Seawater-irrigation effects on growth, ion concentration, and photosynthesis of transgenic poplar overexpressing the Na+/H+ antiporter AtNHX1

Tonoplast Na+/H+ antiporters increase the salt resistance of various plant species, but very little is known about the role of these antiporters in the salt resistance of trees. Understanding the physiological responses of plants to salinity stress is of paramount importance in examining the salt resistance of transgenic plants. In this study, the wild-type poplar (WT; Populus x euramericana var. Neva) and its transgenic varieties (TR) that overexpress the AtNHX1 gene were exposed to various seawater concentrations (0%, 10%, 20%, and 30%) for 30 d to determine the effects of seawater on seedling growth, ion content, and photosynthetic productivity. Results show that TR plants grew much better than WT under saline conditions. Differences between WT and TR in most parameters were significant after 30 d exposure to 20% and 30% seawater concentrations. The dry weight of TR was higher than that of WT for each seawater treatment. Transgenic variety was able to maintain higher photosynthetic ability than WT upon exposure to salinity and maintained higher K+ concentrations and K+ : Na+ ratio but had less Cl(-)compared with WT. This suggests that AtNHX1 has a critical role in the regulation of K+ homeostasis, which in turn affects plant K+ nutrition and salt resistance.