Effect of salt and water stress on RNA synthesis in the excised embryo axis of germinating mung bean (Phaseolus aureus ROXB).

The rate of synthesis of RNA was studied under salt and water stresses created by the addition of four different salts and polyethylene glycol-6000 (PEG-6000) in excised embryo axis of mung bean using^l4C-uracil. Iso-osmotio concentrations of salts and PEG resulted in differential effect on RNA synthesis. PEG inhibited, whereas salt stimulated incorporation of labelled uracil into RNA. Ionic differences on RNA synthesis were very clear as synthesis of RNA was more affected with sulphate than chloride and with sodium than potassium ions.     

Changes in water relations and in some physiological functions of bean under very light osmotic shock induced by polyethylene glycol

Bean plantlets ( Phaseolus vulgaris L. cv. Topcrop) were stressed at the age of 16–18 days by gradual (2–8%) or abrupt addition of 6% (w/v) polyethylene glycol Mw 6000 (PEG 6000) to Hoagland solution. Leaf conductance, photosynthesis, internal CO₂ partial pressure (C_i), relative water content (RWC), water content/dry weight (H₂O/DW), apoplastic PEG concentrations and weight of leaves, stems and roots were determined. Leaf conductance, photosynthesis and C_i were determined on non-detached primary leaves, and leaf potentials (water, osmotic and turgor potentials) were investigated in freshly detached (non-rehydrated) primary leaves, both in treated and control plants; RWC and osmotic potential were also assessed at the null turgor point. Low PEG 6000 concentrations induced early and evident decrease in leaf conductance and photosynthesis, whereas C_i decreased only moderately and tended to recover during advanced stress. There were moderate though significant decreases in RWC and H₂O/DW, no change or increases in water potential, no significant changes in osmotic potential and a moderate but significant increase in turgor potential. Even when referred to null turgor point, RWC significantly decreased and osmotic potential was unchanged. It was concluded that apoplastic PEG 6000 accumulation at evaporating sites would account for the early decrease in conductance which would also justify the unchanged or the prevalent increase in water potential and turgor potential. The subsequent PEG diffusion and concentration in the leaf apoplastic water would have induced the RWC and H₂O/DW decrease and the final turgor flexion documented.     

五唇兰对PEG模拟的干旱胁迫响应研究

为了解干旱对五唇兰(Phalaenopsis pulcherrima)生长的影响,以聚乙二醇(PEG)溶液模拟干旱胁迫,对其叶片的光合色素、渗透调节物质和非结构碳水化合物(NSC)含量变化进行研究。结果表明,随着PEG浓度增加,五唇兰植株含水量和鲜质量逐渐下降,以PEG为13.75%～14.84%时最显著。PEG处理显著降低叶片的叶绿素a和b含量。随着植株含水量的降低,叶片可溶性蛋白、淀粉(St)含量均呈下降趋势,可溶性糖(SS)含量、NSC和SS/St均呈先升后降的趋势。因此,干旱胁迫会影响五唇兰植株的含水量和光合产物的积累;在较低程度干旱胁迫下,可溶性糖在抗旱响应中发挥主要作用;随着干旱胁迫程度加深,五唇兰的生理代谢受到严重影响。     

PEG胁迫对文冠果种子萌发和幼苗生理特性的影响

在种子发芽箱中,以清水为对照,用5%、10%、15%、20%、25%、30%和35%共7个浓度聚乙二醇(PEG-6000)溶液浇灌栽培基质,观察文冠果种子的萌发和幼苗生长情况,以及幼苗叶片脯氨酸、丙二醛的含量和细胞膜相对透性的变化,探讨文冠果种子萌发对土壤水分的要求及其幼苗忍耐干旱的能力。结果显示:(1)在PEG浓度5%～35%范围内,文冠果种子发芽率、成苗率、幼苗根长和细胞膜透性均随着胁迫强度的增加呈明显的下降趋势;细胞膜透性随着胁迫强度的增加先升高后降低,但脯氨酸、丙二醛含量和幼苗根数量则呈现逐渐上升趋势。(2)5%的PEG浓度能够促进文冠果种子萌发,提高成苗率和根数量,降低幼苗死亡率;5%～10%的PEG能够明显促进苗高生长,但对根长影响不大;当PEG浓度高于15%后,种子萌发受到抑制,成苗率明显降低。(3)当PEG浓度高于25%时幼苗死亡率急剧上升,幼苗脯氨酸含量、丙二醛含量和细胞膜透性显著增加,细胞膜结构受到严重伤害。研究表明,低浓度PEG处理有利于文冠果种子萌发和幼苗生长,但过高浓度却对文冠果种子萌发和幼苗生长具有一定的抑制作用;文冠果种子萌发及其幼苗可忍受5%～25%的PEG渗透胁迫,即文冠果种子萌发和幼苗生长可忍受土壤水势为-7.94～-11.05MPa的干旱胁迫。     

