Temperature-dependent Inhibition of Hypocotyl Elongation in Some Soybean Cultivars: I. Localization of Ethylene Evolution and Role of Cotyledons1

Apical 2-cm hypocotyl segments from seedlings of a “short-hypocotyl” cultivar Amsoy 71, like whole seedlings, evolve about twice as much ethylene at 25°C as at 30°C. Segments consisting of two cotyledons and an attached epicotyl evolve ethylene at low rates at both 25°C and 30°C. Hypocotyl segments from seedlings of Cutler 71 also show enhanced ethylene evolution at 25°C. Hypocotyl segments from Corsoy, a “long hypocotyl” cultivar, however, evolve ethylene at low rates at both 25°C and 30°C. Wounding of Amsoy 71 hypocotyl segments does not increase their ethylene evolution. Ethylene evolution at 25°C is reduced and the short-hypocotyl phenomenon is reversed by partial (50%) removal of Amsoy 71 cotyledons at planting time.