Regulation Of Polyamine Metabolism And Its Relation To Salt Tolerance And Signal Transduction In Plants

Salt stress affects every aspect of physiology in crops, as a result virtually reduces their productivity. One of strategies for agriculture is to improve the salt tolerance of crops. As adaptive response, plants can effectively adjust their physiology and metabolism to reduce stress injury. Polyamines, mainly Put, Spd and Spm, response not only to adverse conditions but signal transduction in higher plants. However, the mechanism is still not well established in the relationships between polyamine forms (free, PCA soluble and PCA insoluble) and salt tolerance, moreover, whether polyamine participate the stress signaling remains unclear. Therefore, two barley cultivars (Hordewn vulgare L.) differing in salt tolerance (J4, salt-tolerance; KP7, salt-sensitive), and polyamine biosynthesis inhibitors D-Arg, DFMO, MGBG and CHA, which inhibits arginine decarboxylase (ADC), ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC) and spermidine synthase respectively, polyamines, glycine betaine (GB) and CaCl2 were utilized to study the relationships between polyamine metabolism and salt tolerance. Meanwhile, maize (Zea mays L cv nongda 108, VP line MIA4, VP5/VP5), ABA biosynthesis inhibitor Tungstate and PAO inhibitor Guazatine were also employed to investigate the roles of polyamines in stress signaling.The result indicated that the conversion of Put to Spd and Spm was provoked in barley roots by NaCl (0-300 mmol/L) treatment. Due to the increase of Spd and Spm contents, the ratio of (Spd+Spm)/Put was obviously enhanced. D-Arg, DFMO and MGBG treatments not only reduced the polyamine levels and the conversion of Put to Spd and Spm, but further injured the salt stressed seedlings. However the injury was obviously ameliorated by exogenous GB. GB (1 mmol/L) treatment increased the polyamine levels and the conversion ofPut to Spd and Spm in the barley roots under salt stress, thus, it also enhanced the ratio of (Spd+Spm)/Put. These results indicated that the higher ratio of (Spd+Spm)/Put was advantageous to plant salt tolerance.Salt stress caused the decrease of PCA soluble and insoluble conjugated polyamines levels in barley roots. As one part of conjugated polyamines, cell wall residue (CWR) conjugated polyamines in the roots also decreased under salt stress, and exogenous calcium treatment could effectively reverse this effect. Calcium treatment also reduced the injury caused by salt stress, and resulted in the increase of free polyamines in apoplast as well as conjugated polyamines in soluble proteins in roots of barley seedlings as compared with thecontrol of salt stress.Exogenous polyamines ameliorated the salt stress injury and caused the increase in activities of SOD, CAT and POD in barley roots under salt stress. Such treatments also caused the decrease of the rate of 0~2 production, but resulted in the accumulation of AsA compared with the control of salt treatment. Plasma membrane and tonoplast H+-ATPase, which regulates the ion and pH balance, were significantly activated by polyamine treatments, as the result, the ration of K+/Na+ increased and the ion homeostasis were reestablished in barley roots. Exogenous polyamine treatments also increased the conjugated polyamine levels in chloroplast of maize seedlings under salt stress. As compared with salt stress, the PS1I primarily chemical efficiency (Fv/Fm) and net photosynthetic rate also enhanced under polyamine treatment. These results showed that exogenous polyamines had a protective effect on plants subjected to salt stress.In leaves of maize seedlings, polyamine content increased significantly after 24h of exogenous ABA and salt stress treatments. Salt stress also led to an increase in the endogenous ABA level. We used ABA deficient mutant (VP5/FP5) and ABA biosynthesis inhibitor tungstate to reduce ABA production, which resulted in the reduction in polyamine content compared with the control of salt stress. The polyamine synthesis inhibitors D-Arg and DFMO also reduced the polyamine content in leaves of maize seedling under salt st...