The interaction of hormonal and environmental factors in leaf senescence |
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Authors: | K V Thimann |
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Institution: | (1) The Thimann Laboratories, University of California, 95064 Santa Cruz, CA, USA |
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Abstract: | The work concerns the senescence of isolated young leaves of oats (Avena sativa) floated on water or solutions. Senescence is rapid in darkness but slow in white light; the effect of light is not due to
photosynthesis, but is paralleled by stomatal opening. Closure of the stomata by osmotic or chemical means makes senescence
in light proceed as fast as in darkness, while opening the stomata in darkness by cytokinins, fusicoccin,etc., delays senescence to rates typical of light. The osmotic closure in light is mediated by abscisic acid, and since this also
accumulates in darkness it appears as a major factor controlling senescence. Efflux of ions into the solution; indicating
increased permeability, occurs almost in parallel with senescence. Senescence in light is accelerated by 1-aminocyclopropane-l-carboxylic
acid (ACC) and inhibited by cobalt, silver or aminoethoxyvinyl glycine (AVG) which interfere with ethylene production or action;
however, ethylene’s role is unclear because some reagents, including kinetin, that delay senescence, actually increase ethylene
production. At the endogenous level, therefore, ethylene may not be a limiting factor. Finally, a new ethylene-generating
system is described in which the dehydrogenation of linoleic acid is coupled through manganese to the oxidation of ACC; it
is probably activein vivo. |
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