Overexpression of Suaeda salsa SsNHX1 gene enhanced salt and drought tolerance of transgenic tobacco

Tobacco (Nicotiana tobacum L.) is an important economic and model plant. Salt and drought are two important environmental factors that are harmful to plant growth, development, production and quality of tobacco. In addition to conventional salt and drought prevention measures, genetic engineering of plants has also been proven to be effective. In order to improve salt and drought tolerance of tobacco, Na⁺/H⁺ anti-porter gene SsNHX1 was cloned from Suaeda salsa salt-tolerant plant and overexpressed in tobacco by agrobacterium-mediated genetic transformation. The differences in salt tolerance and drought resistance were compared by determining phenotypic and physiological indexes of wild and transgenic tobacco L1 and L5. Phenotypic analysis showed that salt tolerance of SsNHX1 transgenic tobacco lines L1 and L5 were significantly higher than that of the wild type. This was evident from the vigorously growth and uninhibited root elongation under salt stress condition. The overexpressed transgenic lines of tobacco accumulated more Na⁺ and K⁺ in the both leaves and roots and with faster rate of increase of Na⁺ and slower decreasing rate of K⁺. The lines also maintained significantly higher contents of relative leaf water and chlorophyll, but lower malondialdehyde contents and relative conductivities. The results indicated that overexpression of SsNHX1 gene apparently promoted compartmentalization of Na⁺ from vacuolar cells into vacuoles and improved salt tolerance of transgenic plants of tobacco. On the other hand, SsNHX1 transgenic tobacco plants showed significant enhancement of drought tolerance than the wild type and restored normal growth after rehydration. Under drought stress, the contents of malondialdehyde and relative conductivities of transgenic lines were lower than those of the wild type, while the relative water and chlorophyll contents of leaves were maintained. The results suggested that under drought stress, overexpressed SsNHX1 in tobacco reduced damage to cell membrane by reducing osmotic potential of cells, maintaining relative water and chlorophyll content of leaves, and finally improved drought resistance of tobacco.