Studies on Elongation of Rice Coleoptiles

Abstract

It has long been recognized that the oxygen is not essential for the growth of coleoptile in rice plants. The reason, however, why the coleoptiles of rice plants are capable of growing and of performing its functions even under anaerobic conditions is not definitely understood. Several experiments were carried out in order to investigate the mechanism of rice coleoptiles in anaerobic conditions. The rice coleoptile elongates more rapidly and more extensively under anaerobic condition than in aerobic conditions. The elongation of coleoptile can not be inhibited by 2, 4-dichloro-anisole, that is an antiauxin. Rice coleoptile is a very exceptional tissue, and investigation of its elongation and respiration has led to some unusual results. Its very rapid elongation and respiration can not be inhibited by cyanide, azide, carbon monoxide, or malonic acid, that is to say, by any of the inhibitors to which cytochrome oxidase and its associated succinic acid dehydrogenase are particularly susceptible. No cytochrome oxidase can be extracted by the usual metods, and the other metallic-enzymes, polyphenol and ascorbic acid oxidase, seem to be absent also. Since the activity of homogenates is greatly increased by the addition of riboflavin, and the respiration of the tissue is markedly sluggish toward oxygen, it is probable that the role of the terminal oxidase might be here filled by a non-metallic flavoprotein enzyme.