THE EFFECT OF ETHYLENE AND OTHER REGULATORS ON COLEOPTILE GROWTH OF RICE UNDER ANOXIA

Caryopses of rice (Oryza sativa L. cultivar 'Mercury') were imbibed for 2 days in water or 10-mu-M solutions of indoleacetic acid (IAA), kinetin, gibberellic acid or abscisic acid in the presence of a gas stream of air or nitrogen. Fully-imbibed caryopses were placed on agar in vertically-maintained Petri dishes in chambers in the dark at 29-degrees-C. Subsequent growth of roots and coleoptiles in air or nitrogen, with the later addition of 10-mu-l.l-1 ethylene, was determined. Rice seedlings grown in total anoxia in a nitrogen stream did not develop roots, but could do so if air or 0.5% oxygen was introduced after 3 or 4 days of anoxia. Coeloptile elongation in nitrogen proceeded at a rate comparable to that in air over the 5-day experimental period. Treatment of seedlings in air, during imbibition or during subsequent growth, with indoleacetic acid, gibberellic acid or ethylene promoted coleoptile elongation. The growth of coleoptiles in nitrogen was not enhanced in the presence of these growth promoters, and was inhibited by treatment with abscisic acid or kinetin. The role of endogenous regulators in cellular elongation under anoxia is discussed.