Leaf Senescence and Abscisic Acid in Leaves of Field-grown Soybean

Leaf senescence in field-grown soybean (Merrill) as defined by the period after full expansion, was studied by measuring abscisic acid (ABA), total soluble protein, and chlorophyll in leaves through the later part of the growing season. ABA concentrations increased significantly at the end of the season when leaves had started to turn yellow, well after total soluble protein and chlorophyll had started to decline. The results indicate that events occurring before leaf yellowing are more significant in evaluating leaf senescence since the yellowing condition and rise in ABA are effects of changes in physiological activity beginning when leaves are still green.     

Interrelations between Gibberellic Acid, Cytokinins and Abscisic Acid in Retarding Leaf Senescence

The interrelation between the effects of abscisic acid (ABA) and the effects of cytokinins and gibberellic acid in retarding leaf senescence was investigated. Leaf discs from plants of Taraxacum megallorrhizon, Rumex pulcber and Tropaeolum majus were floated on solutions of cytokinin or GA to which given amounts of ABA were added. After five days, chlorophyll was extracted and the amount estimated spectrophoto-metrically. The interrelation between the effects of abscisic acid and cytokinins differed from that between the effects of ABA and gibberellic acid. Abscisic acid reduced the senescence retarding effect of GA more than that of cytokinins. A high concentration of cytokinins nullified the senescence enhancing effect of low concentrations of ABA. GA did not reverse the effects of ABA.     

Effects of Abscisic Acid and Water Stress on the Senescence of Detached Rice Leaves

The effects of abscisic acid (ABA) and water stress on senescence and enzyme activities of oxygen scavenging enzymes of detached rice leaves were compared. Exogenously applied ABA exhibited water stress-like effects by promoting senescence, by decreasing the activities of catalase, peroxidase, ascorbate peroxidase and superoxide dismutase. It seems that the effects of water stress on senescence and enzyme activities are possibly mediated through increased content of endogenous ABA. This revised version was published online in July 2006 with corrections to the Cover Date.     

Control of Ribonuclease and Acid Phosphatase by Auxin and Abscisic Acid during Senescence of Rhoeo Leaf Sections

We report the effects of abscisic acid and auxin (α-naphthalene acetic acid) on regulation of enzyme synthesis during senescence of leaf sections of Rhoeo discolor Hance. Abscisic acid always accelerates the onset of and enhances the magnitude of the increase in activity of acid phosphatase; this is followed by an acceleration of the onset of a rapid increase in free space.     

外源施加AsA和MeJA对乙烯利诱导水稻叶片衰老的影响

以野生型水稻(Oryza sativa)株系中花11(ZH-11)及其抗坏血酸合成关键酶基因GLDH下调株系(GI-2)为材料,研究了外源抗坏血酸(AsA)与茉莉酸甲酯(MeJA)对乙烯利诱导下水稻叶片早衰现象的影响。结果表明,外源AsA提高了水稻GI-2中的抗坏血酸含量、Rubisco含量及叶绿素的含量,减缓了其光合特性参数的下降速率,但对水稻ZH-11没有显著影响。外源MeJA降低了两株系的抗坏血酸、Rubisco及叶绿素含量,加快了叶内光合特性参数的下降速率,且对ZH-11的影响大于GI-2。因此,外源AsA处理能有效缓解乙烯利诱导的水稻叶片早衰现象,使叶片的衰老进程得以延缓,而外源MeJA作用相反。     

The Effect of Light and Hormones on Leaf Senescence

With wheat leaves as material, the changes of superoxide dismutase (SOD), lipid peroxi-dation and membrane permeability during leaf senescence in light or dark, and treated withphytohormones (KT or ABA) have been studied. The changes of chlorophyll content, lipidperoxidation and fine structure of spinach chloroplasts senescing in light or dark have alsobeen studied. When leaves senesce in light, the activity of SOD increased at first then decreased. The increase of SOD activity was able to result from the synthesis of new protein. Lightwas found to delay the leaf senescence obviously but also accelerate leaf senescence by causinglipid peroxidation when prolonged the illumination time. The delay or acceleration of leafsenescence by exogenous hormones were observed, it may be due to the control of lipid peroxi-dation by adjusting the activity of SOD. O2-participated the chlorophyll decomposition andlipid peroxidation during chloroplasts senesce in light. A favourable role of light in mainta-lng the fine structure of isolated chloroplasts was clear.     

