Biochemical Changes in the Rice Grain during Germination

Abstract

Changes in the content of starch, protein, and RNA and in the activity of their hydrolases in the rice endosperm (Oryza sativa L., variety IR8) were determined during the first week of germination without added nutrient both in the dark and in the light. Changes were generally more rapid in the dark than in the light. Oxygen uptake and RNase activity started to increase and the root protruded on the second day, followed by the coleoptile on the third day, and the primary leaf on the fourth day. ATP level was at a maximum on the fourth day. The activity of amylases and R enzyme increased progressively, but that of phosphorylase tended to decrease during starch degradation. A new alpha amylase isozyme band appeared during germination. Glucose was the major product of starch degradation. Sucrose, maltose, maltotriose, raffinose, and fructose were also detected. Protease activity reached a maximum on the fifth or sixth day and closely paralleled the increase in soluble amino N and soluble protein.In embryoless seed halves with 0.12 muM gibberellin As, peak protease activity occurred in 2.5 days and peak alpha amylase activity on the fifth day of incubation. The production of alpha amylase, protease, and R enzyme was inhibited by 40 muM cycloheximide, but only alpha amylase and R enzyme were inhibited by 20 mug/ml actinomycin D.