Changes in Antioxidant Defense Capacity in Crop Plants Depend on Leaf Developmental Periods

Abstract

In this study, chlorophyll, antioxidant compounds and antioxidant enzyme activities of five crop plants (Lycopersicum esculentum Miller, Solanum melanogena L., Capsicum annuum L., Lactuca sativa L. and Cucumis sativus L.) were analyzed in leaves at different development phases (sink, source and senescent). Leaf dry weight decreased, while relative water content increased in all species except C. sativus, depending on leaf development level. Chlorophyll amount significantly decreased with senescence, while carotenoids were found to be well preserved during senescence. It was found that ascorbic acid and tocopherol contents and antioxidant enzyme activities decreased in senescent leaves when compared to young sink and mature source leaves. High GR activities of sink leaves decreased at source and senescent phases. GR activity was preserved in L. esculentum and C. sativus during the senescent phase. It was found that high SOD activity of sink leaves was significantly preserved in source and senescent laves. The findings indicate that young sink leaves need antioxidant protection and after the elimination of this need in the senescent phase, the antioxidant capacity of leaves decreased. We suggest that the relationship between antioxidant defense system and developmental phases show significant variations according to plant species

Keywords

• Antioxidant compounds, Antioxidant enzymes, Senescence, Sink leaf, Source leaf