Changes in photosynthesis, antioxidant enzymes and lipid peroxidation in soybean seedlings exposed to UV-B radiation and/or Cd

Aims The objective of this research was to study the effects of ultraviolet-B (UV-B) radiation and cadmium (Cd), applied individually, in combination, and alternately in soybean (Glycine max L) seedlings. Methods Pigment content, photosynthetic parameters, chlorophyll fluorescence and antioxidant enzymes (i.e., catalase (CAT), superoxide dismutase (SOD), guaiacol peroxidase (POD)), and malondialdehyde (MDA) content were investigated. Observations began 6 days after the exposure to Cd (40 mgkg(-1)), UV (7.1 kJ m(-2)) and Cd+UV, as well as 3 days after the exposure to Cd/(or) UV followed by exposure to Cd+UV (i.e., Cd similar to Cd+UV, UV similar to Cd+UV). Results After 6 days of treatment, all treatments showed lower shoot dry weight relative to controls, except Cd similar to Cd+UV. Cd and Cd+UV significantly (P < 0.05) decreased root length and root dry weight. UV-B and Cd alone significantly (P < 0.05) reduced pigment content, net photosynthetic rate, stomatal conduction, transpiration and SOD activity, and significantly (P < 0.05) increased MDA content. Cd also significantly (P < 0.05) reduced chlorophyll fluorescence but increased H2O2 contents. Compared to individual treatments, the combined effect was more detrimental to the above parameters. The sequential treatments (Cd similar to Cd+UV or UV similar to Cd+UV) were no or less detrimental compared to the combined treatments. Conclusions This is the first report of the sequentially applying UV-B and Cd stress. Reduced detrimental effects by the sequential application compared to the combination suggested the cross-adaptation of Cd and UV-B mediated protection of Cd+UV in soybean.