Partial reduction in activities of photorespiratory enzymes in C < inf > 3 < /inf > -C < inf > 4 < /inf > intermediates of Alternanthera and Parthenium

Abstract

The maximum catalytic activities of several photorespiratory and photosynthetic enzymes were determined in leaf extracts of three C3-C4 intermediates (Alternanthera ficoides, A. tenella and Parthenium hysterophorus) and were compared to those of C3 (A. sessiles, Pisum sativum) and C4 (A. pungens, Zea mays and Amaranthus hypochondriacus) species. The activity levels of key photorespiratory enzymes, glycolate oxidase, catalase, NADH-hydroxypyruvate reductase and glycerate kinase were less (28 to 35% reduced) in intermediates than those of typical C3 species. Similarly, the activities of photorespiratory aminotransferases in the C3-C4 intermediates were also partially reduced (23 to 37% reduction). The activities of phosphoenolpyruvate carboxylase (PEPC), pyruvate, orthophosphate dikinase and NAD-malic enzyme were higher (2 to 7 times) in leaf extracts of the intermediates than those of C3 species. But the ratios of PEPC/rubisco in the C3-C4 intermediates were more like C3 than C4 species. We draw attention to the partial reduction in enzyme activity of photorespiratory metabolism, which could be an important factor for restriction of photorespiration in the C3-C4 intermediate species, in addition to enzyme compartmentation and/or operation of a 'C4-like' cycle © 1993 Oxford University Press.