脱落酸在植物花发育过程中的作用

植物激素脱落酸(ABA)对植物的生长发育具有多方面的调节作用,比如种子休眠、萌发,营养生长,环境胁迫反应等。大量研究显示,ABA也参与了植物的成花调控。影响植物成花调控的环境因子,包括光周期变化、春化作用、干旱等均会导致植物体内ABA代谢的变化。本文从调控植物开花的4条主要途径与植物体内ABA代谢变化之间的相互关系,花芽分化时期ABA在植物叶芽和花芽中的动态分布以及离体培养条件下ABA对花芽分化的影响等方面总结了ABA与植物花发育这一领域的最新研究进展。对ABA在植物成花诱导和花发育中的作用进行了综合分析。     

Role of Abscisic Acid in Seed Dormancy

Seed dormancy is an adaptive trait that improves survival of the next generation by optimizing the distribution of germination over time. The agricultural and forest industries rely on seeds that exhibit high rates of germination and vigorous, synchronous growth after germination; hence dormancy is sometimes considered an undesirable trait. The forest industry encounters problems with the pronounced dormancy of some conifer seeds, a feature that can lead to non-uniform germination and poor seedling vigor. In cereal crops, an optimum balance is most sought after; some dormancy at harvest is favored because it prevents germination of the physiologically mature grain in the head prior to harvest (that is, preharvest sprouting), a phenomenon that leads to considerable damage to grain quality and is especially prominent in cool moist environments. The sesquiterpene abscisic acid (ABA) regulates key events during seed formation, such as the deposition of storage reserves, prevention of precocious germination, acquisition of desiccation tolerance, and induction of primary dormancy. Its regulatory role is achieved in part by cross-talk with other hormones and their associated signaling networks, via mechanisms that are largely unknown. Quantitative genetics and functional genomics approaches will contribute to the elucidation of genes and proteins that control seed dormancy and germination, including components of the ABA signal transduction pathway. Dynamic changes in ABA biosynthesis and catabolism elicit hormone-signaling changes that affect downstream gene expression and thereby regulate critical checkpoints at the transitions from dormancy to germination and from germination to growth. Some of the recent developments in these areas are discussed.     

Plant Cold Acclimation: The Role of Abscisic Acid

The freezing tolerance or cold acclimation of plants is enhanced over a period of time by temperatures below 10°C and by a short photoperiod in certain species of trees and grasses. During this process, freezing tolerance increases 2–8°C in spring annuals, 10–30°C in winter annuals, and 20–200°C in tree species. Gene upregulation and downregulation have been demonstrated to be involved in response to environmental cues such as low temperature. Evidence suggests ABA can substitute for the low temperature stimulus, provided there is also an adequate supply of sugars. Evidence also suggests there may be ABA-dependent and ABA-independent pathways involved in the acclimation process. This review summarizes the role of ABA in cold acclimation from both a historical and recent perspective. It is concluded that it is highly unlikely that ABA regulates all the genes associated with cold acclimation; however, it definitely regulates many of the genes associated with an increase in freezing tolerance.     

The Role of Abscisic Acid in Flower Abscission of Lupinus luteus

The role of abscisic acid in the control of flower abscission in Lupinus luteus L. was examined. Using a modified extraction and purification technique, endogenous abscisic acid levels in the upper flowers of an inflorescence were found to increase markedly some days before abscission could be detected. When abscisic acid was injected into flower-bearing nodes or fed via the roots, no increase in the abscission rate was obtained at any position in the flowerhead. Application of abscisic acid to only the leaves resulted in a marked increase in flower abscission. The role of abscisic acid per se as a primary controlling factor of flower abscission in yellow lupin is questioned.     

The Role of Abscisic Acid in Senescence of Detached Tobacco Leaves

The role of abscisic acid in the regulation of senescence was investigated in detached tobacco leaves (Nicotiana rustica L.). Leaves senesced in darkness showed a sharp rise in abscisic acid level in the early stage of aging, followed by a rapid decline later. The same trend was found when leaves were aged in light, but the rise in abscisic acid occurred four days later than in darkness. Senescence was slower in light than in darkness, while salt stress accelerated the processes. Leaves treated with kinetin which senesced in light and darkness, did not show an increase in abscisic acid. Application of kinetin led to a transformation from free to bound ABA. These results may indicate that ABA and cytokinin are involved in a trigger mechanism which regulates senescence; the stage at which this trigger is activated determines the rate of senescence.     

