Comparative Study On Root Water Uptake In Solanum Pimpinellifolium And Solanum Lycopersicum Under Salt Stress

Salt stress is one of the major abiotic factors affecting plant growth and development,and it almost affects all of the important physiological activities in plants especially water physiology. Under stress, plants can maintain water balance by regulating the relationship between water uptake and water loss. However, the regulatory strategy still remains to be elucidated in tomato genotypes with different tolerance. In this research, using wild tomato genotype L03708(L03708 for short) and cultivated tomato genotype M82(M82 for short) as experimental materials, the growth, ion uptake, water metabolism and the regulatory mechanism were preliminarily studied under salt stress(150 m M Na Cl). The main results were as follows:1. Under salt stress, the dry weight accumulations of shoots and roots in M82 were obviously inhibited, and the net photosynthetic rate, stomatal conductance and transpiration rate were decreased significantly(nearly 50%); while those in L03708 were not affected significantly, which indicate that there were differences in terms of growth between the genotypes with different salt tolerance.2. Na+ as well as Na+/K+ of shoots in L03708 and M82 differed under control conditions.After salt treatment, the Na+level of shoots and roots was increased significantly in both genotypes, and it was increased more in M82. In L03708, the Na+ translocation coefficient rose considerably, causing Na+ in shoots to increase significantly, and the Na+ was likely to be transferred to the vacuole for osmotic adjustment.3. Under salt stress, unlike those in M82, the root and leaf hydraulic conductivities in L03708 did not decline precipitously, especially the root hydraulic conductivity, which showed no significant difference compared with the control. The results indicate that L03708 had stable ability to absorb and transport water.4. Plasma membrane aquaporins were involved in root hydraulic conductivity at both transcript and protein levels, and different PIPs in different genotypes responded variously. At transcript level, the root PIPs in L03708 were up-regulated or not changed obviously compared with the control, while most of the PIPs were down-regulated in M82. At proteinlevel, the PIP1 protein abundances were increased and the PIP2 protein abundances were decreased in L02708. However, both PIP1 and PIP2 protein abundances were decreased in M82.5. Under salt stress, there existed an obvious difference in root oxidative damage between two tomato genotypes. In the root of M82, the hydrogen peroxide content and relative electrolyte leakage were increased and the oxidative damage was more serious.L03708 may have higher antioxidant defense ability, thus effectively preventing membrane lipid peroxidation and maintaining the membrane integrity.6. Exogenous hydrogen peroxide decreased the root hydraulic conductivity and increased the root relative electrolyte leakage in both genotypes, but the effects in L03708 was slighter.The PIP1 protein abundances were significantly increased in L03708 but decreased in M82.The results showed that membrane oxidative damage may have some relationship with water uptake.In conclusion, the regulatory strategy of water balance in different tomato genotypes differs greatly, which may be the physiological basis for the different tolerance. A major cause of the different water metabolism is the difference in plasma membrane damage under salt stress resulted from different antioxidant defense ability, and membrane damage may affect the water metabolism in plants by affecting the aquaporin expression or activity.