Endogenous factors controlling monocarpic senescence in wheat plants

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Monocarpic senescence is known to be induced by flowering and/or fruiting, indicating that fruit plays an crucial role in the senescence. Commencement of the senescence of a plant seems to be controlled by a balance between the lovel of cytokinins that inhibit the senescence and the levels of compounds that stimulate the process, such as abscisic acid (ABA) and jasmonic acid (JA). The level of cytokinins in flag leaves in senescent plants was higher than those in plants before heading, indicating that deficiency of cytokinins is not involved in the senescence. The levels of ABA,JA and its methyl ester (JA-Me) in ears were very low at any time of the development of ears, suggesting that these compounds are not involved in the senescence.Chlorophyll retention test which was carried out by the first leaves of wheat showed the presence of strong senescence-promoting activity in the hexane-soluble fraction obtained from the ears. The maximum activity was found in the ears at late milk-ripe stage, suggesting that the senescence promoting compound is responsible for the commencement of the monocarpic senescence. Chromatographic behavior of the active compound was different from those of ABA,JA and JA-Me. The compound has no UV absorption. Purification and identification of the compound are now in progress.