干旱胁迫下植物根源化学信号研究进展

土壤干旱胁迫诱导植物根系产生根源化学信号,经运输系统长距离传输到地上部分,降低气孔导度,抑制蒸腾作用,从而提高植物的水分利用效率。根源化学信号包括脱落酸(ABA)、细胞分裂素(CTK)、生长素、木质部pH值和钙离子(Ca²⁺)等,其中以ABA为主的植物根源信号通路研究得最为广泛和深入。总结了几种主要的化学根源信号物质的基本性质、主要功能和调节机制,重点对这些信号参与气孔行为、差别基因表达和生长发育方面的研究进展进行了综述。由于干旱条件下植物根源信号反应涉及到从分子到群体的一系列复杂过程,各种信号的生理效应呈现交互作用、耦合发生的特点,今后的热点领域将集中在研究交互网络中合成的的关键物质和揭示这些物质在分子及生理水平上的作用机理上。根源化学信号研究正朝向"以分子和生理研究为基础、不同尺度的结构和功能耦合"的方向发展。     

根系分区灌溉和水分利用效率

根系分区灌溉是指仅仅部分根系受到正常的灌溉,其余根系则受到人为的干旱,两项理论根据指出这种措施可减少植物的水分肖耗,并保持一定的生物产量,其一是植物蒸腾失水与气孔导性是线性关系,而光合作用与气孔导性则是一种渐趋饱和的关系,如果气孔导性从最大值适应调低,可显著降低蒸腾,但对光合影响应小得多,其二是处于干燥土壤中的根系可感觉干旱,产生干旱信号来调节地上部分的气孔开度,显然,这项措施在田间有多大效用值得深入研究。 先是大田作物的蒸腾失水仅部分地受气孔控制,界面层的扩散阻力起很大作用。因此该措施可能对界面层阻力较小的,如果树等作用大些,另外,根系干旱信号可否“长期”地产生和调控气孔仍需试验证明。     

交替灌溉的节水调质机理及同位素技术在作物水分利用研究中的应用

基于节水灌溉技术原理与作物感知缺水的根源信号理论而提出的根系分区交替灌溉,是交替对作物部分根区进行正常的灌溉,其余根区受到适度水分胁迫的灌溉方式。应用同位素示踪技术追溯分根区交替供水条件下土壤-作物系统水分运转途径并揭示其节水调质机理是一个重要的研究方向。本文对根系分区交替灌溉的节水调质效应、节水机理、稳定性氢氧同位素在植物水分运移中的应用以及稳定性碳同位素在植物水分利用效率中的应用研究进展及应用前景作了简要介绍,并对将来需要重点研究的方向作了展望。以期为充分挖掘作物生理节水潜力,大幅度提高作物水分利用效率和实现节水、丰产、优质、高效的综合目标提供有效的调控途径。     

交替灌溉对山黧豆叶片气体交换和土壤水分以及产量指标的影响

改变土壤根系的分布以汲取深层土壤水分的能力是植物避免干旱的主要策略。山黧豆是一种抗逆性强的豆类作物,该研究通过起垄条播控制性沟灌的方式,设置传统灌溉(FI)、交替灌溉(PRD,灌水量减少50%)和不灌溉(NI)3种处理模式,探索不同灌溉模式对播种后不同时期山黧豆土壤水分、根系分布、叶片气体交换、水分利用效率和籽粒产量的影响。结果表明：(1)在FI、PRD和NI处理下,山黧豆的根系分别有89.8%、86.9%和84.9%生长在0~20 cm的表层土壤中;干旱胁迫使PRD和NI处理下深层土壤中根系的比例提高至13.05%和15.07%。(2)在整个生育期内,土壤干旱显著降低了山黧豆叶片的净光合速率、蒸腾速率和气孔导度;在种植后60 d时,PRD和NI处理下叶片的瞬时水分利用效率分别较FI处理显著提高了21.4%和14.9%。(3)干旱胁迫显著降低了山黧豆植株高度、第一豆荚高、平均结荚数和豆粒数以及地上部和根系的干重,但显著增加了根冠比;PRD处理对豆荚长度、豆荚重和每荚豆粒重没有显著影响;PRD和NI处理下山黧豆平均籽粒产量分别比FI处理显著降低了53%和63%。研究发现,在干旱胁迫条件下,山黧豆能够通过提高深层土壤中根系的比例、更多吸收深层土壤水分、显著增加根冠比以及显著提高生殖生长期叶片的瞬时水分利用效率,减轻干旱胁迫对自身生长的影响。该研究结果可为山黧豆在旱区推广种植提供理论依据。     