Role of Abscisic Acid in Thermal Acclimation of Plants

Abscisic acid (ABA) is a stress hormone that confers resistance to abiotic stressors, including drought, salt, cold, and heat. In general, antioxidant capacity and heat shock proteins (HSPs) mainly mediate ABA to enhance thermal acclimation in plants, but sugar metabolism and signaling also play critical roles in this response in the presence of ABA. Indeed, ABA accelerates sugar metabolism and transports more carbohydrates to spikelets under heat stress, which is beneficial to plants surviving under stressful conditions. Few studies have summarized the interactions among sucrose metabolism, signaling, and hormones in plants during heat stress, but this topic will likely attract more attention in the future. This article reviews the antioxidant capacity, HSPs, sugar metabolism, hormone crosstalk, and their interactions involved in ABA-induced heat tolerance in plants. Clarifying the underlying mechanisms will be invaluable for breeding heat-resistant cultivars and for developing new tissue culture techniques that reduce heat damage in plants.     

逆境胁迫下植物体内脱落酸的生理功能和作用机制

文章介绍逆境胁迫下植物体内ABA的生理功能和作用机制研究进展。     

The Role of Endogenous Abscisic Acid in the Response of Plants to Stress

When a continuous stream of warm air (38°C) was directedon to the leaves of dwarf bean seedlings they wilted and thengradually regained turgor. This process of adaptation was accompaniedby an increasing abscisic acid (ABA) level in the leaves andan increase in leaf resistance (R_L). It is suggested that theleaf-water deficit induced by the warm-air treatment causedthe increase in ABA level and that the latter was responsiblefor stimulating stomatal closure, enabling the plants to regainfull turgor. A similar type of adaptation, brought about byan increased level of ABA in the leaves, is believed to occurin tomato, dwarf bean, and wheat plants when they are flooded.Predictably, in rice, a species adapted to a flooded environment,seedlings showed no increase in ABA level as a result of flooding. It is proposed that adaptation may involve the formation ofan equilibrium between ABA and its conjugate form (i. e. theglucose ester). The ABA-conjugate was observed to disperse slowlyfrom leaves recovering from a water deficit and therefore itmay act as a metabolic ‘back-stop’, enabling the‘free’ ABA level to remain high for a period evenwhen the leaves have regained turgor. Abscisic acid appears to be responsible for alleviating theeffects of water stress in plants, making it possible for plantsto pass through periods of stress with little harm.     

Potential Role of Abscisic Acid in Cotton Fiber and Ovule Development

Fibers and ovules of a cotton cultivar (Gossypium hirsutum L. Trambak-108) were analyzed for growth and free abscisic acid (ABA) content by indirect enzyme immunoassay. An inverse correlation between fiber elongation and ABA content was observed. In the seed, accumulation of ABA was observed during secondary thickening and the maturation phase. The potential role of ABA in fiber and seed development is discussed. Received June 25, 1997; accepted October 15, 1997     

Physiological and Biochemical Mechanisms Involved in the Response to Abscisic Acid in Maize Coleoptiles

The role of abscisic acid (ABA) in controlling growth and developmenthas been studied in maize (Zea mays L.) coleoptile segments.Application of ABA reduces the elongation rate by about 50%and affects ion fluxes. In particular, proton extrusion is decreasedwhile potassium efflux is greatly enhanced. Apparently, ABAdoes not: seem to influence calcium influx from the apoplastinto the cytosol, but more likely it influences its efflux.Alteration of cytosolic calcium concentration may also be obtainedby increasing its release from internal stores. This possibilitymight be sustained by the increased hydrolysis of phosphatidylinositolupon ABA application. Change in the balance of ion fluxes shouldresult from regulation of transport mechanisms at the membranelevel and should produce changes in the transmembrane electricalpotential. The H⁺- ATPase and the ATP-dependent calcium transportactivities are both influenced by the treatment with ABA, –55%and –40%, respectively. Under these conditions [Ca²⁺]_cytand pH_cyt can be modified and, as a consequence of their regulation,they may play an important role in mediating the physiologicaland biochemical effects of ABA, acting as second intracellularmessengers. ¹Research supported by National Research Council of Italy, SpecialProject RAISA, Sub-Project N. 2, Paper n. 2782.     

The Role of Abscisic Acid in Acclimation of Plants Cultivated in vitro to ex vitro Conditions

The content of endogenous free abscisic acid (ABA) in the shoots of in vitro cultivated tobacco (Nicotiana tabacum L. cv. White Burley) and its changes during ex vitro acclimation of these plants to the greenhouse or growth chamber were estimated. The content of free ABA significantly increased at the 1^st and/or 2^nd day after plant transfer from in vitro to ex vitro. The ABA content of plants covered with transparent foil to maintain higher relative humidity (RH), did not significantly differ from ABA content of plants cultivated under ambient RH. Transfer to fresh medium also transiently increased the content of endogenous ABA. The ABA content in plants, which had been acclimated for 1 week to ex vitro conditions, decreased to the content found in the in vitro plants. Acclimation to ex vitro conditions affected the stomata on adaxial and abaxial sides differently: stomata on the adaxial side were less open than those on the abaxial one. The exogenous application of 5 μM ABA increased transiently its endogenous concentration in shoots of in vitro plants more than ten fold, but after 1 week the concentration in the shoots decreased. This revised version was published online in July 2006 with corrections to the Cover Date.     

