Influence of Cobalt on Soybean Hypocotyl Growth and Its Ethylene Evolution

Development of dark-grown "Clark" soybean (Glycine max [L.] Merr.) seedlings is abnormal at 25 C but normal at 20 and 30 C. At 25 C, hypocotyls swell and fail to elongate normally; lateral root formation and seedling ethylene evolution are enhanced.Co(2+) promoted hypocotyl elongation of etiolated "Clark" soybean seedlings by 28% when grown at 25 C. The same growth-promoting concentration reduced hypocotyl thickness and primary root elongation by 28 and 43%, respectively. Co(2+) inhibited ethylene production both of intact seedlings and of apical 1-centimeter hypocotyl segments with attached epicotyls and cotyledons by 65 and 60%, respectively. These results suggest that Co(2+) exerts its effects on the hypocotyl growth by inhibiting ethylene production, and also confirm our previous conclusion that abnormal ethylene production at 25 C is responsible for the inhibition of hypocotyl elongation and for its swelling.