模拟喀斯特不同土壤生境下黑麦草对水分胁迫的生长和光合生理响应

以多年生草本黑麦草为对象,模拟喀斯特生境土壤特征设置浅而宽(Shallow and wide, SW:30×30×5 cm~3)和深而窄(Deep and narrow, DN:10×10×45 cm~3)两种土壤容器,以正常降水量为对照供水(W100%),设减水50%(W50%)和减水70%(W30%)共3种水分处理进行盆栽实验,探究了两种不同土壤生境中土壤水分变化对黑麦草生长及光合生理的影响,以进一步理解喀斯特地区植物的适应对策。结果显示:(1)SW生境对水分变化敏感,随供水减少土壤含水量显著下降。轻度减水下植物叶面积增大,光合速率提高,地上部分生长得到促进,但水分严重减少对其生长和光合生理有抑制作用,但地上质量分数和水分利用效率却显著升高;(2)DN生境保水能力较好,随供水减少土壤水分含量下降较为平缓。叶片相对含水量、气孔导度和比叶面积在各水分处理之间差异不显著,但严重减水条件下总生物量、地上质量分数和水分利用效率均有回升。研究表明:浅而宽生境中植物倾向于通过提高地上部分的生长,保持较高的光合速率,并向地上部分分配较多生物量来应对水分胁迫;而深而窄生境中植物会充分利用土壤空间条件,促进根系的生长来提高对水分的吸收,从而维持植物的生长。     

土壤水分亏缺条件下根源信号ABA参与作物气孔调控的数值模拟

建立了根系吸水模型和根源ABA参与作物气孔调控过程相耦合的气孔导度模型,该模型在根源信号ABA的产生项中考虑了根系吸水影响函数和根系密度分布函数.利用该耦合模型模拟大田状况下根源ABA参与玉米气孔行为调控过程,结果表明,由于充分考虑了根区土壤水势和土壤中根长密度分布对根系吸水的影响,较好地反映了土壤不同层次根系吸水强度,更为确切地描述了当土壤水分亏缺时,根系合成ABA的量、各层根系蒸腾流中ABA浓度、木质部ABA浓度以及最终ABA参与对气孔行为的调控作用.     

夏玉米苗期有限水分胁迫拔节期复水的补偿效应

以作物调亏灌溉原理为基础 ,对夏玉米苗期水分胁迫拔节期复水进行了试验研究。结果表明 ,复水增加了夏玉米叶片气孔导度和光合速率 ,提高叶片水平上的水分利用效率(WUE)。复水 2天后 ,叶片气孔导度和光合速率即恢复到对照水平 ,部分时段 ,特别在下午 ,复水处理表现出高于对照的“反冲”现象。复水使苗期受旱的夏玉米株高、叶面积、地上 (下 )部分干物重和根系生长发育都恢复到或接近充分供水的植株生长水平。使其产量及构成因子与对照接近 ,水分利用效率显著地提高了 2 4 7%。这为玉米中后期的水分管理 ,提高玉米水分利用效率 ,提供了一定的理论依据 ;也提供了一种便于广大农民掌握的简单易行的灌溉方式     

红砂幼苗根系形态特征和水分利用效率对土壤水分变化的响应

为探讨干旱与半干旱区受损红砂种群幼苗适宜生长的土壤水分条件,采用盆栽方法,研究了红砂幼苗在充分灌溉(FI)、适度灌溉(MI)、干旱处理(DT)3个水分处理下根系形态和水分利用效率的变化特征。结果表明:(1)红砂幼苗根系形态因水分条件和根序的不同而各异;随灌溉量的减少红砂幼苗根系直径和根体积均表现为FIMIDT,但干旱处理促进了根系的伸长生长和比表面积和比根长增加,根系形态的可塑性是红砂幼苗获取水分适应干旱环境的重要策略之一。(2)随根序的升高,各处理水平下红砂幼苗根长、比根长均显著减少,而其根直径和体积却显著增加,表明红砂幼苗根系内部具有高度的形态异质性。(3)与FI处理相比,MI和DT处理下红砂幼苗根系总生物量分别增加了50.00%、19.23%,但MI和DT处理却显著降低了红砂幼苗地上生物量,特别是叶片生物量下降幅度最大,分别降低了62.15%、83.28%,导致根冠比随灌溉量的减少而逐渐增加。(4)干旱处理显著提高了红砂幼苗的水分利用效率。研究认为,在灌溉量减少的情况下,红砂幼苗可通过根长、根系表面积和体积、直径等形态变化来优化其空间分布构型,以调节植株对水分的利用,提高水分利用效率。     