Abscisic Acid and Water Relations of Rice (Oryza sativa L.): Effects of Drought Conditioning on Abscisic Acid Accumulation in the Leaf and Stomatal Response

The effects of a period of water stress (drought conditioning)on responses to a second (challenge) stress were examined inyoung vegetative rice (Oryza sativa L.) plants. Drought conditioningdid not affect the rate of subsequent stress development, nor,in a first experiment, did it influence relations between turgor(_p) and total () leaf water potential. However, conditioningdid extend the range of _p over which stomata remained open andsignificantly reduced the amount of ABA which accumulated inthe leaf at a given _p. The change in stomatal behaviour (stomataladjustment) was quantitatively accounted for by the change inleaf ABA accumulation. The reduction in ABA accumulation due to conditioning did notinvolve a change in the potential capacity to produce ABA, asABA accumulation in partially dehydrated detached leaves wasnot reduced by conditioning. It is suggested that effects ofconditioning on leaf ABA content in the intact plant involvechanges in the rate of ABA export from the leaf. Oryza sativa L, rice, drought conditioning, stomata, water stress, abscisic acid     

Effects of Cycloheximide and Light on Leaf Senescence in Maize and Hydrangea

The senescence of maize and hydrangea leaves after detachmentand darkening was studied in terms of the loss of chlorophylland protein. Chlorophyll contents of the detached leaves decreasedin the dark in both plants. Cycloheximide at 0.1 mM effectivelyinhibited the loss of chlorophyll in maize, but did not do soin hydrangea. Continuous irradiation with white light of 4.6Wm^–2 prevented the loss of chlorophyll in hydrangea leaves,while it caused bleaching of maize leaves. Reducing agents suchas ascorbic acid and glutathione did not prevent the bleachingby light. In maize leaves, the amount of protein decreased inthe dark more slowly than that of chlorophyll, and cycloheximideslightly prevented the protein decrease. Continuous light irradiationof 4.6 Wm^–2 delayed the loss of protein more effectivelythan cycloheximide did. (Received January 31, 1981; Accepted May 21, 1981)     

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.     

Retardation of Leaf Senescence by Ascorbic Acid

Leaf discs of Solatium melongena were floated on various concentrationsof ascorbic acid (AA), gibberellic acid (GA₃), and kinetin inorder to study their effect on senescence. AA was highly effectivein retarding senescence as shown by the arrest of the fall inlevels of chlorophyll, DNA, RNA, and proteins. AA was effectiveat a lower concentration than that of GA₃ or kinetin.     

Inhibition of Light-Stimulated Leaf Expansion by Abscisic Acid

Abscisic acid (ABA) applied to intact bean (Phaseolus vulgaris)leaves or to isolated leaf discs inhibits light-stimulated cellenlargement This effect may be obtained with 10^–4 molm^–3 ABA, but is more significant at higher concentrations.The inhibition of disc expansion by ABA is greater for discsprovided with an external supply of sucrose than for discs providedwith KC1, and may be completely overcome by increasing the KC1concentration externally to 50 mol m^–3. Decreased growthrate of ABA-treated tissue is not correlated with loss of solutesfrom growing cells, but is correlated with a decrease in cellwall extensibility. ABA does not prevent light-stimulated acidificationof the leaf surface, and stimulates the acidification of theexternal solution by leaf pieces. However, the capacity of thecell walls to undergo acid-induced wall loosening is diminishedby ABA-treatment. The possibility that ABA acts directly byinhibiting growth processes at the cellular level, or indirectlyby causing stomatal closure, is discussed. Key words: Phaseolus vulgaris, ABA, Inhibition, Leaf expansion     

Combined Effects of Abscisic Acid and Sucrose on Growth and Senescence of Rose Flowers

The effects of sucrose and abscisic acid (ABA) and their interaction on development and senescence of petals were studied with leafless roses cultivar Super Star. Sucrose and ABA had opposing effects on the cut flowers. Sucrose retarded and ABA promoted processes associated with senescence: wilting, increase in pH, “blueing” and decrease in protein content of petals. These opposing effects are mutually antagonized when both chemicals are applied. ABA applied to flowers cut at the bud stage, promoted the rate of petal growth (but not their final size), increased respiration and caused a decrease in sucrose and an increase in level of reducing sugars. It is suggested that one way by which ABA accelerates senescence of cut roses is by promoting petal growth and respiration, thus decreasing the carbohydrate level in the petals and triggering the chain of metabolic processes leading to aging.     

