Influence of Cobalt on Soybean Hypocotyl Growth and Its Ethylene Evolution

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Abstract
Development of dark-grown Clark soybean (Glycine max [L.] Merr.) seedlings is abnormal at 25.degree. C but normal at 20 and 30.degree. C. At 25.degree. C, hypocotyls swell and fail to elongate normally; lateral root formation and seedling ethylene evolution are enhanced. Co2+ promoted hypocotyl elongation of etiolated Clark soybean seedlings by 28% when grown at 25.degree. C. The same growth-promoting concentration reduced hypocotyl thickness and primary root elongation by 28 and 43%, respectively. Co2+ inhibited ethylene production both of intact seedlings and of apical 1 cm hypocotyl segments with attached epicotyls and cotyledons by 65 and 60%, respectively. These results suggest that Co2+ exerts its effects on the hypocotyl growth by inhibiting ethylene production, and also confirm our previous conclusion that abnormal ethylene production at 25.degree. C is responsible for the inhibition of hypocotyl elongation and for its swelling.