干旱下植物气孔运动的调控

概述了植物气孔对大气干旱和土壤干旱的反应,认为植物气孔对大气干旱的反应并不是一种反馈机制;并就干旱条件下植物气孔运动的水力学和化学信号调控机制进行了简要论述,认为虽然化学信号调控干旱下气孔运动更为广泛,但ABA不是唯一的化学信号,水分关系影响了信号的产生、运转和气孔对信号的敏感性,干旱条件下水力学和化学信号共同调控着植物的气孔运动。     

杨柴对高CO2浓度和土壤干旱胁迫的响应

毛乌素优势植物杨柴 (HedysarummongolicumTurcz.)对高CO2 浓度和土壤干旱胁迫响应的研究结果表明 :干旱胁迫可使杨柴根系伸长 ,根生物量、地径、主茎高和茎生物量下降 ;高CO2 浓度使杨柴根和茎生物量明显增加 ,CO2 的“施肥效应”显著 ,干旱使CO2 的“施肥效应”减弱。同时 ,土壤干旱胁迫使杨柴的根 /冠比增加 ,说明在土壤干旱胁迫情况下根的生长比地上部分 (茎 )的生长更活跃 ,有利于提高杨柴在干旱沙漠地区的固沙作用 ;CO2 浓度升高和土壤干旱胁迫均使杨柴叶片的水势下降 ,叶片水势的下降使叶片细胞对水分的束缚力增强 ,从而减少植物蒸腾耗水 ,有利于提高水资源的利用效率     

Long-distance ABA Signaling and Its Relation to Other Signaling Pathways in the Detection of Soil Drying and the Mediation of the Plant’s Response to Drought

In this article we review evidence for a variety of long-distance signaling pathways involving hormones and nutrient ions moving in the xylem sap. We argue that ABA has a central role to play, at least in root-to-shoot drought stress signaling and the regulation of functioning, growth, and development of plants in drying soil. We also stress the importance of changes in the pH of the leaf cell apoplast as influenced both by edaphic and climatic variation, as a regulator of shoot growth and functioning, and we show how changes in xylem and apoplastic pH can affect the way in which ABA regulates stomatal behavior and growth. The sensitivity to drought of the pH/ABA sensing and signaling mechanism is emphasized. This allows regulation of plant growth, development and functioning, and particularly shoot water status, as distinct from stress lesions in growth and other processes as a reaction to perturbations such as soil drying.     

Modulation of Root Signals in Relation to Stomatal Sensitivity to Root-sourced Abscisic Acid in Drought-affected Plants

Stomatal sensitivity to root signals induced by soil drying may vary between environments and plant species. This is likely to be a result of the interactions and modulations ámong root signals. As a stress signal, abscisic acid （ABA） plays a central role in root to shoot signaling, pH and hydraulic signals may interact with ABA signals and thus, jointly regulate stomatal responses to changed soil water status, pH itself can be modified by several factors, among which the chemical compositions in the xylem stream and the live cells surrounding the vessels play crucial roles. In addition to the xylem pH, more attention should be paid to the direct modulation of leaf apoplastic pH, because many chemical compositions might strongly modify the leaf apoplastic pH while having no significant effect on the xylem pH. The direct modulation of the ABA signal intensity may be more important for the regulation of stomatal responses to soil drying than the ABA signal per se. The ABA signal is also regulated by the ABA catabolism and the supply of precursors to the roots if a sustained root to shoot communication of soil drying operates at the whole plant level. More importantly, ABA catabolism could play crucial roles in the determination of the fate of the ABA signal and thereby control the stomatal behavior of the root-sourced ABA signal.     

