THE O2 AND NO2- PHOTOREDUCTION IN CHLOROPLASTS OF SUN AND SHADE LEAVES OF WOODY PLANTS

Abstract:

O₂ and NO₂^- photoreduction in chloroplasts isolated from the leaves of Castanopsis fissa (tree) and Psychotria rubra (shrub) seedlings grown under three light intensities were compared in the presence of glyceraldehyde (an inhibitor of PCR and PCO cycle activity) and NH₄Cl (uncoupler of photophosphorylation). The highest rate of O₂ photoreduction (Mehler reaction) was observed in chloroplasts from full sun-exposed leaves of both plants,which was 66%-68% of total electron transport. NO₂^- photoreduction showed a similar trend， but it was only l1％-15％ of total electron transport activity．Shade leaves exposed to 36％ and 16％ of full sun light significantly decreased the photoreduction rates of 0₂ and NO₂^- and the percentage of 0₂ photoreduction to total electron transport，but had no effect on the percentage of electron transport partitioning to NO₂^- photoreduction． The activities of nitrite reductase(NiR)，nitrate reductase (NR)in leaves and the ratio of NiR／NR activity were also afFected by light intensity．As the light intensity was reduced，NiR activity decreased in C. fissa，and NR activity increased in P．rubra， whereas the changes in NR activity in C. fissa or NiR activity in P. rubra were not significant．The ratio of NiR/NR activity in two sun leaves reached more than 3，and it was just 1.7—2.2 in shade 1eaves．