Structure requirements of corticosteroids for physiological activity in etiolated mung bean seedlings

Abstract

We studied the structure-activity requirements of corticosteroids in etiolated mung bean seedlings. 1. Glucocorticoids are very active in mung beans. Most of them double elongation growth of the root and double lateral root number. After a 72 hr growth period, they stimulate hypocotyl growth by ± 50%. In this group one finds: Cortisol, corticosterone, Δ 1 -cortisol, cortisone and Δ 1 -cortisone. 2 α -methyl-cortisol is an exception and inhibits growth. 2. 11-keto-corticosteroids (cortisone, Δ 1 -cortisone) are less active than their corresponding 11 β -OH-forms (cortisol, 11-cortisol), probably because the conversion of the 11-ketofunction into an 11 β -OH is very slow. 3. Precursors of corticosteroids with an 11 β -OH-group (11 β -OH-progesterone, 21-desoxy-cortisol) are very active; precursors lacking this 11 β -OH. (11-desoxy-cortisol, 11-desoxy-corticosterone) inhibit growth or are inactive. 4. 11-desoxy-corticosteroids (11-desoxy-cortisol, 11-desoxy-corticosterone) probably are not converted to their corresponding 11 β -OH-forms. These steroids have a mineralocorticoid activity (in animals), like aldosterone and 2 α -methyl, 9 α -fluoro-cortisol. These mineralo-corticoids inhibit growth or are inactive. 5. Reduced excretion products of glucocorticoids (in animals) are very active in mung bean seedlings, but not in animals. To this group belong: 5 β -dihydro-cortisol, tetrahydrocortisol (THF) and Reichstein's substance E. Results suggest that also in higher plants corticosteroids have a hormonal function and possibly have to be considered as a new group of plant steroid hormones .