Changes in endogenous growth regulators in nasturtium leaves during senescence.

By use of lettuce-hypocotyl and wheat-coleoptile bioassay, the presence of both gibberellin (GA)-like and abscisic-acid(ABA)-like components in acidic ethyl-acetate extracts of fully expanded nasturtium (Tropaeolum majus) leaves has been shown. During senescence of detached leaves there was a progressive decline in GA-like components and an increase in ABA-like components. Pretreatment of detached leaves with GA3 or kinetin prevented changes in the levels of endogenous growth regulators and delayed senescence. The observations provide experimental verification for the concept that senescence is associated with changes in endogenous growth regulators.