Effect of Silicon on Activity of Antioxidant Enzymes and Photosynthesis in Leaves of Cucumber Plants (Cucumis sativus L.)

Abstract

The effects of exogenous silicon (Si) on changes of photosynthesis and the activities of major antioxidant enzymes such as guaiacol peroxidase (GPOD), siringaldasine peroxidase (SPOD) and antiradical activity (DPPH) as well as the content of polyphenols and photosynthetic pigments were investigated in leaves of young cucumber plants (Cucumis sativus L.), cv. Gergana. Plants were grown as a water culture in climatic boxes, under a PPFD of 350 µmol m-2 s-1. Five treatments consisting of a control (basic Hoagland nutrient solution without Si) and basic nutrient solution with 0.5 mM Si, 1.0 mM Si, 1.5 mM Si and 2.0 mM Si, were investigated. Plants were grown 15 days and analyses were performed at the end of experiment on the third leaf, which was fully developed. It was established that Si treatment increased photosynthetic activity of leaves. The variant with 1.5 mM Si has shown the highest photosynthetic rate. Activity of main antioxidant enzymes decreased in plant leaves and roots. The content of polyphenols was changed insignificantly in roots and in leaves of Si-treated plants. The content of pigments increased and highest values were established in variant with 1.5 mM Si. These results suggested that exogenous Si application in nutrient solution was useful to increase young cucumber antioxidant capacity and photosynthesis