Inhibition by calcium of senescence of detached cucumber cotyledons: effect on ethylene and hydroperoxide production.

The effect of Ca on senescence was followed in detached cucumber (Cucumis sativus L.) cotyledons floating on various solutions in the dark. Compared with those in water, cotyledons in 10(-4) molar CaCl(2) exhibited reduced chlorophyll loss and H(2)O(2) production, reduced and delayed ethylene production, and did not undergo a burst in CO(2) production. In contrast, Mg had little effect on cotyledon senescence, whereas K stimulated chlorophyll loss but did not increase H(2)O(2) accumulation of ethylene and CO(2) production. This reduction in the rate of senescence by Ca could also be achieved by increasing the endogenous levels of Ca in the cotyledons before excision, although the reduction was less than that with Ca in the external solution. The addition of H(2)O(2) to the solutions on which cotyledons were floated stimulated chlorophyll breakdown, but effects on ethylene and CO(2) were not consistent.