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During development, the ribonuclease activity of maize endosperm homozygous for the opaque-2 gene increased earlier and, after a longer period of exponential increase, was much higher finally than in normal endosperm. The maximum difference was about sixfold and occurred 22 to 25 days after pollination. Heterozygotes on day 23 did not show a comparable increase in endosperm activity. No difference in the activity ratio (pH 6.0: pH 5.2) was found between normal and opaque-2 endosperm, indicating that the increase in activity in opaque-2 was due solely to an increase in ribonuclease A. The ribonuclease activity of opaque-2 embryos increased more rapidly than that of normal embryos, but the final activity was the same in each case.

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