Effect Of Exogenous Nitric Oxide On Physiological Characteristics Of Taxus Chinensis Var. Mairei Seedlings Under UV-B Stress

The principal ultraviolet radiation absorbance occurs in the stratospheric ozone layer in earth’s atmosphere. The destruction of this layer, which is caused by ozone depletion, has lead to an increase in solar UV-B radiation (280-320nm) reaching the Earth’s surface and produced potentially biological effect for plants in the earth. Nitric oxide (NO) as the second messenger of the UV-B radiation has been the most activity research hotspot in plant stress physiology and signal transduction fields.In this experiment,5-year-old Taxus chinensis var. mairei seedlings were used as experiment material to studied the effect on the concentrations of photosynthetic pigments, contents of free radicals, activities of antioxidant enzymes, concentrations of flavonoids and other physiological indicators of T. chinensis var. mairei seedlings under enhanced UV-B radiation, by spraying exogenous sodium nitroprusside(SNP), a donor for NO. We revealed the adapted mechanism of exogenous NO on physiological characteristics in T. chinensis var. mairei seedlings under enhanced UV-B radiation. The main results are as follows:Our results showed that the contents of hydrogen peroxide(H2O2), hydroxyl free radicals(-OH) and malondialdehyde(MDA) were significantly increased by enhanced UV-B radiations (P<0.05). The UV-B treatment induced the activities of peroxidase (POD) and superoxide dismutase(SOD) increased, but significantly decreased the activities of catalase (CAT) and ascorbate peroxide(APX)(P<0.05) and the contents of soluble protein. The contents of UV-B absorbing compounds (flavonoids, total phenols and tannin), carotenoid and taxol were significantly increased by enhanced UV-B radiations(P<0.05). Under UV-B stress, spraying exogenous0.1mM-L"1SNP significantly increased the net photosynthetic rate, photosynthetic pigments contents, antioxidant enzymes activities and secondary metabolism substance contents, reduced H2O2and MDA contents. Thus exogenous NO could maintain the balance of active oxygen metabolism, protect membrane structure of T. chinensis var. mairei seedlings. Thereby, T. chinensis var. mairei seedlings could resist UV-B stress damage.In a word, the results demonstrate that NO as a molecule of plant defense signal, is widely involved in response and defense of T. chinensis var. mairei seedlings under UV-B stress. NO as second message of UV-B radiation mediated UV-B stress signal transduction, and induced cell resistant reaction. NO could increase antioxidant enzymes activities, increase secondary metabolism substance contents, reduce cell membrane peroxidation to improve T. chinensis var. mairei seedlings resistance under enhanced UV-B stress. Therefore, applying appropriate concentration of exogenous NO can effectively reduce UV-B stress damage on T. chinensis var. mairei seedlings.