Temperature-dependent Inhibition of Hypocotyl Elongation in Some Soybean Cultivars: I. Localization of Ethylene Evolution and Role of Cotyledons 1 Downloaded from
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 "longhypocotyl" 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. Key words: Cotyledons -Ethylene -Hypocotyl elongation -Temperature sensitivity. Certain soybean cultivars exhibit poor emergence when planted at a depth of 10 cm and grown at 25°C. The poor emergence is a consequence of reduced hypocotyl elongation (Burris and Fehr 1971 Abbreviations: H, apical 2-cm hypocotyl segment; HW, wounded hypocotyl segment; C + E, cotyledons+ epicotyl; C + E+H, cotyledons+epicotyl + hypocotyl segment left attached to each other; pt, plant part; PVC, polyvinyl chloride; SD, standard deviation