Physiological Response Of Lespedeza Formosa Under Enhanced UV-B Radiation And Drought Stresses

The greenhouse effect induced by the global climate change has significant influence onplant growth and metabolism, the depletion of O3has been resulting UV-B enhancement andmeanwhile the global warming deteriorates drought-stressed environment, so plants will bemore seriously affected by enhanced UV-B radiation and drought stress. The physiologicalresponses of plants to enhanced UV-B radiation or drought stress have been extensive andin-depth study, and get many valuable research achievements. However, the previous study ofplant physiological response to enhanced UV-B radiation and drought stress has followingdeficiencies:(1) Crops are the main research materials, but studies of other types of plant arefew.(2) Most of previous studies are mainly regard to single environmental factor stress, butfew regard to combined-stresses of many environmental factors.(3) Previous studies aremainly regard to one class of indicators, but lack of systematic research of many indicators inplant.Pot cultivation experiments were conducted to study the effects of enhanced UV-Bradiations and drought stress on the content variation of photosynthetic pigments,UV-absorbing compounds, adjusting osmotic substances and the activity of antioxidantenzymes in the leaves of Lespedeza Formosa, attempt to explore the physiological andbiochemical mechanism of Lespedeza Formosa in resisting enhanced UV-B radiation anddrought stress, and the interaction effect between UV-B and drought, in order to provide thetheoretical basis to thoroughly revealing the physiological mechanisms of Lespedeza Formosaresistance to abiotic stresses.The main conclusions are as follows:1. Low-intensity UV-B radiation induced the synthesis of the chlorophyll and carotenoid,however high-intensity UV-B radiation inhibited the synthesis of the chlorophyll, and thecarotenoid contents decreased at first and then increased under high-intensity UV-B radiation;Enhanced UV-B radiation inhibited the activity of SOD and CAT, but induced the activity ofPOD and APX and the contents of MDA increased greatly; Enhanced UV-B radiation inducedthe contents of the UV-absorbing compounds significantly increased; Under enhanced UV-Bradiation, the free proline contents increased significantly, the soluble protein contents decreased at first and then increased, however, the soluble sugar contents increased underlow-intensity UV-B radiation but decreased under high-intensity UV-B radiation.2. Mild drought stress induced the synthesis of the chlorophyll and carotenoid, howeversevere drought stress inhibited the synthesis of the chlorophyll, and the carotenoid contentsincreased under the later period of severe drought stress; The contents of MDA and theactivity of antioxidant enzymes did not significantly increased under mild drought stress, butsignificantly increased under severe drought stress; Drought stress induced the contents of theUV-absorbing compounds significantly increased; Drought stress induced the contents of freeproline and soluble sugar significantly increased, but the soluble protein contents were higherthan the control group only in the mid-term of drought stress.3. Enhanced UV-B radiation and drought combined stress could ease the degradation ofchlorophyll caused by enhanced UV-B radiation, but did not work to carotenoid; Undercombined stress, the activity of SOD and CAT were higher than that under enhanced UV-Bradiation treatment, but the activity of POD and APX and the contents of MDA were lowerthan that under enhanced UV-B radiation treatment; Combined stress could induce thecontents of the UV-absorbing compounds significantly increased; Under combined stress, thesoluble protein contents were higher than that under enhanced UV-B radiation treatment,however, the low of the content varitation of free proline and soluble sugar did not obvious.4. Enhanced UV-B radiation caused damage on membrane system and photosyntheticpigment of Lespedeza Formosa, and damage was deeper with the radiation increased,Lespedeza Formosa mainly through synthetic UV-absorbing compounds and improved thePOD and APX activity to resist enhanced UV-B radiation; Lespedeza Formosa had strongadaptability for mild drought stress, but severe drought stress caused significant damage onLespedeza Formosa, Lespedeza Formosa mainly through synthetic adjusting osmoticsubstances and improved the antioxidant enzymes activity to resist drought stress; LespedezaFormosa existed cross adaptation to enhanced UV-B radiation and drought stress, enhancedUV-B radiation and drought combined stress could alleviate the damage caused by enhancedUV-B radiation, it was mainly because combined stress could induce the contents of theUV-absorbing compounds significantly increased and increase the coordination of antioxidantenzymes.