Physiological Response To Salt Stress And Cloning, Expression Of Betaine Biosynthesis Related Genes In Sweet Potato

This research studied the physiological and biochemical characteristics of different tissues from various salt toleranced Sweet potato seedlings (Jixu23 and Xushu781) which including water contents of shoot and root, protected enzyme activity, lipid peroxidation, osmotic adjustment content characteristics under 200mM NaCl stress, in order to analysis the mechanism of injury and salinity tolerance. At the same time, with salt sensitive Sweet potato Xushu781 as materials, we studied the alleviative effect of different concentrations of exogenous betaine on the physiological and biochemical characteristics under NaCl stress, discussed the mechanisms of enhance salt tolerance about exogenous betaine. In addition, We cloned the genes CMO and BADH which encode two key enzymes of Sweet potato betaine biosynthetic pathway, and analyzed their expressing regulation under NaCl and drought stress. The results were as follows:(1) With the extension of NaCl stress time, the water content of two varieties of Sweet potato were decreased; while the protective enzyme:SOD,POD etc, activity increased at first then reduced; the contents of MDA, proline and betaine were continue to increased; betaine aldehyde dehydrogenase activity increased at first then reduced too. But these physiological indexes of different Sweet potato tissues of each different variations changed in different scale; the protected enzyme activity, contents of proline and betaine and betaine aldehyde dehydrogenase activity of Jixu23 changed more significant than Xushu781, while contents of water and MDA of Xushu781 more than Jixu23. The results indicate that Xushu781 injured more seriously under NaCl stress.(2) Exogenous betaine has alleviative effect to salt sensitive Sweet potato Xushu781 under NaCl stress. Exogenous betaine increased the protective enzyme activity, content of proline and betaine, betaine aldehyde dehydrogenase activity, and decreased the content of MDA. Comparing physiological indexes in different betaine concentrations and stress times, it effected obviously when its treatment time at 7d and concentration at 5 mM.(3)According to the conserved amino acid sequences of CMO cDNAs in other plants, we designed primers and first cloned a 1401bp CMO cDNAs of Sweet potato(Ipomoea batatas(L.)Lam.) using both the reverse transcription-PCR and RACE, which having a 1272 bp and encoding a 423 amino acids polypeptide. Sweet potato CMO has a typical 2Fe-2S structure domain and a SRPBCC family structures domain. Analysis of the expression of Sweet potato CMO gene, it found that the experession of Sweet potato CMO was induced by NaCl and drought stress. The expression patterns of Sweet potato CMO were different in different varieties, The expression of Jixu23 CMO reduced at first then increased, and reduced at last under NaCl and drought stress. The expression of Jixu23 CMO increased at first then reduced under NaCl stress, while reduced at first then increased under drought stress. The expression of different tissue levels were different too. The expression levels of different tissue were leaf> stem> root in Sweet potato. The expression of CMO increased obviously in all tissues under NaCl and drought stress.(4) A 1719bp BADH cDNAs of Sweet potato(Ipomoea batatas(L.)Lam.) was cloned using both the reverse transcription-PCR and RACE, which having a 1518 bp and encoding a 505 amino acids polypeptide. Sweet potato BADH has typical ALDH_F10_BADH function domain. Analysis of Sweet potato BADH gene expression, it found that the experession of Sweet potato BADH was induced by NaCl and drought stress too. The expression of Jixu23 BADH increased at first then reduced and reached peak at 12 h and 6 h under NaCl and drought stress, while The expression of Jixu23 BADH reduced at first then increased. The expression levels of different tissue were leaf>stem>root in Sweet potato.