Effects Of Co-treatment Of Enhanced UV-B Radiation And Salt Stress On The Physiological And Biochemical Characteristics In Different Cultivars Of Hulless Barley Seedlings

UV-B radiation and salt stress seriously affect the growth of plants. At present, the studies on the mechanism of the cross adaptation of plants to the UV-B radiation and salt stress are still little. In this paper, the effects of co-treatment of enhanced UV-B radiation and salt stress on the physiological and biochemical characteristics in two cultivars of hulless barley (Dulihuang and Kunlunl2) were investigated. The main results are shown as follows:1、Under UV-B radiation alone, both hulless barley seedlings of Dulihuang and Kunlunl2 were all injured and Kunlun12 was more tolerance. The pretreatment of 200 mM NaCI for 48 h was almost no damage to both hulless barley seedlings. The damage induced by UV-B radiation was alleviated after pretreated with 200 mM NaCI.2、The treatment with UV-B radiation alone had almost no effects on the contents of proline (a osmotic adjustment substance) in both hulless barley leaves. And the proline contents in both hulless leaves increased in salt stress alone or in the co-treatments of UV-B radiation and salt stress. Meanwhile the proline content in Kunlunl2 leaves was higher than that in Dulihuang leaves.3、The accumulation of H2O2 increased in both leaves of two hulless barley. The accumulated H2O2 in Dulihuang leaves was higher than that in Kunlun12 leaves. The co-treatment of UV-B and NaCI stress could decrease the H2O2 content induced by UV-B stress. Further studies showed that the activities of antioxidant enzymes (POD, CAT, APX, GR and GPX) and the antioxidant (GSH) content significantly decreased in both leaves of hulless barley under UV-B radiation. And they decreased more in Dulihuang leaves compared to Kunlun12 leaves. The activities of antioxidant enzymes in the co-treatment of UV-B and NaCl stress were higher than that in UV-B radiation alone. But the antioxidant contents had little change. These results indicated that the co-treatment of UV-B and NaCl stress could regulate the activities of antioxidant enzymes in the leaves of hulless barley to enhance their resistance in UV-B stress.4、The contents of photosynthetic pigments and the chlorophyll fluorescence parameters in both hulless barley leaves decreased under UV-B radiation alone. And they decreased markedly in Dulihuang leaves than that in Kunlun leaves. The co-treatment of UV-B and NaCl stress could increase these parameters compared to UV-B radiation alone, suggesting that the pretreatment of salt stress could alleviate the damage of photosynthesis induced by UV-B stress.5、Anthocyanin and flavonoids are UV absorbing compounds to defense the injury of UV-B radiation to plant. The contents of anthocyanin and flavonoid in the leaves both in hulless barley accumulated largely under UV-B stress. They were further increase in the co-treatment of UV-B and NaCl stress. And the contents of anthocyanin and flavonoid in the leaves of Kunlun 12 was more than that in Dulihuang.In conclusion, the pretreatment with salt stress could alleviate the damage induced by UV-B radiation stress to both hulless barley seedlings. The protection of it may due to the pretreatment of salt stress could promote the accumulation of osmotic substance, increase in the activity of antioxidant enzymes and the contents of photosynthetic pigments, as well as regulate the chlorophyll florescence parameters and increase in contents of UV-absorbing compounds. Kunlun12 is more resistant to UV-B than Dulihuang since Kunlun12 could accumulate more protective substances under UV-B radiation stress.