Effect Of Ce(III) On Water Metabolism In Soybean Seedlings Under UV-B Radiation

Effect of Ce(III) on water content (RWC), water use efficiency(WUE) and stomatal behaviour in leaves of soybean seedlings exposed to two dosages of ultraviolet-B radiation (0.15, 0.45W·m-2) was studied detaily with hydroponics under laboratory conditions.The aim was to reveal protective effect of Ce(Ш) on water metabolism in soybean seedlings under UV-B radiation which would provide experimental gist for rare earths applied in agriculture. The main results were as follows:1. Static experimental results showed that 20mg·L-1 CeCl3 increased free water content in soybean leaves. For Ce(Ш)+UV-B treatments, the ratio of free water content and irreducible water content was higher than that of UV-B treatments. Dynamic results showed that Ce(Ш) eased UV-B radiation stress on water content in soybean leaves, accelerated the recovery pace. UV-B radiation affected two osmolytes (proline, soluble sugar) in soybean leaves oppositively which promated accumulation of free proline, but caused soluble sugar content dropping sharply. Ce(Ш) demonstrated an tagonistic effect on UV-B radiation which weakened free accumulation of proline, while increased the content of soluble sugar. Correlation analysis showed that Ce(Ш) improved the role of free proline and soluble sugar in regulating water content in soybean leaves under UV-B radiation.2. Static experiment results showed that 20mg·L-1 CeCl3 reduced decreasement of root activity, root length and root/shoot ratio induced by UV-B radiation. UV-B radiation caused the decline of Photosynthesis rate(Pn), Transpiration rate(Tr), while for Ce(III)+UV-B treatment the decline was eased. Water use efficiency (WUE) of soybean seedlings increased under low dosage of UV-B radiation(0.15W·m-2) stress(1st to 4th), then decreased sharply during the recovery periods(7th to 9th). Compared to CK, high dosage of UV-B radiation(0.45W·m-2) made WUE decreasing obviously. For Ce(Ш)+UV-B treatment, the decline rate of WUE was less than that of UV-B treatment, and WUE increased more rapidly during the recovery periods (7th to 9th).3. Static experiment showed that 20mg·L-1 CeCl3 improved stomatal density and high dosage of UV-B radiation(T2 0.45W·m-2) caused its'decline obviously compared to CK. For Ce(Ш)+UV-B treatments, the decline of stomatal density was lower than the corresponding UV-B treatments. UV-B radiation caused the decreasing of stamotal conductance(Gs), while under Ce(Ш)+UV-B treatments the Gs was larger than UV-B radiation, but smaller than CK. Diferent changes happened between ABA,H2O2,CAT and Gs. UV-B radiation caused accumulations of ABA, H2O2 and improvement of CAT's activity. Ce(Ш) reduced contents of ABA and H2O2 induced by UV-B radiation stress in leaves of soybean seedlings, improved CAT's activity.The experiment showed that Ce(III) played an effective role in defensing damage induc- ed by UV-B radiation stress on water metabolism of soybean seedlings.