EXAMINATION OF THE POSSIBLE INVOLVEMENT OF LIPOXYGENASE AND JASMONATES IN POLLINATION-INDUCED SENESCENCE OF PHALAENOPSIS AND DENDROBIUM ORCHID FLOWERS

Application of linoleic and linolenic acids to Phalaenopsis and Dendro bium flowers enhanced their senescence and promoted ethylene productio n. This effect was specific to unsaturated fatty acids which serve as substrates for lipoxygenase action, and did not occur following simila r treatments with saturated fatty acids. Several major lipoxygenase pa thway metabolites including jasmonic acid methyl eater, traumatic acid , trans-2-hexenal and cis-3-hexenol also enhanced flower senescence. J asmonic acid methyl ester promoted ethylene production by Phalaenopsis flowers. In contrast, treating flowers with the lipoxygenase inhibito rs salicylhydroxamic acid and n-propyl gallate, which inhibite(d) lipo xygenase activity in vitro, had no effect on pollination-induced senes cence of the flowers. Furthermore, during the 50-h period following po llination, there was no increase in lipoxygenase activity in Phalaenop sis flowers. During the 10-h period from pollination of Dendrobium flo wers until the initiation of ethylene production, there was no effect of pollination on jasmonate levels in either the perianth or the colum ns. These results suggest that lipoxygenase activity and jasmonates ar e not directly involved in pollination-induced Phalaenopsis and Dendro bium flower senescence.