GLYCOLATE ACCUMULATION CAUSES A DECREASE OF PHOTOSYNTHESIS BY INHIBITING RUBISCO ACTIVITY IN MAIZE

The consequences of interruption of the photorespiratory cycle by phos phinothricin (PPT) and aminooxyacetic acid (AOA) in several aspects of maize photosynthesis were investigated. Both compounds inhibited the photorespiratory pathway, causing glycolate accumulation and photosynt hesis inhibition. PEPCase activity was not affected by PPT or by AOA, but NADP-ME activity was slightly increased. The inhibition of RUBISCO activity was not due to depletion of its substrates, neither CO2 nor RuBP. An inverse relationship was found between glycolate accumulation and RUBISCO activity when photorespiration is blocked by PPT or AOA. We suggest that the accumulation of the photorespiratory metabolite, g lycolate, provokes the inhibition of RUBISCO activity, and consequentl y diminution of CO2 assimilation.