Amplification of abiotic stress tolerance potential in rice seedlings with a low dose of UV-B seed priming

UV-B radiation is a major abiotic stress factor that adversely affects the growth and productivity of crop plants including rice (Oryza sativa L.). However, on the other hand, lower doses of UV-B radiation applied to seeds can have a priming effect on plants emerging from it. In this study, seeds of O. sativa var. kanchana were primed with UV-B radiation (6 kJ m-2) and were further subjected to NaCl, polyethylene glycol 6000 (PEG) and UV-B stress. The effects of UV-B priming in imparting NaCl, PEG and UV-B stress tolerance to rice seedlings were analysed through various photosynthetic features and antioxidative mechanisms. PSI and PSII activity levels as well as chl a fluorescence were found to be significantly higher in the UV-B primed and unstressed seedlings. When stress (NaCl, PEG and high UV-B) was imposed, increased PSI and PSII activity levels, chl a fluorescence and metabolite accumulation (proline, total phenolics and sugar) as well as nonenzymatic (ascorbate and glutathione) and enzymatic (superoxide dismutase, catalase, ascorbate peroxidase) antioxidants were recorded in UV-B primed and NaCl-stressed plants followed by UV-B primed and UV-B-stressed plants, and primed and PEG-stressed, compared with unprimed and stressed conditions. The results indicate that UV-B priming in rice seedlings effectively enhances the NaCl stress tolerance potential in rice to a greater extent than UV-B and PEG stress tolerance potential. The cost-effectiveness of UV-B seed priming is predominantly clear from the differing tolerance responses of rice seedlings exposed to different stress conditions.