水分胁迫和胁迫后复水对玉米叶片生长速率的影响

玉米叶片延伸速率(LER)对水分状况的变化很敏感。快速干旱处理,水分消耗迅速,LER从最大到零需5h,叶水势改变0.5～0.6 MPa,缓慢干旱处理,水分消耗较慢,LER从最大到零需20h,叶水势改变1 MPa。缓慢干旱植株叶片成熟部位的渗透势,在任何LER下,均比快速干旱叶片更负。LER为零时,快速干旱叶渗透势为-1.3 MPa,缓慢干旱为一1.6MPa左右。短时间水分胁迫后复水,LER迅速增加,有部分补偿前期胁迫减少的生长量能力;长时间水分胁迫后复水,LER在6 h内不可能恢复到正常水平。     

水分胁迫下高粱叶片的渗透调节与延伸生长的关系

高粱抗旱品种3197B比不抗旱品种三尺三在水分胁迫条件下ψ_S下降低。在相同ψ_S时,3197B相对含水量高于三尺三。水分胁迫期间,3197B能始终维持比三尺三较高的ψ_P。在中度和严重水分胁迫时,3197B几种渗透物质积累均高于三尺三,其中可溶性糖和K~ 对渗透调节贡献最大。水分胁迫下,3197B正展开叶渗透调节能力较强,ψ_P维持较高,临界膨压低,叶片扩张性能小、故生长速率随ψ_W下降较慢。     

温度和水分状况对几种不同类型植物叶片水势和延伸生长的影响

在田间条件下研究了温度、相对湿度、土壤水分对玉米、高粱、茄子、豇豆、河北杨和泡桐六种植物LER2)和ψWL3)日变化的影响。结果表明,ψWL日变化呈正弦曲线,即早晨、晚上高,中午低;土壤水分亏缺,中午大气ψWV4)愈低,ψWL降低愈多。在土壤供水良好的条件下,玉米、高粱、河北杨、泡桐叶片生长与温度密切相关,因此白天生长快,晚上生长慢;若中午ψWV太低,生长减慢,使叶片生长呈双峰曲线,即午前及18:00左右生长快。若土壤水分亏缺,白天ψWV太低,白天生长慢,晚上生长快。茄子和豇豆叶片生长对水分亏缺更敏感,晚上生长快,白天生长慢,干旱处理叶片在白天中午有收缩现象。     

小麦叶片光合作用与其渗透调节能力的关系

在缓慢干旱条件下,小麦叶片渗透调节能力在一定范围内随胁迫程度的加剧而增加,而在快速干旱下,渗透调节能力丧失。小麦叶片通过渗透调节使光合速率和气孔导度对水分胁迫的敏感性降低,叶片维持较高的电子传递能力、RuBP羧化酶活性和叶绿体光合能量转换系统活性,并推迟了小麦叶片光合速率受气孔因素限制向叶肉细胞光合活性限制转变的时间。     

4种沙生灌木幼苗PV曲线水分参数对干旱胁迫的响应

以柠条、沙木蓼、杨柴和花棒4种沙生灌木幼苗为材料,采用盆栽法在适宜水分、中度干旱和重度干旱(田间持水量的75%、50%和35%)3种土壤水分条件下,应用PV技术测定了它们在膨压为0时的渗透势(ψstlp)、相对水含量(RWCtlp)和相对渗透水含量(ROWCtlp),以及饱和含水时的渗透势(ψssat)、束缚水含量(Va)、膨压随叶水势下降而降低的速率b值和组织细胞总体弹性模量(ε′)等水分参数,并用隶属函数值法对4种苗木在干旱下保持膨压的能力进行了综合评价.结果显示:与适宜水分条件下相比较,除花棒幼苗在中度及重度干旱下ψssat值、柠条苗在中度干旱下ψssat和ψstlp差值和在中度及重度干旱下Va值、沙木蓼苗在中度干旱下ε′和RWCtlp值均变化很小以外,4种苗木其它水分参数在不同程度干旱胁迫下均有较明显的变化,且其变化幅度随干旱胁迫的加剧而增加,从而使苗木保持膨压及吸水保水的能力较适宜水分下明显增强;苗木保持膨压能力的综合评价结果为:中度干旱下柠条>花棒>杨柴>沙木蓼,重度干旱下柠条>花棒>沙木蓼>杨柴.研究表明,柠条幼苗对干旱胁迫具有极强的渗透调节适应性.     

