engleski

The role of photosinthesis and antioxidative enzymes in regulation of hydrogen peroxide level in senescing Maple leaves

Natural senescence of maple (Acer pseudoplatanus L.) leaves was investigated. Three types of senescing leaves were used in this study: green (G), yellow-green (YG) and yellow (Y) ones, respectively. Dramatic changes in hydrogen peroxide level were observed during senescence. H2O2 level in YG leaves decreased for 60% while in Y leaves increased about 140% in comparison to G leaves. The accumulation of starch without its degradation during the night was noticed in G and YG leaves, what served as probable signal to down regulate photosynthesis. It was achieved due to degradation of chlorophylls, decerese in photosystem II efficiency and decrease in photosinthetic oxigen production. Total carotenoids content decreased in YG (56%) and Y (58%) leaves with resect to green ones. Although that carotenoids level was lowered, it was high enough to assure efficient nonphotochemical qenching (NPQ). The studied antioxidative enzymes revealed different dynamics of their activities as well as their isoenzyme patterns. Activities of catalase (CAT), guaiacol-peroxidase (GPOD) and glutatihione reductase (GR) wre decreased in YG and Y leaves in comparison to G leaves, while activities of superoxide-dismutase (SOD) and ascorbate-peroxidase (APX) were remarkably up regulated during senescence. SOD activity was increased for about 400% in Y leaves in respect to G leaves, while its activity in YG leaves was not significantly different compared to G leaves. Accordingly, H2O2 level increased in Y leaves. Also, new isoenzymes of SOD, GPOD and CAT 3were detected in Y leaves.

photosynthesis; senescence; antioxidative enzymes; hydrogen peroxide; Acer pseudoplatanus

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