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 i n 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) ma late 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 ord er to study the role of these enzymes, their activities were related t o developmental changes of photosynthesis, respiration, and capacity f or N assimilation. Activities of PEPC, NAD(P)+-MDH and NADP+-ME were h igh in young expanding leaves and decreased 2- to 3-fold in mature one s, 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 photosyn thetic O2 evolution and activities of nitrate reductase (EC 1.6.6.1) a nd glutamine synthetase (EC 6.3.1.2) increased during leaf development . In contrast, leaf respiration strongly decreased with increasing lea f age. We suggest that in expanding leaves of this woody species the e nzymes associated with malate metabolism have anaplerotic functions, a nd that PEPC may also contribute to the recapture of respiratory CO2.