Overexpression of BvNHX1, a novel tonoplast Na+/H+ antiporter gene from sugar beet (Beta vulgaris), confers enhanced salt tolerance in transgenic tobacco

Salinity is one of the major environmental factors that limit the plant growth and crop productivity worldwide. Tonoplast Na⁺/H⁺ transporters (NHXs) play crucial roles in regulating the intracellular Na⁺/K⁺ and pH homoeostasis, which is essential for salt tolerance and development of plants. In the present study, a novel gene BvNHX1 encoding tonoplast Na⁺/H⁺ antiporter was isolated in natrophilic crop sugar beet (Beta vulgaris) and functionally characterized in tobacco (Nicotiana tabacum) plants to assess the behavior of the transgenic organisms in the response to salt stress. The results showed that overexpression of BvNHX1 significantly enhanced salt tolerance in transgenic tobacco plants compared with wild-type (WT) plants. The seed germination, root length, plant height, and fresh and dry weights in transgenic plants were significantly higher than those in WT plants under salt stresses. The contents of leaf relative water, chlorophyll, proline, soluble sugars, and soluble proteins were significantly higher as compared with WT plants, while malondialdehyde (MDA) contents were significantly lower than those of WT plants under salt stresses. Na⁺ and K⁺ contents both in shoots and roots of transgenic plants were significantly higher than those of WT plants, and transgenic plants maintained a balanced K⁺/Na⁺ ratio under saline conditions. Taken together, these results suggested that overexpression of BvNHX1 reduced damage to cell membrane by reducing osmotic potential of cells, and maintaining relative water and chlorophyll contents of leaves, and finally improved salt tolerance in transgenic tobacco plants.