Physiological Effects of Gibberellic Acid: I. On Carbohydrate Metabolism and Amylase Activity of Barley Endosperm

Abstract

Researclh inito the physiological effects of gibberel-lic acid (GA) and other gibberellins has been confined largely to descriptive accounts of stimulatory (3) and inhibitory (18) actions, while few studies have attempted to integrate the action of GA with the normal physiological processes of the plant. One of the most clearly recognized stimulatory actions of GA is its ability to break dormancy (3), or conversely , its germination-promoting effect. Hayashi (7) demonstratedI that treatment with gibberellins hastened the germination of barley and rice and, more recently , other wvorkers have reported similar successes also with barley (8,12,19). A hastening of germination , as (lescribed by Hayashi, almost necessarily involves the increased breakdown of carbohydrate reserves in the endosperm, and although this tissue is well classified with respect to its carbohydrate. amino acid, and protein constituents, little is known about how its metabolism is controlled enzymatically. A recurring suggestion in the literature is that enzymilatic activity of the endosperm is derived by secretion of enzymes into that tissue by the embryo. Kirsop and Pollack (8) have demonstrated that there is, in fact, a positive correlation between the presence of the embryo and the pl-amylase content of the endo-spermii. with amylolytic action falling off sharply fol-lowving removal of the embryo. In 1947, however. Engel (5) showed that most of the pl-amylase in the barley grain was in the endosperm, so it is unlikely that f&-amylase secretion by the embryo plays a decisive role in the carbohydrate metabolism of the endo-spermii. The results of Kirsop and Pollack, then, may be interpretedl by postulating the secretion of some substance other than pl-amylase into the endosperm by the embryo. It is noteworthy, with respect to the