Inhibition by Calcium of Senescence of Detached Cucumber Cotyledons

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Abstract
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 CaCl2 exhibited reduced chlorophyll loss and H2O2 production, reduced and delayed ethylene production, and did not undergo a burst in CO2 production. In contrast, Mg had little effect on cotyledon senescence, whereas K stimulated chlorophyll loss but did not increase H2O2 accumulation of ethylene and CO2 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 H2O2 to the solutions on which cotyledons were floated stimulated chlorophyll breakdown, but effects on ethylene and CO2 were not consistent.