic acid effects on ROS regulation and antioxidant defense in roots of hulled and hulless barley under combined stress of drought,heat and salinity

Greater crop losses can result from simultaneous exposure to a combination of drought, heat and salinity in the field. Salicylic acid (SA), a phenolic phytohormone, can affect a range of physiological and biochemical processes in plants and significantly impacts their resistance to these abiotic stresses. Despite numerous reports involving the positive effects of SA by applying each abiotic stress separately, the mechanism of SA‐mediated adaptation to combined stresses remains elusive. This study, via a time‐course analysis, investigated the role of SA on the roots of hulled and hulless (naked) barley (Hordeum vulgare L. ‘Tarm’ and ‘Özen’, respectively), which differed in salt tolerance, under the combined stress of drought, heat and salt. The combined stress caused marked reductions in root length and increases in proline content in both genotypes; however, Tarm exhibited better adaptation to the triple stress. Under the first 24 h of stress, superoxide dismutase (SOD; EC.1.15.1.1) and peroxidase (POX; EC.1.11.1.7) activity in the Tarm roots increased remarkably, while decreasing in the Özen roots. Furthermore, the Tarm roots showed higher catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) activity than the Özen during the combined stresses. The sensitivity of hulless barley roots may be related to decreasing SOD, POX, CAT and GR activity under stress. Over 72 h of stress, the SA pretreatment improved the APX and GR activity in Tarm and that of POX and CAT in Özen, demonstrating that exogenously applied SA regulates antioxidant defense enzymes in order to detoxify reactive oxygen species. The results of this study suggest that SA treatment may improve the triple‐stress combination tolerance in hulled and hulless barley cultivars by increasing the level of antioxidant enzyme activity and promoting the accumulation of proline. Thus, SA alleviated the damaging effects of the triple stress by improving the antioxidant system, although these effects differed depending on characteristic of the hull of the grain.     

盐胁迫下盐桦生理响应的变化分析

对组织培养获得的盐桦（Belula halophila）苗在盐胁迫下的生理指标和解剖结构进行了分析,结果显示,随着盐浓度的增加,植物叶片相对含水量逐渐降低;脯氨酸（Pro）含量逐渐增加;叶片丙二醛（MDA）含量和过氧化氢酶（CAT）活性大小存在相关性,在50～200mmol／L盐胁迫下,植物的CAT活性是递增的,200mmol／LNaCl处理时达到最高,同时叶片MDA含量在50～200mmol／L盐处理时变化不明显;CAT活性在300mmol／LNaCl处理时突然降低,此时叶片MDA含量大;植物叶片和根的离子含量测定表明,在盐胁迫下K^＋／Na^＋比值逐渐降低,叶片中K^＋含量始终高于Na^＋含量;石蜡切片和扫描电镜发现盐桦茎、叶中有晶体状物质存在,通过X-ray分析表明这种晶体含有C,O,Ca元素,相关的细胞成分化学实验进一步确定其结晶体的成分。     

The influence of salinity on cell ultrastructures and photosynthetic apparatus of barley genotypes differing in salt stress tolerance

A hydroponic experiment was conducted to elucidate the difference in growth and cell ultrastructure between Tibetan wild and cultivated barley genotypes under moderate (150 mM NaCl) and high (300 mM NaCl) salt stress. The growth of three barley genotypes was reduced significantly under salt stress, but the wild barley XZ16 (tolerant) was less affected relative to cultivated barley Yerong (moderate tolerant) and Gairdner (sensitive). Meanwhile, XZ16 had lower Na⁺ and higher K⁺ concentrations in leaves than other two genotypes. In terms of photosynthetic and chlorophyll fluorescence parameters, salt stress reduced maximal photochemical efficiency (F _v/F _m), net photosynthetic rate (Pn), stomatal conductance (Gs), and intracellular CO₂ concentration (Ci). XZ16 showed relatively smaller reduction in comparison with the two cultivated barley genotypes. The observation of transmission electron microscopy found that fundamental cell ultrastructure changes happened in both leaves and roots of all barley genotypes under salt NaCl stress, with chloroplasts being most changed. Moreover, obvious difference could be detected among the three genotypes in the damage of cell ultrastructure under salt stress, with XZ16 and Gairdner being least and most affected, respectively. It may be concluded that high salt tolerance in XZ16 is attributed to less Na⁺ accumulation and K⁺ reduction in leaves, more slight damage in cell ultrastructure, which in turn caused less influence on chloroplast function and photosynthesis.     