水分胁迫下不同抗旱类型品种对氮素营养反应的比较研究

实验结果表明,小麦受到水分胁迫时,游离脯氨酸大量积累,胁迫缓慢加重时,渗透调节能力增强,适当的氮素营养,可增强渗透调节作用,有助于干旱下维持膨压,提高NR酶活性和净光合速率。水地型品种对水分和氮素营养都较敏感,叶片水势、饱和渗透势、NR酶活性、游离脯氨酸含量的变化都较旱地型品种大,旱地型品种在受旱时水分状况较稳定,生理代谢变化幅度较小,但两类旱地品种对氮素营养的反应不同。旱肥型较旱薄型敏感。水分胁迫下,水地型品种渗透势下降较多,渗透调节幅度较大,是对逆境更敏感或实际受到的胁迫较重的表现。     

盐分和水分胁迫对芦荟幼苗渗透调节和渗调物质积累的影响

用不同浓度NaCl和等渗聚乙二醇(PEG 6000)处理芦荟(Aloe vera L.)幼苗,10 d后测定叶片相对生长速率和厚度、叶片中主要有机溶质、无机离子含量及渗透调节能力.结果表明,-0.44、-0.88 MPa NaCl和PEG处理使芦荟叶片的相对生长速率和叶片厚度明显下降,且盐胁迫对幼苗生长的抑制和叶片含水量降低的效应明显高于等渗的水分胁迫,其叶片渗透调节能力随处理渗透势的降低而增加, -0.88 MPa PEG胁迫的芦荟幼苗的渗透调节能力高于等渗盐分胁迫.在主要渗透调节物质可溶性糖、有机酸、K 、Ca2 和Cl-中,-0.88 MPa PEG处理下含量比相同渗透势的NaCl处理下显著增加的是有机溶质,因此推断有机溶质含量高是PEG胁迫下渗透调节能力较强的主要因素.     

植物渗透调节的测定方法介绍

渗透调节是植物适应水分胁迫的主要生理机制。其含义是植物在逆境(干旱或盐渍)条件下,通过代谢活动增加细胞内溶质浓度,降低其渗透势(从而降低水势),从外界水势降低的介质中继续吸水,保持一定的膨压,维持较正常的代谢活动。在干旱条件下受膨压影响的细胞生长、气孔开放、光合作用及酶活性等生理过程得到完全或部分的维持,有利于增强植物的抗旱能力。国外这     

美国海滨桤木和薄叶桤木水分生理特性的比较

采取盆栽、人工控水的方式, 研究并比较了美国本土海滨桤木(Alnus maritima)和薄叶桤木(A. incana)的气孔导度(G_s)、叶片水势(ψ_leaf)以及渗透调节能力对土壤水分条件的响应, 以探讨引起两种桤木生态分布差异巨大的生理生态原因。结果表明: 1)正常水分条件下, 海滨桤木的G_s低于薄叶桤木, 其与大气温度、相对湿度和水蒸气亏缺等气象因子的相关性低于薄叶桤木; 干旱胁迫下, 海滨桤木的G_s对其自身ψ_leaf下降信号的敏感度低于薄叶桤木; 复水后, 其G_s恢复更为缓慢。2)正常水分条件下, 海滨桤木的ψ_leaf高于薄叶桤木, 且引起气孔关闭的ψ_leaf临界值较高; 干旱胁迫下, 海滨桤木的ψ_leaf下降幅度高于薄叶桤木。3)正常水分条件下, 海滨桤木和薄叶桤木的渗透调节能力无显著差异; 干旱胁迫下, 尽管两种桤木均表现出饱和状态渗透势(ψ_s^sat)下降、膨压与水势关系的最大变化率降低、初始失膨点渗透势(ψ_s^tlp)增加、细胞渗透调节能力范围(ψ_s^sat-ψ_s^tlp, Dψ_s)减小的趋势, 但与薄叶桤木相比, 海滨桤木的ψ_s^tlp较高, Dψ_s较小。从以上生理生态指标可以看出, 较高的叶片水势、较低的气孔调节能力、干旱下较低的渗透调节能力是造成海滨桤木分布范围狭小的重要原因。     

土壤干旱对元宝枫渗透调节能力的影响

采用盆栽控水法和P—V技术研究分析了不同土壤干旱(速度、程度)条件对元宝枫渗透调节能力的影响。结果表明,元宝枫具有很强的渗透调节能力．但该能力受土壤干旱的速度和程度影响,在缓慢干旱条件下,元宝枫叶片的ψw、ψ0、π100、RWC^0、ROWC^0均明显降低．其中与渗透调节能力直接相关的(π100可下调0．52MPa,ψ0下调1．51MPa。在快速干旱条件下π100和ψ0分别仅下凋0．20MPa和0．48MPa。△π100值也表明缓慢干旱条件下元宝枫渗透调节能力是快速干旱下的45倍。在缓慢干旱条件下．由轻度到中度干旱时其渗透调节能力显著增强(增加270％);由中度到严重干旱时．增加不明显(增加了24．5％)。从3种有机渗透调节物质含量与△π100值的动态变化可见,可溶性糖含量增加对渗透调节能力的贡献是第一位的．其次是Pro、游离氨基酸。     

