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Articles

Anomalous Temperature Dependence of Seedling Development in Some Soybean (Glycine max [L.] Merr.) Cultivars

Role of Ethylene ^1,2

^a Department of Botany and Plant Pathology, Iowa State University, Ames, Iowa 50011

In Clark and Shelby soybean (Glycine max [L.] Merr.) seedlings, hypocotyl elongation was inhibited and hypocotyl swelling and root dry weight were increased by a temperature of 25 C. At 20 and 30 C, development was normal, as was development of Hawkeye and Mandarin soybean seedlings at all three temperatures. Dry matter distribution at 9 days indicates that inhibition of hypocotyl elongation is not due to a lack of translocation from cotyledons, but to a diversion of dry matter from hypocotyl to root. Ethylene evolution by Clark seedlings at 25 C exceeds that at 20 and 30 C. At all three temperatures, Mandarin seedlings' ethylene evolution is at the same low rates as those of Clark at 20 and 30 C. Clark's enhanced rate at 25 C precedes the deceleration of hypocotyl elongation occurring at 5 days. The abnormal effects of a temperature of 25 C on Clark seedlings' development is partially reversed by CO₂ and GA₃ and can be duplicated in Mandarin by applying ethylene. In Clark, effects of the temperature can be further accentuated by indoleacetic acid, which stimulates ethylene evolution, and by applying ethylene to the seedlings. It is concluded that the temperature-induced symptoms, similar in most respects to the well known "triple response" of legume seedlings, are caused by abnormally high levels of ethylene in tissues of the anomalous cultivars.

¹ This work was supported in part by Cooperative Agreement No. 12-14-100-9364 (34), with Crop Research Division, Agricultural Research Service, United States Department of Agriculture.

² The material presented here derives mainly from a dissertation submitted by the senior author to the Department of Botany and Plant Pathology of Iowa State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy.