Influence of calcium deficiency on superoxide generating-NADPH oxidase and antioxidant defense systems in bean root cells

Official URL: http://risc01.sabanciuniv.edu/record=b1081776 (Table of Contents)

Calcium (Ca) is an essential mineral nutrient element involved in growth and development processes of plants. There are several physiological processes, which are greatly affected by Ca nutritional status of plants such as cell extension, cell wall stabilization, signal transduction and membrane transport. Based on the studies in mammalian systems Ca was found to be effective on activity of superoxide radical (O2·̄) generating NADPH oxidases and antioxidative defense systems. The effects of Ca nutritional status of plants on NADPH oxidase and antioxidative defense systems in plant cells are rarely studied. In the present MSc study, the role of Ca on O2·̄ generating NADPH oxidase and antioxidative defense systems (i.e., superoxide dismutase, ascorbate peroxidase, glutathione reductase, catalase, ascorbic acid and non-protein sulfhydryl-compounds) was studied in cytosolic fractions of root cells by using bean (Phaseolus vulgaris, cv. Nassua) plants grown in nutrient solution with different Ca supplies (50 mM to 2000 mM). The results obtained show that exposure of Ca-adequate plants (2000 mM Ca supply) to different levels of deficient Ca supply (50 mM to 250 mM Ca) reduced the dry matter production and elongation of roots and caused brownish color formation along the roots. The decrease in root growth caused by Ca deficiency was more severe than the decrease in shoot growth. Compared to Ca-sufficient plants, the levels of NADPH oxidase and NADPH-dependent O2 generation were distinctly decreased in Cadeficient plants. This decrease was more pronounced at the lowest Ca supply (50 mM). Resupply of Ca to Ca-deficient roots for 8, 24 and 48 h markedly enhanced the activity of NADPH oxidase and the NADPH-dependent O2 generation. Pretreatment with the inhibitor of NADPH oxidase, diphenylene iodonium (DPI), inhibited the rate of NADPH-dependent O2·̄- generation by around 50 %. Analysis of antioxidant defense systems showed that Ca deficiency did not effect the ascorbic acid concentration, but markedly reduced the concentration of non-protein sulfhydryl (SH)-compounds (predominantly glutathione). Of the antioxidant enzymes, the superoxide dismutase, ascorbate peroxidase and catalase were not affected by Ca deficiency stress in roots. However, the activity of glutathione reductase was severely diminished by Ca deficiency, indicating a particular affect of Ca on redox status of glutathione in roots. The results indicate that Ca is required for generation of O2·̄ - by activating NADPH oxidase in root cells. As NADPH-dependent O2.- generation is involved in adaptive response of plants to different biotic and abiotic stress factors, maintenance of high activity of NADPH oxidase by adequate Ca supply was considered as a fundamental role of Ca in growth and development processes of plants.