PHYSIOLOGICAL AND BIOCHEMICAL ANALYSIS OF ASA-GSH ANTIOXIDANT SYSTEM OF SEA-ISLAND COTTON IN RESPONSE TO VERTICILLIUM DAHLIAE

Abstract

Sea-Island cotton (Gossypium barbadense) is a high-quality long-fiber cotton species and is mainly planted in southern region of Xinjiang. The primary disease is Verticillium wilt, which is caused by Verticillium dahlia affecting G. barbadense growth and development. That leads to reduction in quality and yield of the fibers and thus to the huge economic loss. AsA-GSH antioxidant system has been extensively studied and is seen as having a crucial function in plant’s response to biotic and abiotic stresses. The goal of this study is to look into the resistant mechanism of AsA-GSH antioxidant system in Gossypiumbarbadense in response to V. dahliae. The two varieties, wilt-susceptible XH17 and wilt-resistant XH24, were incubated by V991 strain of V. dahliae and the treated leaves were collected for the physiological and biochemical analysis of AsA-GSH antioxidant system. The leaves were collected at day 0, 2, 6 and 9 after fungal inoculation and the functions of related enzymes of AsA-GSH antioxidant system including Superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione re-oxidase (GR), as well as the physiological indexes of malondialdehyde (MDA) and proline were measured. The mRNA and protein expression levels of the genes of APX, dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), SOD, CAT, and GR, that constitute AsA-GSH antioxidant system, were analyzed by the transcriptomic and proteomic data. The enzyme activities of CAT, SOD, GR, and APX were found to be increased significantly after V. dahliae treatment in both XH24 and XH17. Interestingly, SOD and APX activities maintained at relative high values in wilt-resistant XH24 but a decrease in values was observed during the late stage of V. dahliae treatment in case of wilt-susceptible XH17. High proline accumulation and low MDA content were observed in wilt-resistant XH24. The results of AsA-GSH antioxidant system genes shows that four APX members of GbAPX1A, GbAPX1D, GbAPX10D, and GbAPX12A, one DHAR member GbDHAR2D, four MDHAR members of GbMDHAR1A, GbMDHAR1D, GbMDHAR3A, and GbMDHAR3D, two GR members of GbGR2A and GbGR2D, two CAT members of GbCAT1A and GbCAT1D, and six SOD members of GbCSD4A, GbCSD5A, GbCSD4D, GbCSD5D, GbMSD1D and GbMSD1A were all expressed induced accumulations significantly after V. dahliae treatment, implying their important potential functions for G. barbadense to resist V. dahliae. Generally, the protein expression and mRNA expression indicated a similar profile, while some unique expressions of these AsA-GSH antioxidant system genes were also been discovered. There were ten APX members of GbAPX1D, GbAPX2A, GbAPX2D, GbAPX3A, GbAPX3D, GbAPX6A, GbAPX6D, GbAPX8A, GbAPX12A, and GbAPX3D; all six DHAR members with the exception of GbDHAR2D; three GR members locating in A sub-genome containing GbGR 1A, GbGR 2A, and GbGR 3A; six MDAHR members including GbMDAHR1A, GbMDAHR1D, GbMDAHR3A, GbMDAHR3D, GbMDAHR4A, and GbMDAHR4D; two CAT members of GbCAT1A and GbCAT4D; as well as eight SOD members of GbCSD1A, GbCSD4A, GbCSD4D, GbCSD2A, GbMSD2D, GbMSD2D, GbMSD1A and GbMSD1D, to indicate steady high expressions. These results indicated that there exist some close link and consistency between the mRNA and protein expressions, and that the preferentially expressed proteins of AsA-GSH antioxidant system might perform important functions as enzymes to catalyze the oxidation/reduction reactions and thus to maintain the redox balance and integrity of the cells in the process of G. barbadense plants to resist V. dahliae.