Study On Effects Of Polyamine On Drought Tolerance Mechanism Of Phyllostachys Edulis Seedling

Polyamines (PAs) are low molecular nitrogen-containing compounds belonging to nitric fatty group, which perform particular physiological activi-ties. Polyamines, ubiquitous in living cells, are evolutionarily highly conserved organic cationic polymer and have important functions in the regulation of abiotic stress tolerance. Seedlings of phyllostachys edulis have been used as experimental materials and PEG6000as osmotic regulator to simulate the effect of drought stress. By applying exogenous polyamines and polyamines synthesis inhibitor under drought stress condition, this thesis analyzed genetic expression of drought resistance gene transcription factor, genes of key enzymes that control polyamines synthesis, the changes of endogenous polyamines and physiological and biochemical characteristics of drought resistance of seedlings of phyllostachys edulis to clarify the regulation mechanism of polyamine to drought resistance in seedlings of phyllostachys edulis. The main results and conclusions care as follows:1. Under normal conditions, the Put content of seedling of phyllostachys edulis was higher than the content of the Spd and Spm, which was1.07times of the Spd and1.16times of the Spm. Under drought stress conditions, the Put content dropped significantly, whilst Spm and Spd increased first and then decreased but but contents of Spm and Spd were still significantly higher than control level. After applying0.1mM exogenous Spd, seedlings accumulated maximum endogenous Put, Spd and Spm reaching0.0247、0.0395and0.04661mg per gram in fresh weight, which was significantly higher than other treatments of concentration.By applying polyamines synthesis inhibitor, endogenous Put,Spd and Spm contents of seedling of phyllostachys edulis had downward trends and1mM MGBG significantly inhibit the synthesis of endogenous Put and Spm, Spd. The results show that the SAMDC is the key enzyme of polyamines synthesis in seedling of phyllostachys edulis, various types of polyamines can convert each other under drought stress:Endogenous Put was converted to Spd and Spm and exogenous Spd content of0.1mM could obviously improve the levels of endogenous Put, Spd and Spm of seedling of phyllostachys edulis.2. Under drought condition, content of chlorophyll (a+b) and Chla/Chlb were significantly inhibited, actual photochemical efficiency Yield and qP significantly decreased, while NPQ improved significantly. Application of exogenous0.5mM Spd could significantly increase the content of chlorophyll and carotenoids and improve actual photochemical efficiency Yield and qP.1.0mM MGBG could significantly reduce the content of all kinds of pigments. The results show that under drought stress,polyamines could raise the levels of photosynthetic pigments of seedling of phyllostachys edulis, improve photosynthetic performance, improve the capacity of drought resistance.3. With the strengthening of drought stress, Proline content continued to rise, whilst soluble protein, SOD、POD and CAT increased first and then decreased. Leaf relative water content decreased gradually and generation rate of super oxygen free radical increased,which reached67.85μmol·min-1·g-1under treatment of25%PEG.The generation rate is1.48times to control and reached a significant level. The cell membrane lipid peroxidation was enhanced and leaf relative conductivity and MDA content in the cell membrane also gradually improved lipid peroxidation as well.Under drought stress of20%PEG, Application of exogenous0.5mM Spd could significantly increase content of soluble protein and activity of SOD、POD and CAT, while content of Pro decreased significantly. Application of exogenous0.5mM Spd maximized the leaf relative water content. Generation rate of oxygen free radical reached45.33μmol·min-1·g-1, which decreased to75.68%of control and significant difference to control. This shows that application of exogenous0.5mM Spd decreased of membrane lipid peroxidation under drought stress. Application of exogenous1mM MGBG could significantly decrease content of soluble protein and activity of SOD、POD and CAT, while content of Pro increased significantly. Generation rate of oxygen free radical reached64.77μmol-min-1·g-1and the content of increased significantly. Results show that under drought stress polyamines can improve the ability of drought resistance of seedling of phyllostachys edulis through increase content of soluble protein and activity of SOD、POD and CAT and there is competition between proline synthesis and endogenous polyamines of seedling of phyllostachys edulis.4. The lenght of cDNA fragment from cloning SAMDC of seedling of phyllostachys edulis is1200bp. The sequence of the cDNA fragment is significant different to that from animal SAMDC. which shows high heterogeneity. To plants such as arabidopsis thaliana, rice and corn, the gene homology reaches75%or more,which is very conservative on the evolution of the species. Secondary structure of SAMDC gene of phyllostachys edulis is mainly random coil, which takes55.4%of secondary structure. Then α-helix takes20.1%and β-angle distribution area is24.6%. Tertiary structure and secondary structure of encoding protein coincide with the theory predicts and are Similar to the predictions of SAMDC protein of a variety of other plants.5. The express of SAMDC gene raised under drought stress. With the increase of applying concentration of exogenous Spd, SAMDC expression was significantly decreased, reaching the lowest point with treatment of0.5mM exogenous Spd. Polyamines synthesis competitive inhibitor spermine (D or L) could restrain the expression of SAMDC, but MGBG was significantly inhibit SAMDC’s expression, this function is consistent with MGBG’s characteristic which is SAMDC’s inhibitors. The results also show that Seedling of Phyllostachys edulis can actively absorbed from exogenous polyamines to improve the drought-resistant ability.6. The express of DREB gene raised under drought stress, when exogenous Spd level of less than or beyond0.5mM, the Spd concentration with DRED2expression quantity and have a negatively correlated,but at the0.5mM. DREB2has a high expression significantly. Three kinds of polyamines synthesis inhibitor L-ARG, D-ARG. MGBG significantly reduce DREB2’s expression level. It turned out that DREB2is transcription factor of seedling of phyllostachys edulis to fight with the drought. Low concentration of the Spd could ease the Seedling of Phyllostachys edulis drought stress, the amount of DREB2’s express was dropped. But relatively high concentrations of the Spd may play the role of drought stress signaling and promote the expression of DREB2.