Effects of transpiration on sodium accumulation in the shoots of winter wheat under salt stress

Hydroponic experiments were performed with a kind of membrane-imperment fluorescent dye PTS, an apoplastic tracer, to investigate the relation between transpiration and sodium accumulation in the shoots of 4 different winter wheat genotypes. The results indicate that the relation varies with salt concentrations. Under lower salt（NaCl, 150 mmol/L）stress, there is not any significant correlation between transpiration rate and sodium accumulation in the shoots, while, under higher salt（NaCl, 250 mmol/L）stress, there is a significant correlation between them. The higher transpiration rate is, the more Na+ accumulation is. There is also a significant correlation between the content of PTS and sodium accumulation, especially under higher salt concentration and longer stress time. As salt concentration increased, the transpiration rate and the transpiration velocity decrease, however, the amount and the rate of sodium accumulation, and the sodium concentrations in intracellular and symplastical fluids are all increased. The longer the salt stress time, the higher the transpiration rate, the sodium accumulation amount and the intracellular sodium concentration, the lower the sodium concentration and sodium accumulation in the symplastal flow. Whether there is salt stress or not, the transpiration velocity of warm winter wheat cultivars NR9405 and Xiaoyan6 are smaller than that cold winter wheat cultivars of Shaan229 and RB6. These results indicate the lower canopy temperature of cold-type winter wheat is caused by the higher transpiration. Under higher salt stress, the bypass flow has great effect on sodium accumulation, the more the apoplastic leakage, and the more the shoot sodium accumulation. This means that higher transpiration is an adverse characteristic to wheat under salt stress.