Modulation of Root Signals in Relation to Stomatal Sensitivity to Root-sourced Abscisic Acid in Drought-affected Plants

Stomatal sensitivity to root signals induced by soil drying may vary between environments and plant species. This is likely central role in root to shoot signaling. pH and hydraulic signals may interact with ABA signals and thus, jointly regulate stomatal responses to changed soil water status. pH itself can be modified by several factors, among which the chemical compositions In the xylem stream and the live cells surrounding the vessels play crucial roles. In addition to the xylem pH,more attention should be paid to the direct modulation of leaf apoplastic pH, because many chemical compositions might strongly modify the leaf apoplastlc pH while having no significant effect on the xylem pH. The direct modulation of the ABA signal intensity may be more important for the regulation of stomatal responses to soil drying than the ABA signal per se.The ABA signal is also regulated by the ABA catabolism and the supply of precursors to the roots If a sustained root to shoot communication of soil drying operates at the whole plant level. More importantly, ABA catabolism could play crucial roles In the determination of the fate of the ABA signal and thereby control the stomatal behavior of the root-sourced ABA signal.     

土壤干旱条件下氮素营养对玉米内源激素含量影响

在田间持水量分别保持于35％、55％和75％±5％的土壤水分条件下,利用盆栽实验研究了土壤干旱和氮素营养对玉米内源激素和气孔导度的影响．结果表明,土壤干旱下氮素营养明显降低了玉米根系木质部汁液ABA浓度,而正常供水下施氮处理间则无显著差异(施氮处理仍较低),同时测定的叶片ABA浓度则呈相反的变化趋势,表现为干旱下施氮处理要高于不施氮处理;施氮处理木质部汁液中ZRs浓度应低于相应的不施氮处理,在调控气孔行为方面并未表现拮抗ABA作用;3种土壤水分条件下,施氮玉米叶片的气孔导度均高于不施氮处理,与木质部汁液ABA浓度呈负相关,说明施氮处理较低的根源ABA浓度是导致其气孔导度较大的主要原因．     

Chemical signals and their regulations on the plant growth and water use efficiency of cotton seedlings under partial root-zone drying and different nitrogen applications

Partial root-zone drying during irrigation (PRD) has been shown effective in enhancing plant water use efficiency (WUE), however, the roles of chemical signals from root and shoot that are involved and the possible interactions affected by nitrogen nutrition are not clear. Pot-grown cotton (Gossypium spp.) seedlings were treated with three levels of N fertilization and PRD. The concentrations of nitrate (NO₃⁻), abscisic acid (ABA) and the pH value of leaf and root xylem saps, biomass and WUE were measured. Results showed that PRD plants produced larger biomass and higher WUE than non-PRD plants, with significant changes in leaf xylem ABA, leaf and root xylem NO₃⁻ concentrations and pH values, under heterogeneous soil moisture conditions. Simultaneously, high-N treated plants displayed larger changes in leaf xylem ABA and higher root xylem NO₃⁻ concentrations, than in the medium- or low-N treated plants. However, the WUE of plants in the low-N treatment was higher than that of those in the high- and medium-N treatments. PRD and nitrogen levels respectively induced signaling responses of ABA/NO₃⁻ and pH in leaf or root xylem to affect WUE and biomass under different watering levels, although significant interactions of PRD and nitrogen levels were found when these signal molecules responded to soil drying. We conclude that these signaling chemicals are regulated by interaction of PRD and nitrogen status to regulate stomatal behavior, either directly or indirectly, and thus increase PRD plant WUE under less irrigation.     

Hydraulic and chemical signalling in the control of stomatal conductance and transpiration.

Abscisic acid (ABA) transported in the xylem from root to shoot and perceived at the guard cell is now widely studied as an essential regulating factor in stomatal closure under drought stress. This provides the plant with a stomatal response mechanism in which water potential is perceived in the root as an indication of soil water status and available water resources. There is also ample evidence that stomata respond directly to some component of leaf water status. This provides additional information about water potential gradients developing between root and shoot as the result of water transport, allowing for a more stable regulation of shoot water status and better protection of the transport system itself. The precise location at which leaf water status is sensed, however, and the molecular events transducing this signal into a guard cell response are not yet known. Major questions therefore remain unanswered on how water stress signals perceived at root and leaf locations are integrated at the guard cell to control stomatal behaviour.     

