Abstract
Salinity is one of the major abiotic stresses that limit the growth and productivity of sugar beet (Beta vulgaris L.). To improve sugar beet’s salinity tolerance, the ZxNHX and ZxVP1-1 genes encoding tonoplast Na+/H+ antiporter and H+-PPase from xerophyte Zygophyllum xanthoxylum were co-expressed by Agrobacterium tumefaciens-mediated transformation. It is showed here that co-expression of ZxNHX and ZxVP1-1 confers enhanced salinity tolerance to the transformed sugar beet plants compared with the wild-type (WT) plants. The chimeric plants grew well in the presence of high salinity (400 mM NaCl), whereas WT plants displayed chlorosis and died within 8 days. Compared to WT plants, the chimeric plants co-expressing ZxNHX and ZxVP1-1 accumulated more proline, Na+ and K+ in their leaves and petioles when exposed to high salinity, which caused lower solute potential, retained more water and thus subjected to lesser cell membrane damage. Interestingly, the chimeric plants accumulated higher sucrose, glucose and fructose contents in their storage roots than WT plants in the absence or presence of high salinity. Our results suggested that co-expression of ZxNHX and ZxVP1-1 improved the osmoregulatory capacity in chimeric sugar beet through increased compartmentalization of ions into the vacuoles by enhancing the activity of proton pumps and thus mitigated Na+-toxicity for plants.
Highlights
Salinity is a major abiotic stress limiting growth and productivity of plants in many areas of the world due to increasing use of poor quality of water for irrigation and soil salinization (Munns and Tester, 2008; Rozema and Flowers, 2008; Zhang and Shi, 2013)
To validate whether the ZxNHX and ZxVP1-1 genes from xerophyte Z. xanthoxylum integrated into sugar beet genome, PCR reactions were performed with specific primers to amplify the fragments of ZxNHX and ZxVP1-1, respectively
A stable transformation efficiency of 9.95% was observed using a total of 402 plants in three different experiments generating 40 T0 chimeric sugar beet plants
Summary
Salinity is a major abiotic stress limiting growth and productivity of plants in many areas of the world due to increasing use of poor quality of water for irrigation and soil salinization (Munns and Tester, 2008; Rozema and Flowers, 2008; Zhang and Shi, 2013). Saline stress to most plant species mainly accounts for the enhancement in cytoplasmic osmotic stress and Na+-specific toxicity (Munns and Tester, 2008; Maathuis et al, 2014). Plants have evolved various adaptive strategies to cope with saline stress (Shabala, 2013; Zhang and Shi, 2013; Roy et al, 2014). One of those that plant cells employ for the alleviation of excess cytosolic Na+ is to compartmentalize Na+ into the vacuoles (Yamaguchi et al, 2013). Compartmentalization of Na+ into vacuoles protects the cytoplasm from Na+-toxicity, and allows plant to use Na+
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