Differential effects of methyl jasmonate on growth and division of etiolated zucchini cotyledons

The jasmonates are well studied in the context of plant defence but increasingly are also recognised as playing roles in development. In many systems, jasmonates antagonise the effects of cytokinins. The aim of the present work was to elucidate interactions between methyl jasmonate and cytokinin (benzyladenine) in regulating growth of zucchini (Cucurbita pepo L., cv. Cocozelle, var. Tripolis) cotyledons, taking advantage of the ability to simultaneously quantify cell enlargement and division from paradermal sections of the first palisade layer. Growth regulators were applied to cotyledons, excised from dry seeds and grown in darkness. Cytokinin stimulated expansion and division whereas, surprisingly, jasmonate stimulated expansion but inhibited division. Jasmonate antagonised the stimulating effect of cytokinin on division but worked cooperatively with cytokinin in increasing expansion. However, expansion with jasmonate was more isotropic than with cytokinin. Jasmonate also stimulated the loss of cellular inclusions and soluble protein. Soluble proteins revealed a partial antagonism between jasmonate and cytokinin. These results illustrate the complex interplay between jasmonates and cytokinin in the regulatory network of cotyledon development following germination.