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In situ synthesis and degradation of ribulose bisphosphate carboxylase (RuBPCase) were studied quantitatively in the 12th leaf blade of the rice plant during the life span of the leaf. Levels of RuBPCase protein were determined by rocket immunoelectrophoresis. The amounts of RuBPCase synthesized and degraded were estimated using ¹⁵N tracer.

RuBPCase was scarcely recognized in the leaf when the tip of the leaf had just emerged from the 1 lth leaf sheath. Then it increased rapidly and reached its maximum content a week after the completion of leaf expansion. At this time RuBPCase accounted for 56% of the soluble leaf protein N (26% of the total leaf N). The total amount of RuBPCase synthesized up to this time was about 90% of the amount synthesized throughout the leaf's life.

Degradation of RuBPCase started about the time when it reached the maximum content and proceeded at a faster …