Effect of cerium on photosynthetic pigments and photochemical reaction activity in soybean seedling under ultraviolet-B radiation stress.

Effects of cerium (Ce) on photosynthetic pigments and photochemical reaction activity in soybean (Glycine max L.) under ultraviolet-B (UV-B) radiation stress were studied under laboratory conditions. UV-B radiation caused the decrease in chlorophyll content, net photosynthetic rate, Hill reaction activity, photophosphorylation rate and Mg(2+)-ATPase activity. Ce (III) (20 mg L(-1)) could alleviate UV-B-induced inhibition to these photosynthetic parameters because values of these photosynthetic parameters in Ce (III) + UV-B treatment were obviously higher than those with UV-B treatment alone. Dynamic changes of the above photosynthetic parameters show that Ce (III) could slow down the decrease rate of these photosynthetic parameters during a 5-day UV-B radiation and quicken the restoration during recovery period. The final restoration degree of five parameters mentioned above in leaves exposed to low level of UV-B radiation (0.15 W m(2)) was higher than that exposed to high level (0.45 W m(2)). Correlating net photosynthetic rate with other four parameters, we found that the regulating mechanisms Ce (ΠΙ) on photosynthesis under various level of UV-B radiation were not the same. The protective effects of Ce (III) on photosynthesis in plants were influenced by the intensity of UV-B radiation.