Leaf age and salinity influence water relations of pepper leaves

Plant growth is reduced under saline conditions even when turgor in mature leaves is maintained by osmotic adjustment. The objective of this study was to determine if young leaves from salt-affected plants were also osmotically adjusted. Pepper plants (Capsicum annuum L. cv. California Wonder) were grown in several levels of solution osmotic potential and various components of the plants' water relations were measured to determine if young, rapidly growing leaves could accumulate solutes rapidly enough to maintain turgor for normal cell enlargement. Psychrometric measurements indicated that osmotic adjustment is similar for both young and mature leaves although osmotic potential is slightly lower for young leaves. Total water potential is also lower for young leaves, particularly at dawn for the saline treatments. The result is reduced turgor under saline conditions at dawn for young but not mature leaves. This reduced turgor at dawn, and presumably low night value, is possibly a cause of reduced growth under saline conditions. No differences in leaf turgor occur at midday. Porometer measurements indicated that young leaves at a given salinity level have a higher stomatal conductance than mature leaves, regardless of the time of day. The result of stomatal closure is a linear reduction of transpiration.     

TRPV4在渗透压对大鼠心肌收缩性影响中的作用

本文旨在探讨低渗和高渗内环境对心肌收缩性的影响及机制.取Sprague-Dawley(SD)大鼠左心室乳头状肌,在电刺激引起兴奋的条件下,分别记录在低渗、等渗和高渗灌流液中肌条的收缩力;同样条件下观察在低渗、等渗和高渗灌流液中加入渗透压敏感蛋白瞬时感受器电位离子通道家族香草素受体亚家族IV型(transient receptor potential vanilloid 4,TRPV4)的拮抗剂和激动剂后肌条收缩力的变化.结果显示:(1)与等渗(310 mOsm/L)时心肌收缩力相比,渗透压为290、270和230 mOsm/L时心肌收缩力分别增加11.5%、21.5%、25.O%(P<0.05);渗透压为350、370、390 mOsm/L时心肌收缩力分别降低16.0%、23.7%、55.2%(P<0.05).(2)在低渗液(270 mOsm/L)中加入TRPV4拮抗剂钌红(ruthenium red,RR),低渗对心肌收缩力的增强作用被抑制36%(P<0.01);在高渗液(390 mOsm/L)中加入RR,高渗对心肌收缩力的抑制作用增加56.1%(P<0.01).(3)在等渗液中(310 mOsm/L)加入TRPV4激动剂4-α-佛波醇-12,13-二癸酸(4-α-phorbol-12,13-didecanoate,4 α-PDD),心肌收缩力没有改变;在高渗液中(390 mOsm/L)加入4α-PDD,高渗对心肌收缩力的抑制作用增加27.1%(P<0.01).以上结果提示,TRPV4参与渗透压引起的心肌收缩力变化.     

Osmotic adjustment in indoor grown cassava in response to water stress

The water content-water potential relation in stressed and unstressed cassava ( Man-ihot species) was examined to ascertain (i) the magnitude of osmotic adjustment in response to water stress and (ii) the mechanisms of such adjustments.
Water stress resulted in a displacement of the water content-potential relation such that at any leaf water potential the water content was higher in the stressed plants. The osmotic potentials of turgid leaves (100% relative water content) were -0.97 and -1.00 MPa in the unstressed cultivars CMC 9 and MCOL 113 respectively. In the stressed plants, the values were-1.13 MPa (CMC 9) and-1.14 MPa (MCOL 113). The 0.14 to 0.16 MPa osmotic potential difference between the stressed and unstressed plants suggests that a stress-induced osmotic adjustment occurred in both cultivars. The biiSk volumetric elastic moduli at turgor pressures above 0.10 MPa were 9.84 MPa (CMC 9) and 13.58 MPa (MCOL 113) in the unstressed plants. Tbe higher values found in the stressed plants, 14.56 MPa in CMC 9 and 16.91 MPa in MCOL 113, suggest a stress-induced decrease in cell wall elasticity. Hence, the observed shift in the wafer content-potential relations in the cassava involved both an osmotic adjustment and a decrease in cell wall elasticity. Increasing the number of stress cycles per plant did not cause a further displacement of the water content-potential curves.     

