Opposing Effects of Gibberellin and Ethylene

Whereas gibberellin and ethylene may both hasten abscission development in explant tissues (6, 7), and may provoke simi,lar actions in releasing some dormant buds or seeds (11, 17) in several growth functions these 2 regulators may have opposing types of effects. For example, ethylene and gibberellin (GA) ihave opposite effects in senescence development (3, 13). The reports that gibberellin can suppress fruit ripening (9, 10) suggest again an opposite effect from that of ethylene. In comparisons of several types of regulatory functions we have found ethylene and gibberellin effects to be opposite in sign. The possibility that ethylene and GA might have opposite types of effects was first examined with the lettuce hypocotyl bioassay for GA. Effects on lettulce hypocotyl elongation were measured according to Frankland and Wareing (14). Lettuce seedlings, germinated on filter paper for 48 hours, were placed on wet paper disks in 50 ml Ehrlenmeyer flasks stoppered with vaccine caps. Ethylene at 10 ppm was injected iby syringe into the flasks. After 72 ihours of growth in the light, the lengths of the seedling hypocotyls were meastured. The results, presented in table I, show that at GA concentrations between 0.1 and 10 mg/l, the presence of ethylene reduced the growth stimtulation. As a simpler system for comparing effects of ethylene and GA, we have used the hormonal induction of enzyme synthesis by GA. The induction of invertase formation in sugar beet tissue is known to be enhanced by GA (12). Invertase activitv in slices of sugar beet tissue (Beta vulgyiris L.) was measured according to Cherry (8) as modified from Bacon et al. (2). From mature stugar beets, cylinders of tissue were cuit with a No. 5 cork borer and sliced into 1 mm thick disks. Fiftv disks of tissue were placed in 125 ml Ehrlennieyer flasks with 20 ml of variouis concentrations of gibberellic acid. The flasks were stoppered with vaccine caps,