长期喷施ABA对云杉幼苗生长和生理特性的影响

采用单因素盆栽实验,通过叶面喷施5、10、15和20mg·L^-1 4个浓度的ABA溶液,研究了长期外源ABA处理对云杉（Piceaasperata）幼苗生长及生理特性的影响。5年的研究结果表明：长期不同浓度ABA处理显著影响了云杉幼苗的多种生长及生理生化指标。当ABA浓度为5、10和15mg·L^-1叫时有利于云杉幼苗根重、茎重和总生物量的积累,并且提高了叶片中可溶性蛋白和脯氨酸的含量,降低了MDA含量：20mg·L^-1 ABA处理使幼苗的叶重、总生物量、脯氨酸及可溶性糖含量显著下降,明显增加了叶片中MDA含量。此外,各浓度ABA处理均显著降低了云杉幼苗的株高、叶绿素含量以及SOD和APX活性。本研究结果显示,长期ABA处理对云杉幼苗生长和生理特性的影响与所喷施的ABA浓度有关,长期高浓度ABA（20mg·L^-1）处理不利于云杉幼苗生长。     

The Selective Effect of Abscisic Acid on Ribonucleic Acid Components

As determined by methylated albumin kieselguhr (MAK) fractionation, GA₃ (gibberellic acid) significantly increased and ABA (abscisic acid) decreased RNA levels. In the case of ABA this effect was selective, the ribosomal RNA manifesting the typical decrease; while the sRNA peak was markedly increased. The pattern of labelled uridine incorporation into RNA resembles the MAK absorbancy profile and here as well, ABA although causing an overall decrease, increases labelling in the sRNA peak. The results are interpreted as a possible selective effect of ABA or alternatively as an accumulation in the sRNA peak of rRNA breakdown products. From in vitro experiments it was furthermore evident that ABA mediated RNA hydrolysis probably does not involve a direct activation of RNase by ABA. The in vivo effect would probably be devious.     

Role of Abscisic Acid in Water Stress-induced Antioxidant Defense in Leaves of Maize Seedlings

Roles of abscisic acid (ABA) in water stress-induced oxidative stress were investigated in leaves of maize ( Zea mays L.) seedlings exposed to water stress induced by polyethylene glycol (PEG 6000). Treatment with PEG at &#109 0.7 MPa for 12 and 24 h led to a reduction in leaf relative water content (RWC) by 7.8 and 14.1%, respectively. Duration of the osmotic treatments is considered as mild and moderate water stress. The mild water stress caused significant increases in the generation of superoxide radical ( O 2 &#109 ) and hydrogen peroxide (H 2 O 2 ), the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) and the contents of ascorbate (ASC), reduced glutathione (GSH). The moderate water stress failed to further enhance the capacity of antioxidant defense systems, as compared to the mild water stress. The contents of catalytic Fe, which is critical for H 2 O 2 -dependent hydroxyl radical ( &#148 OH) production, and the oxidized forms of ascorbate and glutathione pools, dehydroascorbate (DHA) and oxidized glutathione (GSSG), markedly increased, a significant oxidative damage to lipids and proteins took place under the moderate water stress. Pretreatment with ABA caused an obvious reduction in the content of catalytic Fe and significant increases in the activities of antioxidant enzymes and the contents of non-enzymatic antioxidants, and then significantly reduced the contents of DHA and GSSG and the degrees of oxidative damage in leaves exposed to the moderate water stress. Pretreatment with an ABA biosynthesis inhibitor, tungstate, significantly suppressed the accumulation of ABA induced by water stress, reduced the enhancement in the capacity of antioxidant defense systems, and resulted in an increase in catalytic Fe, DHA and GSSG, and oxidative damage in the water-stressed leaves. These effects were completely prevented by addition of ABA, which raised the internal ABA content. Our data indicate that ABA plays an important role in water stress-induced antioxidant defense against oxidative stress.     

The Role of Gibberellin, Abscisic Acid, and Auxin in the Regulation of Developing Wheat Grains

Three forms of inhibition of germination of developing wheatgrains are described. One, due to the outer pericarp, may notinvolve growth substances. The others occur in the embryo itselfand are due also to the other grain tissues surrounding theembryo. Experiments with applied growth substances suggest thatthese may be regulated by a balance of endogenous gibberellinsand abscisic acid, but the results of extraction experimentsshow limited correlation with germination experiments, and indicatethat auxin may also be inhibitory.