The Influence of Aliphatic Alcohols on Leaf Senescence

Abstract

Because of the effects of ethanol used as a solvent in other experiments, the action of aliphatic alcohols on leaf senescence in the dark has been studied systematically. These compounds both maintain chlorophyll and prevent proteolysis in the dark, much as do the cytokinins and other senescence-delaying substances. The activity of the straight-chain alcohols increases in a log-linear fashion with increasing chain length up to 1-octanol. Introduction of a branch in the chain or of a second OH group greatly decreases, or in some cases annuls, the antisenescence activity. In all cases, the action on senescence is closely (although not always exactly) paralleled by opening of the stomata. Abscisic acid and exposure to high concentrations of osmoticum, both of which close the stomata, antagonize the action of the alcohols. Some interactions with other agents are noted. The effects are compared with reported effects on seed germination, on hemolysis and animal membranes, and especially on permeability to K' ions, and a tentative basis for the mechanism of action is advanced.The ability of a number of chemically unrelated compounds to exert striking modifications of the progress of senescence in the detached leaves of oat seedlings has been reported elsewhere (22,24, and literature cited therein). Besides the cytokinins, at least five different compounds act to delay senescence in the dark, whereas three, as well as two physical treatments, promote the slower rate of senescence in the light, thus antagonizing the delaying effect of light. We found that in all cases the action on senescence was paralleled by an action on the stomatal aperture; stomatal closure paralleled promotion of senescence and stomatal opening paralleled its delay or inhibition.In studying these effects, it was necessary on several occasions to use alcohol as a solvent. Although the ethanol was diluted down to a maximum of 1% before application of the solution to the leaves, we noted that controls floated on this aqueous alcohol in darkness behaved very differently from those floated on H20. An example, with two concentrations of ethanol, is shown in Table I. Figures I and 2 of reference 24 also showed alcohol effects, but these were superimposed on the effects of FC2. It is clear from these data that ethanol exerts an effect on senescence in darkness like that of the several senescence inhibitors, although more weakly. Repeated observations of this alcohol effect led to a study of the action of a number of aliphatic alcohols on senescence. In this paper we report the considerable activity of a series of aliphatic alcohols in preventing or delaying leaf senescence in the dark. Disappearance of Chl and proteolysis responded similarly in all cases examined. The relation between structure and activity 'This work was supported in part by Grant BMS 7683126 from the National Science Foundation (to K. V. T.).2 Abbreviations: FC: fusicoccin; CCCP: carbonyl cyanide m-chlorophenylhydrazone. among the alcohols is closely parallel to reported effects...

Cytokinin Modification of Mitochondrial Function

“…If cytokinin action in the mitochondria is important to plant growth and development, one might anticipate that some of these compounds could produce 'cytokinin' effects. In this regard, it is interesting that certain alcohols delay leaf senescence and so do cytokinins (10). However, we failed to observe stimulation of cell division in soybean tissue cultures when we tested a number of the compounds (to be reported elsewhere).…”

Benzothiazole derivatives substituted in position 2 as biologically active substances with plant growth regulation activity

“…Visibly, they turn yellow or lose their color. This is a consequence of the deg- radation of chlorophyll and proteins and can be retarded, to some extent, if the excised leaves are treated with cytokinins (Richmond and Lang 1957), or substances with anti senescence effects (Satler and Thimann 1980, Thomas and Katterman 1986, Cavender et al 1988. Significantly cytokinin-like activity manifested solely by derivate No.…”

Relation between Respiration and Senescence in Oat Leaves

“…The gradual overall respiratory rise parallels the slow Chl disap- In tissues whose respiratory systems are insensitive to cyanide, it is commonly found that they are sensitive to hydroxamic acids such as SHAM or CLAM (18). For our purpose, SHAM was unsuitable as an inhibitor because its low water solubility requires the use of alcoholic solutions, which themselves exert powerful effects on senescence (16). Potassium benzyl hydroxamate, BAM, is water-soluble up to above 100 mm and was therefore adopted.…”