DEVELOPMENTAL-CHANGES OF ENZYMES OF MALATE METABOLISM IN RELATION TO RESPIRATION, PHOTOSYNTHESIS AND NITRATE ASSIMILATION IN PEACH LEAVES

The developmental profile of the activities of some enzymes involved in malate metabolism, namely phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31), NAD+-linked (EC 1.1.1.37) and NADP+-linked (EC 1.1.1.82) malate dehydrogenase (MDH), NAD+-linked (EC 1.1.1.39) and NADP+-linked (EC 1.1.1.40) malic enzyme (ME), has been determined in leaves of peach [Prunus persica (L.) Batsch cv. Maycrest], a woody C3 species. In order to study the role of these enzymes, their activities were related to developmental changes of photosynthesis, respiration, and capacity for N assimilation. Activities of PEPC, NAD(P)+-MDH and NADP+-ME were high in young expanding leaves and decreased 2- to 3-fold in mature ones, suggesting that such enzymes play some role during the early stages of leaf expansion. In leaves of peach, such a role did not seem to be linked to C2 photosynthesis or nitrate assimilation, in that photosynthetic O2 evolution and activities of nitrate reductase (EC 1.6.6.1) and glutamine synthetase (EC 6.3.1.2) increased during leaf development. In contrast, leaf respiration strongly decreased with increasing leaf age. We suggest that in expanding leaves of this woody species the enzymes associated with malate metabolism have anaplerotic functions, and that PEPC may also contribute to the recapture of respiratory CO2.