SHORT-CHAIN SATURATED FATTY-ACIDS IN THE REGULATION OF POLLINATION-INDUCED ETHYLENE SENSITIVITY OF PHALAENOPSIS FLOWERS

Pollination greatly accelerates petal senescence. The first observed e vent after pollination is an increase in the flower's sensitivity to e thylene, followed by an increase in ethylene biosynthesis. Our objecti ves were to study the mode of action of the increase in ethylene sensi tivity and the possible involvement of short-chain saturated fatty aci ds (SCSFAs) in this process. Application of SCSFAs, ranging in chain l ength from 7 to 10 carbons onto stigmas of Phalaenopsis (Phalaenopsis hybrid, cv. Herbert Hager) flowers increased their sensitivity to ethy lene in the same way as pollination. Following pollination, there was a significant increase in the endogenous content of these fatty acids in the flower's column and perianth, with octanoic acid (C-8) being th e main SCSFA observed. The increase in SCSFA content was observed as e arly as 6 h after pollination and began to decline 6 h later. Incorpor ation of octanoic acid into liposomes or microsomal membranes isolated from Phalaenopsis petals resulted in a decrease in lipid order that w as detected by fluorescence polarization of dansyl pyrrolidine (DNSP) bur not of 1,6-diphenyl-1,3,5-hexatriene (DPH). At peak ethylene sensi tivity, 10 h after pollination, there was a significant decrease in th e lipid order of microsomal membranes isolated from Phalaenopsis colum ns and perianths, again as detected by DNSP but not by DPH. Stigmatic application of octanoic acid mimicked the effect of pollination on mem brane lipid order. We suggest that SCSFAs may be the ethylene 'sensiti vity factors' produced following pollination, and that their mode of a ction involves a decrease in the order of specific regions in the memb rane lipid bilayer, consequently altering ethylene action.