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

Abstract

Researclh inito the physiological effects of gibberellic 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 22, 1959. increases, however, as germination progresses, and it is enhanced by compounds which stimulate germination. In addition, maltose is a compound commonly found in germinating grain and, with the exception of D-enzyme, the amylases are the only enzymes in higher plants known to be capable of its formation. It is difficult to conceive of starch hydrolysis in the endosperm taking place in the absence of amylase activity, and any indication of the release of sugar coincident with, and possibly even dlependent upon amylase activation would be useful in estimating the endogenous role of this enzyme. MATERIALS AND METHODSAll water used in these experiments was doubly glass distilled, and all GA solutions were freshly prepared the day of the experiment.RESPIRATION. Hordeurn distichumii var. Baku (a naked seed) and Prior (a husked seed) from the 1956 harvest were used. The husk of the Prior seeds was removed by hand and seeds of both varieties were cut in half transversely before treatment was commenced. The endosperm halves were incubated in the dark at 250 C for 18 hours. Petri dishes (4 in) containing eight endosperm halves and two sheets of filter paper, moistened with either 8 ml water or 8 ml water plus 200 gammas GA, were used. Following incubation, each sample of endosperm was rinsed thoroughly with water, blotted and weighed. The samples were then placed in Warburg flasks containing solutions similar to those of the initial soaking period (i.e., either 2 ml water or 2 ml water plus 200 gammas GA). The center wells contained 0.2 ml 10 % NaOH and the temperature was maintained at 250 C. STORAGE CONDITIONS. As noted by Merry and Goddard (10), seeds with a constant initial moisture content evidence much less variability than seeds with differing moisture contents. Consequently, Merry and Goddard's storage technique was adopted for all seeds other than those used in the respiration experi-

Physiological effects of gibberellic acid. III. Observations on its mode of action on barley endosperm

“…Gibberellic acid (GA3) is capable (in the excised endosperm in the complete absence of the embryo) of activating starch hydrolyzing enzymes, including a-amylase (9), and releasing reducing sugars (i.e. mobilizing the starch reserves) (8). On the basis of these results it was tentatively suggested (9) that a gibberellin-like hormone may act in vivo in a similar manner, being produced in the embryo and secreted into the endosperm where the hormone would bring about effects similar to those described.…”

Amylase activity in dormant and germinating seeds of Polygonum pensylvanicum

“…They were very similar in this respect to aleurone layers from oats described by Naylor (1966). Paleg (1960a and many subsequent workers have elucidated the role of gibberellin in the stimulation of amylase synthesis by aleurone layers of cereal prains.…”

Interactions between Ethylene, CO2, and ABA on GA3-Induced Amylase Synthesis in Barley Aleurone Tissue

“…Based on studies with barley and wheat aleurone tissue, this process is considered to be largely the result of gibberellininduced hydrolase synthesis (16,20). The hydrolase most frequently studied is a-amylase, and its synthesis is known to be additionally regulated by ethylene and ABA.…”