Compatible solute accumulation and stress-mitigating effects in barley genotypes contrasting in their salt tolerance

The accumulation of compatible solutes is often regarded as a basic strategy for the protection and survival of plants under abiotic stress conditions, including both salinity and oxidative stress. In this work, a possible causal link between the ability of contrasting barley genotypes to accumulate/synthesize compatible solutes and their salinity stress tolerance was investigated. The impact of H(2)O(2) (one of the components of salt stress) on K(+) flux (a measure of stress 'severity') and the mitigating effects of glycine betaine and proline on NaCl-induced K(+) efflux were found to be significantly higher in salt-sensitive barley genotypes. At the same time, a 2-fold higher accumulation of leaf and root proline and leaf glycine betaine was found in salt-sensitive cultivars. The total amino acid content was also less affected by salinity in salt-tolerant cultivars. In these, potassium was found to be the main contributor to cytoplasmic osmolality, while in salt-sensitive genotypes, glycine betaine and proline contributed substantially to cell osmolality, compensating for reduced cytosolic K(+). Significant negative correlations (r= -0.89 and -0.94) were observed between Na(+)-induced K(+) efflux (an indicator of salt tolerance) and leaf glycine betaine and proline. These results indicate that hyperaccumulation of known major compatible solutes in barley does not appear to play a major role in salt-tolerance, but rather, may be a symptom of salt-susceptibility.     

Does proline accumulated in leaves of water deficit stressed barley plants confine cell membrane injury? I. Free proline accumulation and membrane injury index in drought and osmotically stressed plants

The aim of this work was to examine the relationship between proline accumulation and membrane injury in barley leaves suffering from the effects of water deficit. Water deficit stress was induced by water withholding or by immersing the roots in polyethylene glycol (PEG 6000) solution of osmotic potential −1.5 MPa. The effect of water stress on proline accumulation and on membrane injury was evaluated in leaf blades of several barley genotypes. Substantial differences in proline accumulation and membrane injury indices among most of the genotypes investigated were observed. It was found that in drought stressed plants a higher ability to accumulate proline positively correlates with lower membrane injury. Whereas, in osmotically stressed plants the highest proline accumulation in the leaves was noticed in genotype with the largest membrane injury. The possible role of proline in membrane protection under conditions of slow-acting drought or shock-acting osmotic stress is discussed.     

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.     

盐胁迫下大麦根系木质部压力的自调节现象

用植物木质部压力探针测定的结果表明,水培大麦幼苗根的木质部压力在环境条件恒定不变时始终保持波动,并且在受到轻度的盐胁迫和当盐胁迫解除时表现出高度的自调节现象.这种波动和自调节现象将对植物水势的测定和根的径向反射系数的测定产生很大的影响,并可能与植物的抗盐性有关.小麦根在同样条件下未表现出上述现象.     

Free proline accumulation in cereals in relation to salt tolerance

In a micro-plot experiment it was observed that free proline accumulation in barley and wheat crops increased with the salt stress. But in sensitive strains of both the crops it did not accumulate in accordance with the preceding values after their tolerance limit and at this point yield of barley was reduced by 25.8% and wheat by 23.2% over control while significant yield reductions were not observed with tolerant strains. Proline accumulation was also found to be related to tissue K/Na ratio and the critical limits of this ratio were observed between 0.60 and 0.34 for barley and 4.2 and 1.4 for wheat.     

The physiological response of Artemisia annua L. to salt stress and salicylic acid treatment

Salinity has a great influence on plant growth and distribution. A few existing reports on Artemisia annua L. response to salinity are concentrated on plant growth and artemisinin content; the physiological response and salt damage mitigation are yet to be understood. In this study, the physiological response of varying salt stresses (50, 100, 200, 300, or 400 mM NaCl) on A. annua L. and the effect of exogenous salicylic acid (0.05 or 0.1 mM) at 300-mM salt stress were investigated. Plant growth, antioxidant enzyme activity, proline, and mineral element level were determined. In general, increasing salt concentration significantly reduced plant growth. Superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were stimulated by salt treatment to a higher enzyme activity in treated plants than those in untreated plants. Content of proline had a visible range of increment in the salt-treated plants. Distribution of mineral elements was in inconformity: Na⁺ and Ca²⁺ were mainly accumulated in the roots; K⁺ and Mg²⁺ were concentrated in leaves and stems, respectively. Alleviation of growth arrest was observed with exogenous applications of salicylic acid (SA) under salt stress conditions. The activity of SOD and POD was notably enhanced by SA, but the CAT action was suppressed. While exogenous SA had no discernible effect on proline content, it effectively inhibited excessive Na⁺ absorption and promoted Mg²⁺ absorption. Ca²⁺ and K⁺ contents showed a slight reduction when supplemented with SA. Overall, the positive effect of SA towards resistance to the salinity of A. annua will provide some practical basis for A. annua cultivation.