Halopriming of seeds imparts tolerance to NaCl and PEG induced stress in Vigna radiata (L.) Wilczek varieties

The investigation was carried out to study the effect of halopriming on NaCl and polyethylene glycol-6000 (PEG-6000) induced stress tolerance potential of three Vigna radiata (L.) Wilczek varieties, with varied abiotic stress tolerance potential. Halopriming is a seed priming technique in which the seeds were soaked in various salt solutions (in this study NaCl was used). The results of the study indicated that the application of stresses (both NaCl and PEG) induced retardation of growth attributes (measured in terms of shoot length, fresh weight, dry weight) and decrease in physiological attributes like total chlorophyll content, metabolites, photosynthetic and mitochondrial activity of the seedlings in all three V. radiata (L.) varieties. However, halopriming of the seeds could reduce the extent of decrease in these biological attributes. NaCl and PEG stress also caused increase in MDA content (a product of membrane lipid peroxidation) in all the varieties studied and this increase was significantly minimized under halopriming. From the present investigation it was evident that among the green gram varieties studied, Pusa Vishal, a NaCl tolerant variety showed enhanced tolerance to NaCl and PEG induced stress, when the seeds were subjected to halopriming followed by Pusa Ratna (stress sensitive variety). Pusa 9531 (drought tolerant variety) also showed positive halopriming effects but it was less significant when compared to other two varieties. It could be concluded that halopriming improved the drought and salinity stress tolerance potential of all varieties and it was significantly higher in the Pusa Vishal as compared to Pusa 9531 and Pusa Ratna.     

Changes in content of free,conjugated and bound polyamines and osmotic adjustment in adaptation of vetiver grass to water deficit

Osmotic adjustment and alteration of polyamines (PAs) have been suggested to play roles in plant adaptation to water deficit/drought stress. In this study, the changes in cell intactness, photosynthesis, compatible solutes and PAs [including putrescine (Put), spermidine (Spd) and spermine (Spm) each in free, conjugated and bound forms] were investigated in leaves of vetiver grass exposed to different intensity of water deficit stress and subsequent rewatering. The results showed that, when vetiver grass was exposed to the moderate (20% and 40% PEG-6000 solutions) and severe (60% PEG solution) water deficit for 6 days, the plant injury degree (expressed as the parameters of plant growth, cell membrane integrity, water relations and photosynthesis) increased and contents of free and conjugated Put decreased with the rise of PEG concentration. Under the moderate water deficit, the plants could survive by the reduced osmotic potential (ψ_s), increased free and conjugated Spd and Spm in leaves. After subsequent rewatering, the osmotic balance was re-established, most of the above investigated physiological parameters were fully or partly recovered to the control levels. However, it was not the case for the severely-stressed and rewatering plants. It indicates that, vetiver grass can cope well with the moderate water deficit/drought stress by using the strategies of osmotic adjustment and maintenance of total contents of free, conjugated and bound PAs in leaves.     

脱落酸和己糖激酶抑制剂对高表达C4-PEPC转基因稻苗耐旱性的影响

为了研究高表达转玉米C₄-磷酸烯醇式丙酮酸羧化酶（phosphoenolpyruvate carboxylase,PEPC）基因水稻（PC）的耐旱性机制,本研究以PC和未转基因野生型原种kitaake为材料,分别在光照和黑暗预处理24 h,其中光照处理中光强为600 μmol·m^-2·s^-1,预处理后稻苗再在15％聚乙二醇-6000模拟干旱胁迫下,同时使用药理学的方法,通过加入脱落酸和己糖激酶的专一性抑制剂100 μmol·L^-1去甲二氢愈创木酸和10 mmol·L^-1葡萄糖胺,观察两种水稻4~5叶期稻苗耐旱表现。结果发现,与WT水稻相比,在PEG-6000处理后,经过光预处理的PC水稻叶片相对含水量下降较少,始终比WT的高,而且丙二醛含量则较少,脯氨酸诱导增加,表现耐旱;而经过暗预处理后PC植株显著降低这个优势,表明光预处理有利于PC耐旱性的表现;黑暗预处理均显著下调了2供试材料植株叶片中可溶性糖的含量,而对可溶性蛋白的含量影响不显著;而光预处理后PC水稻叶片内可溶性糖含量比WT增加,而在黑暗预处理则PC的显著低于WT的,其中葡萄糖胺对光预处理下PC的可溶性糖含量的下调作用最显著;暗预处理逆转或消除了NO,H₂O₂和钙离子含量变化趋势,这些变化与暗预处理减少了两材料叶片蔗糖和葡萄糖含量变化同步;光暗预处理对两材料的PEPC酶活性的差异影响不大,表明外源玉米C₄-PEPC在水稻中是组成型表达。可见PC叶片可部分通过糖组分,参与内源糖介导ABA和HXK信号途径,缓解干旱处理对叶片的伤害,稳定光合能力。     