Hormonal changes induced by partial rootzone drying of irrigated grapevine

Partial rootzone drying (PRD) is a new irrigation technique which improves the water use efficiency (by up to 50%) of wine grape production without significant crop reduction. The technique was developed on the basis of knowledge of the mechanisms controlling transpiration and requires that approximately half of the root system is always maintained in a dry or drying state while the remainder of the root system is irrigated. The wetted and dried sides of the root system are alternated on a 10-14 d cycle. Abscisic acid (ABA) concentration in the drying roots increases 10-fold, but ABA concentration in leaves of grapevines under PRD only increased by 60% compared with a fully irrigated control. Stomatal conductance of vines under PRD irrigation was significantly reduced when compared with vines receiving water to the entire root system. Grapevines from which water was withheld from the entire root system, on the other hand, show a similar reduction in stomatal conductance, but leaf ABA increased 5-fold compared with the fully irrigated control. PRD results in increased xylem sap ABA concentration and increased xylem sap pH, both of which are likely to result in a reduction in stomatal conductance. In addition, there was a reduction in zeatin and zeatin-riboside concentrations in roots, shoot tips and buds of 60, 50 and 70%, respectively, and this may contribute to the reduction in shoot growth and intensified apical dominance of vines under PRD irrigation. There is a nocturnal net flux of water from wetter roots to the roots in dry soil and this may assist in the distribution of chemical signals necessary to sustain the PRD effect. It was concluded that a major effect of PRD is the production of chemical signals in drying roots that are transported to the leaves where they bring about a reduction in stomatal conductance.     

Genotypic variation in 'early warning signals' from roots in drying soil: intrinsic differences in ABA synthesising capacity rather than root density determines total ABA 'message' in cowpea (Vigna unguiculata L.)

In a comparison of six cowpea cultivars, we determined the variation in abscisic acid (ABA) production as an ‘early warning signal’ produced in response to drought stress. By imposing drought only to the upper 20 cm rooting zone, we compared the rates of ABA synthesis relative to (i) total root mass and (ii) inherent variation per unit root mass. We were able to relate the intensity of the stress response to these two factors, and determine which is quantitatively more important as the primary signal indicating responsiveness to drought stress. Plants were grown in 1.2 m long columns and a soil drying treatment imposed in such a way that that upper roots were in dry soil and deep roots in soil at field capacity. Relative water contents (RWC) of stressed plants were similar and not significantly different from those of well watered controls. However, roots accumulated ABA in the dehydrated zone, where root water content ranged from 10–12 g g^?1 DW. The soil moisture contents and root ‐water contents in the dry zone were similar for each of the different varieties. However, the ABA contents were significantly different in drought‐stressed (upper) roots and ranged from 7.82 nmol g^?1 DW in cv. APC 689 to 16.02 nmol g^?1 DW in cv. APC 370, such that for varieties with similar overall root weights (e.g. APC 580 and APC 540) the different ABA contents were related to the capacity for ABA synthesis. The relationship between stomatal conductance and total root ABA was assessed, with a negative relation (r= 0.90, n= 24, P= 0.05) suggesting that the intrinsic capacity of cowpea varieties for ABA synthesis could play an important role in regulating stomatal conductance in a drying soil and provide useful selection criteria for tolerance to drought stress.     

Does engineering abscisic acid biosynthesis in Nicotiana plumbaginifolia modify stomatal response to drought?

The consequences of manipulating abscisic acid (ABA) biosynthesis rates on stomatal response to drought were analysed in wild‐type, a full‐deficient mutant and four under‐producing transgenic lines of N. plumbaginifolia. The roles of ABA, xylem sap pH and leaf water potential were investigated under four experimental conditions: feeding detached leaves with varying ABA concentration; injecting exogenous ABA into well‐watered plants; and withholding irrigation on pot‐grown plants, either intact or grafted onto tobacco. Changes in ABA synthesis abilities among lines did not affect stomatal sensitivity to ABA concentration in the leaf xylem sap ([ABA]_xyl), as evidenced with exogenous ABA supplies and natural increases of [ABA]_xyl in grafted plants subjected to drought. The ABA‐deficient mutant, which is uncultivable under normal evaporative demand, was grafted onto tobacco stock and then presented the same stomatal response to [ABA]_xyl as wild‐type and other lines. This reinforces the dominant role of ABA in controlling stomatal response to drought in N. plumbaginifolia whereas roles of leaf water potential and xylem sap pH were excluded under all studied conditions. However, when plants were submitted to soil drying onto their own roots, stomatal response to [ABA]_xyl slightly differed among lines. It is suggested, consistently with all the results, that an additional root signal of soil drying modulates stomatal response to [ABA]_xyl.