Free radical generation and antioxidant content in chloroplasts from soybean leaves exposed to ultraviolet‐B

Abstract

The aim of this work was to study the effect of ultraviolet‐B (UV‐B) exposure on oxidative status in chloroplasts isolated from soybean (Glycine max cv. Hood). Chloroplasts were isolated from soybean leaves excised from either control seedlings or those exposed to 30 and 60 kJ m−2 day−1 of UV‐B radiation for 4 days. Chloroplastic oxidative conditions were assessed as carbon‐centered radical, carbonyl groups and ascorbyl radical content. Treatment with UV‐B increased the carbon‐centered radical‐dependent EPR signal significantly by 55 and 100% in chloroplasts from leaves exposed to 30 and 60 kJ m−2 day−1 UV‐B, respectively, compared to radical content in chloroplasts from control leaves. The content of carbonyl groups increased by 37 and 62% in chloroplasts isolated from soybean leaves irradiated for 4 days with 30 and 60 kJ m−2 day−1 UV‐B, respectively. The content of soluble metabolites in isolated chloroplasts should not be taken as absolute in vivo values; however, these data are valuable for comparative studies. UV‐B exposure did not significantly affect ascorbyl radical content compared to controls. The content of ascorbic acid and thiols in chloroplasts isolated from leaves exposed to 60 kJ m−2 day−1 UV‐B was increased by 117 and 20.8%, respectively, compared to controls. Neither the content of total carotene nor that of β‐carotene or α‐tocopherol was affected by the irradiation. The results presented here suggest that the increased content of lipid radicals and oxidized proteins in the chloroplasts isolated from leaves exposed to UV‐B could be ascribed to both the lack of antioxidant response in the lipid soluble fraction and the modest increase in the soluble antioxidant content.