DOES GIBBERELLIC-ACID INHIBIT 2,4-DICHLOROPHENOXYACETIC ACID-INDUCED ETHYLENE PRODUCTION IN CUCURBITA-PEPO L SEEDLINGS

The development of the swelling of the hypocotyl base induced in C. pepo by 2,4-D was closely correlated with a marked increase in endogenous ethylene production and, although 2,4-D treatment was continuous for periods up to 8d, hypocotyl swelling was complete and 2,4-D-stimulated ethylene production had ceased within 5d and 3d respectively. The cobaltous ion, an inhibitor of ethylene biosynthesis, supplied in conjunction with 2,4-D, inhibited both hypocotyl swelling and ethylene production, but GA3, although suppressing 2,4-D-induced hypocotyl swelling, had no inhibitory effect on the levels of ethylene produced. It is concluded that increased ethylene levels, produced in response to 2,4-D treatment, are responsible for the abnormal growth patterns in hypocotyls of C. pepo, but although GA prevents this response to ethylene, it does not do so by suppressing ethylene production.