Physiological Effects On UV-B Resistance Of Wheat(Triticum Aestivum L.) Seedlings Mediated By Exogenous Jasmonic Acid

The depletion of O3has been resulting the enhancement of UV-B radiation reaching the ground. UV-B radiation has an important biological effect on the plant. Increased radiation certainly will cause serious influence on plants needing light for energy, which are sensitive to enhanced UV-B radiation. And in the long-term of evolutive process, higher plants develop a complicatedly and subtly adaptative mechanism which could response the change of external and internal environment, adjust the growth and differentiation, maintain the proper living condition to adapt and resist harmful environmental stress, including plant hormones played a key role. At present, the new type plant hormones-jasmonic acid (JA) has been concerned for its widely physiological effect.In order to understand the protected effects of jasmonic acid (JA) on wheat exposed to ultraviolet B (UV-B) radiation stress. The20-day-old wheat(Triticum aestivum L., cv. Xinong88) seeding was pretreated with different concentration of JA (1,2.5,5,7.5and10mmol/L) before adding UV-B radiation. Then the physiology characteristic (such as pigment content, protective enzyme activities, lipid peroxidation level, UV-B absorbance compounds content and so on) and the growth parameters among the control and JA treatment groups were analyzed. With the research object of exogenous JA, this study investigated whether exogenous JA could alleviate UV-B stress or not, and tryed to explore the physiological effect of exogenous JA improving wheat seedlings UV-B resistance, thus contributed to realize and speculate the interactive network of UV-B radiation and exogenous JA.The main conclusions are listed as follows:1. Exogenous JA could eliminate the negative influence of UV-B radiation stress to improve UV-B resistance of wheat seedlings. Exogenous JA-induced strategies of UV-B tolerance in wheat seedlings mainly included enhancement activity of some antioxidative enzymes, accumulation of free proline and anthocyanin content and promotion of the proportion of open PSII centers to repair damage of membrane lipid peroxidation to some extent.2. Exogenous JA has the effect of concentration on plants stressed by UV-B radiation. Exogenous1mmol/L JA could weaken the influence of antioxidant defense system suffering from7d UV-B radiation through improving SOD, CAT and POD activity and UV-absorbing compounds to strengthen the UV-B radiation resistance of plant. Under7d UV-B radiation, exogenously applied2.5mmol/L JA would improve total leaf chlorophyll, free proline and anthocyanins content of wheat seedlings, and enhance the root activity. Moreover, exogenous1and2.5mmol/L JA both could reduce lipid peroxidation level. Therefore, make sure the appropriate concentration of improving UV-B resistance.3. There was an interactive effect between UV-B radiation and exogenous JA. When plant exposure to UV-B radiation for12h, antioxidant system, MDA, the free proline, Fo, Fm,ΦPSII, Fv’/Fm’,qP, ETR and NPQ were significantly affected by UV-B radiation. And antioxidant system, MDA, UV-absorbing compounds, anthocyanin, photosynthetic pigments, Pmax, LCP and chlorophyll fluorescence parameters were affected by exogenous JA. While antioxidant system, MDA, the free proline, anthocyanin, Fm, Fv/Fm,ΦPSII, Fv’/Fm’, ETR and NPQ were disturbed strongly by the interaction of UV-B radiation and exogenous JA. Additionally, from the statistical analysis of related physiological effects, we found out the role of exogenous JA responding to UV-B radiation is antagonistic effect.4. Accompanying with the wavy effect of18-h UV-B radiation on physiological parameter, the influence of exogenous JA on these parameters of UV-B stressed wheat was also fluctuant. The physiological response of UV-B stressed wheat to exogenous JA presented time dependence significantly. In addition, there was time-effect of exogenous JA and the interaction of UV-B radiation and exogenous JA on wheat seedlings. In the later stage of this trial, the interaction of UV-B radiation and exogenous JA was mild attenuation with the time increasing. However, during3-12h UV-B radiation phases, the interactive effect presented increasing trend.In short, there was the time and concentration dependence of exogenous jasmonic acid (JA) on enhanced UV-B oxidative stress resistance of wheat seedlings. Jasmonic acid, especially at the lower concentration (1and2.5mmol/L), was involved in the mechanism of UV-B oxidative stress tolerance by enhancing activity of some antioxidative enzymes, accumulating free proline and anthocyanin content, promoting of the proportion of open PSII centers, repairing damage of membrane lipid peroxidation to some extent, which contributed to reduce membrane damage caused by UV-B stress. In addition, identify there was an interactive effect between UV-B radiation and exogenous JA through the statistical analysis. And this interaction was the antagonistic effect.