Correlation of cytokinins and abscisic acid with monocarpic senescence in soybeans1

Publisher Website
Google Scholar
Abstract
The involvement of cytokinins and abscisic acid (ABA) in the monocarpic senescence (foliar yellowing following fruit development) of soybeans was examined. Foliar sprays of cytokinin (10−4 M zeatin or 10−5 M benzyladenine), begun when the plants first set fruit and repeated every other day, significantly delayed, but did not prevent, monocarpic senescence. Foliar sprays of 10−4 M ABA, applied in the same manner, significantly hastened senescence of fruiting soybeans but apparently had no effect on depodded plants. Leaf and stem material from pre-senescent and senescent plants was extracted, chromatographed, and bioassayed for cytokinin-lilce activity (Amaranthus betacyanin production assay) and ABA-like activity (oat coleoptile straight growth assay for inhibitors). ABA-like activity increased, and cytokinin-like activity decreased in shoot tissue before the plants began to senesce. Cytokinin-like activity in the fruit also declined during this period. These results implicate a decrease in cytokinins and an increase in ABA-like inhibitors in the control of monocarpic senescence of soybeans, but neither alone is causal.