干旱胁迫下牛心朴子幼苗相对含水量、质膜透性及保护酶活性变化

牛心朴子(Cynanchum komarovii)幼苗用不同浓度PEG-6000(聚乙二醇)模拟干旱处理,测定处理12d和复水24h中根、叶的RWC、质膜相对透性、MDA含量及几种保护酶(SOD、CAT、POD)活性变化情况,结果表明：高浓度胁迫后期,RWC明显下降,MDA含量增大,致使膜脂过氧化引起膜损伤;低、中浓度胁迫下,RWC下降程度低,细胞膜脂过氧化及膜透性影响小,且可能对膜脂过氧化起到一定的防御作用。复水后,低、中度胁迫下,各项指标能迅速恢复到CK水平,而高浓度胁迫下,除叶质膜透性、MDA含量、SOD活性不能恢复外,根、叶的其余指标均能达到CK水平。保护酶系统的作用,在一段时间内,可能是通过它们之间的相互协调而保持一个稳定的平衡态进行的。     

用渗透胁迫鉴定小麦种子萌发期抗旱性的方法分析

本以聚乙二醇(PEG)-6000、甘露醇和蔗糖作为渗透剂模拟水分胁迫,胁迫溶液渗透势范围在-0．25MPa到-1．50MPa,分析适于进行小麦种子水分胁迫萌发试验的条件,以鉴定小麦萌发期的抗旱性。结果表明,蔗糖溶液易诱发霉茵,胚芽不能正常生长。渗透势为-0．25MPa的PEG-6000及-0．50MPa的甘露醇胁迫已经显抑制了胚芽伸长;-0．50MPa的PEG-6000及-1．00MPa的甘露醇显抑制种子萌发,随着胁迫强度增加,种子相对发芽率及胚芽长度减小,主要是因为渗透胁迫降低了种子吸水速度,胚芽的相对含水量和渗透势均低。在渗透势相同的胁迫条件下,PEG-6000对小麦种子萌发各项检测值的抑制作用均大于甘露醇。如果目的是通过鉴定小麦种子在高渗溶液中的萌发情况,评价萌发期的抗旱性。选用-0．50MPa的PEG-6000或-1．00MPa的甘露醇较为理想,若同时考虑降低试验成本,则应首选-0．50MPa的PEG-6000。     

2种玉米幼苗耐旱性生理机制研究

以白种皮(白玉米)和黄种皮(黄玉米)2个玉米栽培品种为材料,在水培条件下进行聚乙二醇(PEG-6000)模拟干旱胁迫处理,分析玉米叶片抗旱性相关生理特性和质膜H+-ATP酶活性的变化,探讨2种玉米幼苗耐旱性生理机制。结果表明:(1)在2%、5%、10%PEG-6000处理条件下,随处理浓度和时间的增加,2种玉米幼苗植株失水率上升,叶片蒸腾速率降低,气孔传导率下降;在所有相同处理条件下,白玉米植株失水率明显小于黄玉米,而叶片蒸腾速率和气孔传导率下降幅度明显大于黄玉米,即白玉米的耐旱性比黄玉米强。(2)在相同浓度PEG-6000处理下,白玉米叶片可溶性蛋白、可溶性糖含量、游离脯氨酸含量均高于黄玉米,它在干旱胁迫下的渗透调节能力强于黄玉米。(3)在抗氧化酶体系中,随着PEG-6000胁迫浓度的升高,2种玉米叶片CAT活性呈下降趋势,但白玉米CAT活性在2%和5%PEG-6000胁迫下均显著高于黄玉米,其叶片中H2O2含量显著低于黄玉米。(4)随着PEG-6000胁迫浓度的升高,白玉米叶片质膜H+-ATPase磷酸化水平及其与14-3-3蛋白的结合受到的抑制作用比黄玉米强,白玉米叶片质膜H+-ATPase活性比黄玉米叶片低,叶片气孔开度小于黄玉米,叶片蒸腾速率和气孔传导率均低于黄玉米,这可能是白玉米耐旱性强于黄玉米的一个重要机制。     

Reflectance Indices Indicative of Changes in Water and Pigment Contents of Peanut and Wheat Leaves

Measurements of reflectance in visible and near-infrared spectral regions were made on detached leaves of two crop species of different leaf morphology, structure, and water content (peanut and wheat) throughout progressive desiccation. Relative water content (RWC) was well correlated with water index (WI) but even better with the ratio of WI and normalized difference vegetation index. RWC was also significantly correlated with structural independent pigment index indicative of carotenoids/chlorophyll ratio. New indication is thus provided to assess leaf water content and apply simple and fast radiometric techniques for plant water stress management. This revised version was published online in June 2006 with corrections to the Cover Date.     

