Examination of the possible involvement of lipoxygenase and jasmonates in pollination‐induced senescence of Phalaenopsis and Dendrobium orchid flowers

Abstract

Application of linoleic and linolenic acids to Phalaenopsis and Dendrobium flowers enhanced their senescence and promoted ethylene production. This effect was specific to unsaturated fatty acids which serve as substrates for lipoxygenase action, and did not occur following similar treatments with saturated fatty acids. Several major lipoxygenase pathway metabolites including jasmonic acid methyl ester, traumatic acid, trans‐2‐hexenal and cis‐3‐hexenol also enhanced flower senescence. Jasmonic acid methyl ester promoted ethylene production by Phalaenopsis flowers. In contrast, treating flowers with the lipoxygenase inhibitors salicylhydroxamic acid and n‐propyl gallate. which inhibite(d) lipoxygenase activity in vitro, had no effect on pollination‐induced senescence of the flowers. Furthermore, during the 50‐h period following pollination, there was no increase in lipoxygenase activity in Phalaenopsis flowers. During the 10‐h period from pollination of Dendrobium flowers until the initiation of ethylene production, there was no effect of pollination on jasmonate levels in either the perianth or the columns. These results suggest that lipoxygenase activity and jasmonates are not directly involved in pollination‐induced Phalaenopsis and Dendrobium flower senescence.