Functional Analysis Of A Vacuolar Na~+/H~+ Antiporter Gene OsNHX2 From Rice (Oryza Sativa L.)

Rice(Oryza sativa L.) is one of the most important crops that is cultivated worldwide.As it has low salt tolerance,and its production and planting area are greatly affected by soil salinity.It is a long-term goal to analyze the mechanism and improve the salt tolerance of rice.Na⁺/H⁺ antiporters,which catalyze exchange of Na⁺ for H⁺ across membranes,are ubiquitous membrane proteins that play important roles in cellular pH and Na⁺ homeostasis throughout the bilogical kingdom.They are located in both plasma and vacuolar membranes,removing Na⁺ from the cytosol or compartmentalizing it in vacuoles for maintenance of a low Na⁺ concentration.In particular,the vacuolar Na⁺/H⁺ antiporter has been investigated and proposed to play an imprortant role in salt tolerance.This thesis aims to functional analysis of a vacuolar Na⁺/H⁺ antiporter gene from rice through transgenic way.The are given as follows.We constructed two plant expression vectors respectively carrying sense or antisense rice OsNHX2 gene under the regulation of cauliflower mosaic virus 35s promoter.The mature embryo derived calli were infected by Agrobacterium tumefaciens EHA105 with pCAM-OsNHX2 or pCAM-AsOsNHX2,from which hygromycin resistant plants were obtained.PCR identification proved that the OsNHX2 or AsOsNHX2 was integrated into the genomes of the rice plants.We found that the sense OsNHX2 transgenic plants s22 were significant from non-transgenic plants in several agronomy traits,such as spike length,grain length and width and grain density and so on.RT-PCR analysis confirmed that OsNHX2 in the transgenic plants carrying sense OsNHX2 gene was overexpressed and that carrying antisense gene was depressed.In addition,under 150 mM NaCl stress,there was no marked difference in phenotype between T₂ sense OsNHX2 transgenic plants and nontransgenic plants,but they were better than antisense OsNHX2 transgenic plants. Under 300 mM NaCl stress,the plant fresh weight,relative water and the content of chlorophyll,soluble sugar and K⁺/Na⁺ ratio in leaves of sense OsNHX2 transgenic plants were higher than those in antisense OsNHX2 transgenic and non-transgenic plants.The overexpression of OsNHX2 gene may enhance the salt tolerance of rice.