The role of aquaporin RWC3 in drought avoidance in rice

Although the discovery of aquaporins in plants has resulted in a paradigm shift in the understanding of plant water relations, the relationship between aquaporins and drought resistance still remains elusive. From an agronomic viewpoint, upland rice is traditionally considered as showing drought avoidance. In the investigation of different morphological and physiological responses of upland rice (Oryza sativa L. spp indica cv. Zhonghan 3) and lowland rice (O. sativa L. spp japonica cv. Xiushui 63) to water deficit, we observed young leaf rolling and the remarkable decline of cumulative transpiration in the upland rice. The expression of water channel protein RWC3 mRNA was increased in upland rice at the early response (up to 4 h) to the 20% polyethylene glycol (PEG) 6000 treatment, whereas there was no significant expression changes in lowland rice. Protein levels were increased in upland rice and decreased in lowland rice at 10 h after the water deficit. The up-regulation of RWC3 in upland rice fits well with the knowledge that upland rice adopts the mechanism of drought avoidance. The physiological significance of this RWC3 up-regulation was then explored with the over-expression of RWC3 in transgenic lowland rice (O. sativa L. spp japonica cv. Zhonghua 11) controlled by a stress-inducible SWPA2 promoter. Compared to the wild-type plant, the transgenic lowland rice exhibited higher root osmotic hydraulic conductivity (Lp), leaf water potential and relative cumulative transpiration at the end of 10 h PEG treatment. These results indicated that RWC3 probably played a role in drought avoidance in rice.     

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.     

Effect of water deficit and sulphur dioxide on total soluble proteins,nitrate reductase activity and free proline content in sunflower leaves

Sunflower (Helianthus annus L. cv. PSH-7) plants were subjected to different osmotic potentials, using polyethylene glycol-6000 (PEG-6000), after, prior to and during SO₂ fumigation. Total soluble proteins and nitrate reductase activity (NRA) decreased, and free proline content increased with the increasing water stress. These biochemical parameters were more adversely affected in fumigated plants than in non-fumigated ones, when mild water stress was provided prior to and during fumigation. When severe water stress was given prior to and during fumigation, total soluble proteins, NRA and free proline content were nearly the same in fumigated and non-fumigated water-stressed plants; it is because the stomatal closure was observed in water-stressed plants. The leaf water potential decreased with the increasing water stress; however, it was not significantly affected due to SO₂ fumigation.     

干旱胁迫下紫花苜蓿幼苗非结构性碳水化合物代谢对NO的响应

以紫花苜蓿（Medicago sativa）为材料,采用盆栽试验方法,用聚乙二醇（PEG-6000）作为渗透介质模拟干旱胁迫,外源喷施NO供体硝普钠,NO清除剂（carboxy-PTIO,cPTIO）,对紫花苜蓿幼苗叶片、根系中非结构性碳水化合物含量及相关酶活性的变化进行研究,探讨NO对紫花苜蓿耐旱机制的作用。结果表明：外源NO促进了紫花苜蓿叶片中淀粉的分解、根系中淀粉的积累,提高叶片及根系中可溶性糖（蔗糖、果糖和葡萄糖）含量,降低了渗透势,促进细胞吸水,缓解干旱造成的损伤。此外,外源NO能提高干旱胁迫下紫花苜蓿叶片中蔗糖合成酶（SS）、酸性转化酶（AI）和中性转化酶（NI）活性,降低了蔗糖磷酸合成酶（SPS）的活性,提高根系中SS、SPS和转化酶活性,使蔗糖的合成与分解处于高水平的动态平衡,增强了紫花苜蓿的抗旱性。而NO清除剂cPTIO则会不同程度的抑制紫花苜蓿幼苗中非结构性碳水化合物（NSC）及其相关酶活性。因此,NO可以通过调控NSC的代谢响应干旱胁迫,缓解干旱胁迫造成的不利影响,在紫花苜蓿的抗旱中扮演着重要的角色。     

