CHEMICAL MODIFICATION OF ETHYLENE RESPONSES IN PLANTS

The means of prevention of ethylene injury to plants or cut flowers has occupied these meetings but relatively little has been said about the inhibition of ethylene synthesis and some of the physiological phenomena caused by this gas. It appears that an understanding of the actions of chemicals used in the preservation of cut flowers may rationalize their usage and add to the understanding of the role of ethylene in plant life and to the prevention of its injurious effects. The aim of this paper is to present and discuss some of these topics.

The citrate and sulphate esters of 8-hydroxyquinoline (8-HQ) have found a wide application in the floricultural industry as components of preservative solutions (Marousky, 1972; Parups and Chan, 1973). Use of these salts has contributed to the extension of longevity of cut flowers, particularly roses, by eliminating or decreasing the blocking of xylem vessels, probably because of the bacterio- and fungi-static action of 8-HQ (Larsen and Cromarty, 1967). In an extension of these studies, Marousky, 1972 suggested that the blockage of rose xylem may not be principally to microbial occlusion but to other physiological changes in the stem and that 8-HQ might have another function as well as that of a bactericide. These unspecified effects of 8-HQ in delaying the climacteric in cut flowers have been observed previously (Larsen and Frolich, 1969).

The effect of 8-HQ on synthesis of ethylene was tested using a system containing slices of ripe apple., cv. 'McIntosh', or stamens of green-house-grown roses, cv. 'Forever Yours'.

Addition of 40–640 ppm of 8-HQ to the reaction mixture containing 5 g of apple slices decreased the ethylene production from 10.2 ppm in the control treatment to less than 0.5 ppm in the treatment containing 640 ppm of 8-HQ (Table1). Microbial contamination in these and other reaction mixtures was tested and showed that with increasing concentrations of 8-HQ in the test systems there were corresponding decreases in growth of micro-organisms but that even with the highest concentration, 640 ppm, such growth was not eliminated entirely. For example, the addition of 160 ppm of 8-HQ to the system, approaching the concentrations common in the floral preservative solutions, reduced the ethylene level to 26.6% of the control. At the highest level, 640 ppm of 8-HQ, the ethylene level was suppressed still, further to 4.2% of the control and, although the growth of micro-organisms was retarded, neither of these systems was sterile. This showed that the direct effect of 8-HQ on the