Osmotic and ionic stress effects of high NaCl concentration on seedlings of four wheat(Tritium aestivum L.)genotypes
盐胁迫下不同基因型冬小麦渗透及离子的毒害效应

The osmotic and ionic effects of salt stress on seedlings of four winter wheat genotypes were investigated using a split-root system with hydroponic solutions. The four genotypes differed in canopy temperature and included a warm canopy temperature genotype (NR 9405), a medium to cold canopy temperature genotype (Xiaoyan 6), and two cold canopy temperature genotypes (Shaan 229 and RB 6). Seeds of similar size and vigor were chosen, sterilized with 10% Javel water, and then placed on a floating mesh in distilled water to germinate in the dark. At the two-leaf stage, uniformly sized seedlings were transplanted to the split-root system, with roots from each seedling uniformly divided between the two sides of the baffle. There were 15 plants per pot. The basic culture solution was 1/2 Hoagland's nutrient solution.There were five treatments: T1: 0/0 (T1-1/T1-2); T2: PEG-6000/PEG-6000 (T2-1/T2-2); T3: NaCl/NaCl (T3-1/T3-2); T4: 0/NaCl (T4-1/T4-2); T5: PEG-6000/NaCl (T5-1/T5-2). The concentration of the NaCl solution was 200 mmol/L. The concentration of the PEG-6000 solution was 274.09 g/L. The water potential of the PEG-6000 solution was 0.88 MPa and was similar to the 200 mmol/L NaCl solution. Each treatment was replicated three times. Overall, the results showed that salt stress had both osmotic and ionic effects on the seedlings. The osmotic effect was rapid and occurred in 1 or 2 days, but the ionic effect developed more slowly, occurring after about 3 to 4 days when Na+ accumulation reached a threshold level. In T4, half of the root system was treated with Hoagland solution containing 200 mmol/L NaCl while the other half of the root system was in Hoagland's solution without salt stress. The results showed that salt stress had no significant osmotic effect on the wheat seedlings. There was no significant inhibition of leaf growth when Na+ levels within the shoots were below toxic levels. In the NaCl treatment (T3), the Na+ accumulation rate and accumlation amount were less for NR 9405 (warm) compared to the other three genotypes. The rate of Na+ accumulation decreased when the Na concentration in one cell was significantly reduced (T5). The reduction in accumulation rate was greater for NR 9405, Shaan 229, and Xiaoyan 6 than for RB 6. An increase in water potential on one side of the baffle (T4) significantly reduced the Na+ accumulation rate in NR 9405 and Xiaoyan 6. Furthermore, the Na+ content of NR 9405 and Xiaoyan 6 was significantly lower than Shaan 229 and RB 6. This suggested significant variation in water regulation and salt absorption capacity among wheat genotypes with different canopy temperatures. Specifically, warm canopy temperature genotypes had greater water regulation ability and salt absorption capacity than cold temperature genotypes. The Na+ concentration of the solution in the cell with no NaCl increased significantly during the experiment, which indicated that part of the Na+ absorbed by the plants could be recycled through t