SHIFTS IN PHOTOSYNTHETIC CARBON LABELLING PATTERN BY ETIOLATED RICE (ORYZA SATIVA L.) SEEDLINGS DURING GREENING

Abstract

The carbon assimilation pattern in light by dark‐grown rice Oryza sativa seedlings was studied during greening. After exposure of etiolated seedlings to light their capacity to synthesize the C4‐acids, malate and aspartate, increased for 12 h. The labelling of 3‐phospho‐glycerate, sugar phosphates, sucrose and insolubles, did not increase until after 12 h. Thereafter a continuous steep increase in synthesis of Calvin cycle intermediates, but not of C4‐acids, recurred. The levels of carboxylating enzymes (phosphoenolpyruvate and ribulose diphosphate carboxylases) in the seedlings correlated positively with the appearance of label in C4 acids and in Calvin cycle compounds. We suggest that a β‐carboxylation mechanism was activated immediately on illumination but was persistent for only 12 h. After an 8‐h lag period following illumination, the Calvin cycle began to operate and continued during further growth of seedlings in light. Copyright © 1977, Wiley Blackwell. All rights reserved