Abstract

In the cucumber cotyledon greening system, abscisic acid (ABA) is more potent inhibitor of growth and chlorophyll production and/or destruction than methyl jasmonate (MJ). The inhibitory effect of ABA is apparent within 5 h of exposure to light whereas MJ is ineffective at all concentrations tested (10−6 to 10−3M). With longer exposure of 24 h to light and in the presence of 40 mM KC1, the inhibition of growth and chlorophyll production by ABA is more pronounced whereas MJ does not inhibit growth and inhibits chlorophyll levels only at the higher concentrations. Both benzyladenine and KC1 stimulate chlorophyll production and increase the fresh weights of the cucumber cotyledons and either one of these compounds reverse the inhibitory effects of ABA. Inhibition of chlorophyll production by ABA is valuable as a simple and rapid bioassay for abscisic acid. Under similar conditions cytokinins increase chlorophyll production and hence the cucumber cotyledon greening system is ideal for detecting both ABA which inhibits and cytokinins which stimulate chlorophyll production.

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