水稻叶片衰老相关基因的研究进展

水稻叶片的衰老是制约杂交稻产量提高的主要因素之一,有数据表明水稻籽粒灌浆所需营养物质的60%～80%来自叶片的光合作用,实践证明叶片每推迟1天衰老,产量可提高产1%左右.因此,对叶片衰老的形态、生理生化及其相关分子机理等进行研究具有重要的现实意义.近年来水稻叶片衰老的相关研究表明,叶片的衰老是一个受众多因素影响的复杂过程,在这个过程中叶片发生了巨大的形态与生理生化变化,而这些变化均离不开基因的调控作用.大量实验结果表明:在衰老过程中,叶片细胞有选择地启动或增强某些基因(叶片衰老相关基因)的表达,而关闭或减弱另一些基因(衰老下调基因)的表达,由此来调控叶片衰老的进程.目前研究者已在研究衰老突变体等相关的材料中发现了许多与水稻叶片衰老有关的基因.本文重点概述了近年来水稻叶片衰老相关基因的研究状况,并对未来研究方向等问题做了思考与探讨,以期能为开展进一步的研究工作提供参考.     

Modification of Leaf Size in Rice (Oryza sativa L.) and its Effects on Water Stress-induced Abscisic Acid Accumulation

The ability of detached leaves of the rice cultivars IR20 and63–83 and their F₂ progeny to accumulate ABA in responseto water stress is negatively correlated with leaf size. Itwas shown that this association was not an artifact of incubationconditions following the imposition of stress. Also, it waspossible to break the correlation by selecting plants in segregatingpopulations which differed in ABA yet had similar leaf size. In further experiments, leaf size was altered phenotypicallyby various treatments; either being increased by gibberellinapplication or periodic removal of tillers, or reduced by priorexposure to water stress or ABA. Although responses to thesetreatments were complex, the results demonstrated that leafsize and accumulation capacity were at least partially independent.It is suggested that the correlations observed previously inF₂ populations from the cross IR20 x 63–83 were a resultof genetic linkage. Oryza saliva L., rice, leaf size, abscisic acid, water stress     

Effects of Abscisic Acid in Senescence of Garlic Al1tium sativura Scape

Removing the apical cloves from the excised garlic scapes could delay the senescence of scape and decrease the rate of dry matter loss during storage. The ABA content of all the portions of the scapes with apical cloves is decreased as the prolongation of storage period; but its content of all the portions of the scapes with the cloves reaches their peak one after another within the first 6 days of the experiment period. The peak of ABA in the apical cloves appears earliest; the ABA content of any portion of the scapes is lower than that of the cloves, and gradually decreases from upper to lower portions, and the peak of ABA content appears in the sequence as above. Exogenous ABA which is added to the top of the scapes without cloves would simulate the function of the apical cloves in part and accelerates the chlorophyll destruction and senescence of the scapes. No ethylene can be detected by the G. C., in the process of senescence. The authors suggest that ABA is mainly synthesized in the cloves, and then transported into the scapes from there. In the senescence of garlic scapes and in the redistribution of material between the apical cloves and the scapes (the relation between the sink and source), ABA functions as transporting information and promoting senescence but ethylene has not such a function. The senescence of garlic scape could be divided into two stages: first the static phase and second, the active phase.     

Effects of Abscisic Acid on Senescence, Permeability and Ribosomal Patterns in Mimosa Hypocotyl Callus Tissue

Abscisie acid effects on ³²P uptake, polysomal patterns and senescence in mimosa (Albizzia julibrissin Durazzini) hypocotyl callus tissues were compared. Incubation of hypocotyl callus tissue with, abscisic acid for 4.5 h significantly decreased tissue uptake of ³²P, and quantitatively, but not significantly, decreased incorporation of ³²P into ribosomal fractions after adjusting for uptake. Abscisic acid accelerated senescence in the callus tissues. Abscisic acid inhibition of ³²P uptake is presented as a possible source of misinterpretation of ribosomal ³²P incorporation data.     

水稻叶片早衰成因及分子机理研究进展

植物叶片衰老是叶片发育的最终阶段,也是植物在长期进化过程中形成的适应性机制。水稻(Oryza sativa)叶片的衰老对其产量和品质影响极大,相关研究主要集中在早衰。该文综述了水稻早衰及其调控基因的研究进展,尤其对水稻叶片早衰的形成原因、发生过程、生理变化及防治措施进行了阐述,以期为深入解析水稻早衰的分子机制奠定理论基础,同时为水稻育种提供参考。     

The Intracellular Location of Abscisic Acid in Stressed and Non-Stressed Leaf Tissue

The intra-cellular location of ABA was investigated in relation to its sites of synthesis. Chloroplasts were isolated from stressed and non-stressed spinach leaves and their ABA content determined. Virtually all of the ABA from non-stressed leaves was contained in the chloroplasts compared with only a small fraction of ABA isolated from stressed leaves. Chloroplasts prepared from turgid leaves and subsequently lysed in vitro retained most of their ABA and phaseic acid (PA) complement but this was removed with organic solvents. While the possibility of extra-chloroplastic synthesis cannot be discounted the data indicate that stress-induced ABA synthesis occurs in the chloroplast and that the ABA readily migrates from there to other parts of the plant.