Overexpression of Suaeda salsa stroma ascorbate peroxidase in Arabidopsis chloroplasts enhances salt tolerance of plants

To clarify the contribution of the stroma ascorbate peroxidase (sAPX) to the protection against salt-induced oxidative stress, we cloned the stromal APX from the euhalophyte Suaeda salsa (Ss.sAPX) for transfer into Arabidopsis. Confocal and RNA blotting analyses showed that the foreign gene was integrated into the Arabidopsis genome and located in chloroplasts. Measurements of isolated chloroplasts indicated that total APX and stromal APX activity were significantly higher in the transgenic plants than in wild-type (WT) plants but that thylakoid APX activity was not altered. The overexpression of Ss.sAPX in Arabidopsis increased the germination rate, cotyledon growth, survival rate, and tolerance to salt stress. Under NaCl stress, the transgenic plants had longer roots, higher total chlorophyll content, higher total APX activity, less cell membrane damage (as indicated by MDA levels), and lower H2O2 content than the WT. Moreover, under either normal or NaCl-stress conditions, sodium and proline contents and SOD and CAT activities did not differ between transgenic and WT plants. SOD and CAT activities in all tested lines declined gradually under salt stress. These results suggest that Ss.sAPX can play an important role in the protection against salt-induced oxidative stress in higher plants.

► The deduced amino acid sequence of Ss.sAPX is closest to that of M. crystallinum.
► Ss.sAPX is exclusively localized in chloroplasts of transgenic Arabidopsis.
► sAPX activity is higher in the chloroplasts of transgenic plants than in WT.
► H2O2 and MDA content is lower in transgenic plants than in WT under salt stress.
► Overexpression of Ss.sAPX enhances salt tolerance by maintaining a low level of H2O2.