Abstract: To identify cell salt tolerant ability generated by cytosolic ascorbate peroxidase (cAPX) from rice(Oryza sativa L.), two encoding genes, OsAPXa and OsAPXb(GenBank accession nos. D45423 and AB053297, respectively) were introduced into tobacco(Nictiana tabacum, N.plum), respectively. Southern blot confirmed that the two genes were integrated into genome of N.tabacum, respectively. Moreover, Northern blot further revealed that foreign genes effectively expressed in vitro. OsAPXa/b transgenic N.tabacum progeny T₁, T₂ generation were identified and assayed further. Under the carbonate stress, the T₂ independent homozygous transgenic lines showed the elevated activity of APX, the lower H₂O₂, and the lower ion leakage than that in wild type plants. Surprisingly, T₂ generation seedlings could survive on MS medium containing either 10 mmol·L^-1 NaHCO₃ or 5 mmol·L^-1 Na₂CO₃, just along with the retarded growth of root and yellowish leaf, whereas the wild type plants even could not grow under lower carbonate stress. Our results suggested that transgenic tobacco expressing cytosolic OsAPXs improved cell salt tolerance; both cytosolic OsAPXs played the crucial roles, especially in response to carbonate stress.

Key words: cytosolic ascorbate peroxidase(cAPX), carbonate, rice(Oryza sativa L.), salt tolerance, transgenic tobacco(Nictiana tabacum, N.plum)