Water relations of Capsicum genotypes under water stress

Pepper species and cultivars, Capsicum annuum cv. Bell Boy, C. annuum cv. Kulai and C. frutescens cv. Padi, differing in drought tolerance were investigated for their water relations, stomatal responses and abscisic acid (ABA) content during water stress. C. frutescens cv. Padi exhibited a greater osmotic adjustment than C. annuum cultivars. Stomatal conductance of cv. Bell Boy was more sensitive to water stress than that of cvs. Kulai and Padi. In all pepper genotypes, stomatal closure was triggered in the absence of a large decrease in leaf water status. ABA content in xylem sap and leaf was higher in C. annum cultivars compared to C. frutescens cv. Padi. This revised version was published online in July 2006 with corrections to the Cover Date.     

Discrepancies between water potential isotherm measurements on Pinus ponderosa seedling shoots: xylem hysteresis and apoplasmic osmotic potentials *

Abstract. Sap expression, air drying and a combined technique were used to measure the water potential isotherm of Pinus ponderosa Laws, seedling shoots with the pressure chamber. Discrepancies between water relations parameters derived from these techniques can be partially explained by air entry into air drying tissues, hysteresis in the xylem water potential isotherm and dilution of apoplasmic solutes during sap expression.     

Changes at panicle emergence in the water relations of a wetland and a dryland Japonica rice cultivar under wetland conditions

The diurnal and seasonal changes in plant water relations of two Japonica rice ( Oryza sativa L.) cultivars, Nipponbare and Tachiminori, were studied under flooded conditions at Kyoto University. The dryland cv. Tachiminori maintained higher predawn and midday leaf osmotic potentials relative to the wetland cv. Nipponbare during the vegetative stage, but the ranking was reversed after flowering. The relationship between leaf water potential and leaf osmotic potential showed that prior to panicle emergence Nipponbare was able to adjust osmotically to maintain turgor, whereas after heading there was little turgor maintenance. Tachiminori showed little difference in osmotic adjustment before and after panicle emergence. Fertilizer treatment during panicle development also helped to maintain the degree of osmotic adjustment in both cultivars.     

An Impasse in Plant Water Relations?

Balling and Zimmermann [Planta 182 (1990), 325–338] used a pressure probe to measure directly negative pressures in the xylem of transpiring plants. They obtained data that challenge the standard framework that plant physiologists use when thinking about plant water relations, and, most notably, found a substantial discrepancy between their measurements of xylem pressure and of leaf water potential measured with a Scholander pressure bomb. Their data are critically examined and it is shown that most of them can be accommodated within the established principles of plant water relations. In particular, there are several reasons, consistent with the established principles, why leaf water potential and xylem pressure may differ.     

A new equation for calculating osmotic potential

A new equation for calculating osmotic potential was developed that is based on a molecular model of the structure of water. Its formulation involves no sub-equations that cannot be fully derived from established physical principles. The equation was first tested by calculating the osmotic potentials of a series of aqueous NaCl solutions with concentrations ranging from 0.103 to 4.382 kmol m⁻³, and comparing those calculations with calculations made using equations recorded in the literature. Virtually the same results were obtained. Subsequently, it was tested successfully by comparative calculations on a selection of inorganic and organic aqueous solutions. The principles it embodies provide for the visualization of the molecular role of water in plants as a unifying mechanism. Factors that affect the size of the structure of water, and the consequent distance an individual molecule must travel to and fro across its cage, determine direction and rate of flow. It is considered that the equation will provide a new research tool for many osmotic-potential-related questions.     

The mechanism of boron tolerance for maintenance of root growth in barley (Hordeum vulgare L.)

Cultivar differences in root elongation under B toxic conditions were observed in barley (Hordeum vulgare L.). A significant increase in the length and width of the root meristematic zone (RMZ) was observed in Sahara 3771 (B tolerant) when it was grown under excessive B concentration, compared to when grown at adequate B supply. This coincided with an increase in cell width and cell numbers in the meristematic zone (MZ), whereas a significant decrease in the length and no significant effect on the width of the MZ was observed in Clipper (B intolerant) when it was grown under excessive B supply. This was accompanied by a decrease in cell numbers, but an increase in the length and width of individual cells present along the MZ. Excessive B concentrations led to a significantly lower osmotic potential within the cell sap of the root tip in SloopVic (B tolerant) and Sahara 3771, while the opposite was observed in Clipper. Enhanced sugar levels in the root tips of SloopVic were observed between 48 and 96 h after excess B was applied. This coincided with an increase in the root elongation rate and with a 2.7-fold increase in sucrose level within mature leaf tissue. A significant decrease in reducing sugar levels was observed in the root tips of Clipper under excessive B concentrations. This coincided with significantly lower root elongation rates and lower sucrose levels in leaf tissues. Results indicate a B tolerance mechanism associated with a complex control of sucrose levels between leaf and root tip that assist in maintaining root growth under B toxicity.