A Novel Approach to the Water Uptake Dynamics in Roots of Maize, Wheat and Barley Under Salt Stress

The water uptake dynamics in maize, wheat, and barley under salt stress were investigated with a xylem pressure probe. The average xylem pressure responses to salt stress in the three plants were 36, 93, and 89% of the osmotic stresses for maize, wheat, and barley, respectively, which are significantly smaller than the magnitude of the osmotic stresses being applied. In order to explain the thermodynamic discrepancies among the water potential changes in the root xylem of the three plants, a novel approach, tentatively named the "symplastic flow dilution model" was proposed in this paper. The model was presented in an attempt to give answers to the problem of how the roots under salt stress could absorb water when the water potential of the xylem sap is considerably higher than that of the solution in the root ambient. According to the model, the salt solution in the microenvironment of the endodermis of a root was diluted to some extent by the efflux from cells so the central stele of the root is not exposed to the same solution bathing the root with the same salt concentration. In contrast, we also presented another approach, the "reflection coefficient progression approach", which was less likely to be true because it requires a considerable amount of solute to be transported into the root xylem when the salt stress is severe.