Relationship between water content and afterripening in red rice

Abstract

Reactions regulating seed dormancy can proceed at water contents which are probably too low to permit metabolic activity. The loss of dormancy via afterripening of red rice. (Oryza sativa L.) seeds was examined as a representative case. Equilibration of seeds to various moisture contents showed that afterripening was most rapid at 6–14% moisture content (dry weight basis). Afterripening did not occur at > 18% moisture content and was severely inhibited at < 5% moisture content. Seed viability was greater than 95% for all treatments. Utilization of moisture isotherms to calculate water‐binding enthalpy values identified the optimal afterripening range as approximately the boundary between water‐binding region 1 and region 2. From these findings, it is suggested that afterripening may involve some oxidative reactions which are inhibited at lower water contents by the rising free‐energy and at the higher side by metabolic reactions.