Growth, Physiological Attributes and Antioxidant Enzyme Activities in Soybean Seedlings Treated With or Without Silicon Under UV-B Radiation Stress

Silicon (Si) can increase plant defence systems against abiotic and biotic stress, but there is little information on UV-B radiation stress alleviation by Si for field crops. Using soybean (Glycine max (L.) Mell) seedlings, we determined how Si may mediate UV-B radiation stress by studying changes in biomass, physiological attributes and antioxidants' activities. The seedlings were raised with 0, 1.70 and 2.55 mm of Si in the growth chamber under ambient, ambient +2.7 kJ m-2 day and ambient +5.4 kJ m-2 day of UV-B radiation. As expected, plants suffered severe growth limitations under UV-B radiation, but Si alleviated these limitations through improvements in leaf area (LA) and root-to-shoot ratio (R/S). The UV-B radiation stress reduced the LA by 73.9-94.7%, total dry weight (TDW) by 11.8-36.6% and R/S by 9.2-30.2% but induced the activities of soluble protein by 18.4-21.0%, catalase (CAT) by 22.7-54.2%, superoxide dismutase (SOD) by 31.9-63.1%, and peroxidases (POD) by as much as 162.9-381.6%. Further confirmation of stress alleviations by Si was noted from reductions in these stress signals (antioxidant activities) under UV-B radiation: CAT decreased significantly by 78.3-79.4%, SOD by 5.3-7.2% and POD by 49.9-61.9% in silicon-treated UV-B stressed soybean.