Physiology and biochemistry of leaf bleaching in prematurely aging maple (Acer saccharinum L.) trees: I. Hydrogen peroxide level, antioxidative responses and photosynthetic pigments

Abstract

Essential signaling processes such as changes in calcium mobilization, protein phosphorylation and gene expression are known to be modulated by hydrogen peroxide (H2O2). A lot of silver maple trees in the city of Osijek (Croatia) were noticed to have bleached leaves by early summer as well as during the whole vegetation season. In this study we aimed to investigate the processes that regulate H2O2 levels in healthy (green) and prematurely aged (bleached) leaves. For that purpose, photosynthetic performance and antioxidative response of green and bleached silver maple leaves were studied. Bleached leaves had higher hydrogen peroxide level, a three-fold level of total soluble proteins as well as a lower level of ascorbic acid. Concentrations of chlorophyll a, chlorophyll b, total chlorophylls and total carotenoids as well as maximum quantum yield of photosystem II were lower in bleached leaves. This indicated their impaired photosynthetic performance. Further more, bleached leaves were characterized by lower specific activities of the main antioxidative enzymes, which influenced their reactive oxygen species scavenging capability. The higher level of H2O2 content in bleached leaves as the consequence of reduced antioxidative enzyme specific activities as well as ascorbic acid level could be the reason for the down-regulation of photosynthetic performance and premature aging of those leaves.