SEASONAL, DEVELOPMENTAL AND VARIETAL EFFECTS ON PHOTOSYNTHETIC ENZYME-ACTIVITIES OF PEACH LEAVES (PRUNUS-PERSICA (L) BATSCH)

Chlorophyll, soluble protein content and the activities of RuBPC and PEPC were determined at different times during the growth season in leaves from six year old peach trees cv. Maycrest. PEPC activity did not change during the season, whereas protein content and RuBPC activity decreased significantly between May and July. RuBPC and glycolate oxidase activities changed with leaf age, showing the highest rates in fully expanded leaves. Maximum PEPC and MDH activities occurred in apical expanding leaves. The ratio of RuBPC to PEPC activity increased with leaf age, suggesting a possible role of PEPC in CO2 fixation in younger peach leaves. Small differences in RuBPC activity were observed in respect to other cvs (Springcrest, Fayette and Redhaven). RuBPC activity and the ratio of RuBPC to PEPC activity in peach leaves were always lower than those measured in apple and kiwifruit leaves. As in vivo photosynthetic rates of peach are similar to those of other horticultural woody species, it is suggested that the low activity of RuBPC might be due to inhibitory compounds in extracts of peach leaves.