Effects Of Cerium On Photosynthetic Light Reactions In Plants Exposed To Supplementary Ultraviolet-B Radiation

Gradual depletion of stratospheric ozone layer in atmosphere has lead to increase in solar UV-B radiation that reaches earth surface. Many investigations concerning the influence of UV-B radiation on different terrestrial plants were carried out during the last 25 years. Study on the effect of rare earths elements on plants exposed UV-B radiation aimed to develop and extend the research for environmental botany of rare earths. The results of this study could provide a new direction for the ecological protection of plants against the damage of UV-B radiation. In this paper, effects of cerium(Ⅲ) on photosynthetic light reactions in soybean seedlings exposed to supplementary ultraviolet-B radiation(UV-B) were studied by hydroponics under laboratory conditions. Various techniques such as photosynthetic gas exchange, chlorophyll fluorescence as well as scanning electron microscope were used to investigate the regulating mechanism of Ce(Ⅲ) on photosynthetic primary reaction, electron transport, photosynthetic oxygen evolution and photophosphorylation and changes of chloroplast ultrastructure in leaves exposed UV-B radiation. The main results were below:i. Dose-effect and time-effect relation between the dose of Ce(Ⅲ) and photosynthetic rate in leaves of soybeanDynamic changes of photosynthetic rate(Pn) in leaves sprayed with Ce(Ⅲ) solution at various concentration showed that the trends with different treatments was not the same during 15 day, and proved that the effect of Ce(Ⅲ) on Pn were closely related to its concentration and treating time. The increase range of Pn in leaves treated with 20mg·L-1 Ce(Ⅲ) was largest and the period with higher lever was longest, which proved that this concentration was suitable in our experiments.ii. Dose-effect relation between the intensity of UV-B radiation and photosynthetic rate in leaves of soybeanChanges of Pn in leaves exposed different intensity of UV-B radiation showed that Pn was significantly and negatively correlated with intensity of UV-B radiation. Compared with the control sample, Pn was significantly decreased in leaves exposed to UV-B radiation at the level of 0.15W·m-2 while Pn was decrease more than 50% in leaves exposed to UV-B radiation at the level of 0.45W·m-2. In our experiment, the lower intensity of UV-B radiation was 0.15W·m-2 and the higher one was 0.45W·m-2.iii. The protective effect of Ce(Ⅲ) on photosynthesis in leaves of soybean against the damage of UV-B radiation...