PEG模拟干旱条件下木麻黄幼苗的生理变化

以木麻黄Casuarina equisetifolia15个家系品种为材料,利用聚乙二醇6000(PEG-6000)模拟水分胁迫环境,设置三个胁迫强度处理(轻度、中度、重度胁迫),研究受胁迫2月龄木麻黄幼苗丙二醛(MDA)含量、超氧化物歧化酶(SOD)活性、脯氨酸含量的变化。结果表明,经干旱胁迫处理后,各家系幼苗叶片MDA含量随胁迫强度增大而增大,但增幅差异较大;不同干旱胁迫水平下,各家系SOD活性存在一定差异;重度胁迫条件下,除粤杂交家系外,其余家系脯氨酸含量与对照相比均为显著增加。采用主成分分析法进行抗旱性综合评价,表明MDA含量是反映水分胁迫最重要的指标。各指标综合分析结果表明,家系701、莆20、抗3、惠2、南山7和东山2抗旱性能力较好;东山短、601、59、A13抗旱能力一般;千头、粤杂交、抗1、龙4和平5抗旱能力较差。     

A simple procedure to overcome polyethelene glycol toxicity on whole plants

A procedure is described that can be used to minimize toxic effects of polyethylene glycol (PEG) to plants. The procedure is based on recycling nutrient solutions containing PEG-6000 through two plant cultures. Tomato plants grown in −0.3 megapascals PEG solutions used after two growth cycles exhibited minimal toxic effects. Long-term responses like dry matter production and chlorophyll content as well as short-term responses like CO₂ fixation rates and leaf conductance were severely inhibited by fresh PEG-6000 and only slightly reduced by recycled PEG-6000. Complete osmotic adjustment was obtained with tomatoes grown in recycled but not in fresh PEG solutions.     

Coronatine Alleviates Water Deficiency Stress on Winter Wheat Seedlings

With the aim to determine whether coronatine(COR) alleviates drought stress on wheat,two winter wheat(Triticum aestivum L.) cultivars,ChangWu134(drought-tolerant) and Shan253(drought-sensitive) were studied under hydroponic conditions.Seedlings at the three-leaf stage were cultured in a Hoagland solution containing COR at 0.1 μM for 24 h,and then exposed to 20% polyethylene glycol 6000(PEG6000).Under simulated drought(SD),COR increased the dry weight of shoots and roots of the two cultivars significantly;the root/shoot ratio also increased by 30% for Shan253 and 40% for ChangWu134.Both cultivars treated with COR under SD(0.1COR+PEG) maintained significantly higher relative water content,photosynthesis,transpiration,intercellular concentration of CO2 and stomatal conductance in leaves than those not treated with PEG.Under drought,COR significantly decreased the relative conductivity and malondialdehyde production,and the loss of 1,1-diphenyl-2-picrylhydrazyl scavenging activity in leaves was significantly alleviated in COR-treated plants.The activity of peroxidase,catalase,glutathione reductase and ascorbate peroxidase were adversely affected by drought.Leaves of plants treated with COR under drought produced less abscisic acid(ABA) than those not treated.Thus,COR might alleviate drought effects on wheat by reducing active oxygen species production,activating antioxidant enzymes and changing the ABA level.     

外源Ca2+对PEG处理下转C4型PEPC基因水稻光合生理的调节

磷酸烯醇式丙酮酸羧化酶(PEPC)通过固定二氧化碳参与光合作用, 是关键的C₄植物光合作用酶。为了揭示高光效转C₄ PEPC基因水稻(Oryza sativa)对干旱胁迫的适应机理, 以高表达转C₄ PEPC水稻(PC)和野生型水稻Kitaake (WT)为供试材料, 在植株的4-5叶期, 使用不同浓度外源CaCl₂溶液处理, 测定在15%聚乙二醇6000 (polyethylene glycol-6000, PEG-6000)胁迫下叶片相对含水量、光合参数、内源钙总含量、叶片总蛋白激酶活性、PEPC酶活性以及相关基因表达和蛋白质含量。结果表明, 0.5 mmol∙L^-1 CaCl₂明显提高PC叶片相对含水量(P<0.05), 2 mmol∙L^-1和10 mmol∙L^-1 CaCl₂则作用不显著, 对WT则影响不显著。不同浓度钙处理对PEG处理PC的净光合速率影响不显著, 而通过维持气孔导度减少水分胁迫。内源总钙浓度的数据显示, 在PEG6000处理下, PC具有维持稳定内源Ca²⁺浓度的能力, 过高浓度(10 mmol∙L^-1 CaCl₂)钙处理反而降低了PEPC酶活性、PEPC基因表达和可溶性蛋白的含量。     

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.