Abstract
Regulation of water permeability of plasma-membrane (Pf1) and vacuolar-membrane (Pf2) is important for plant growth, water supply from root to shoot, and survival under drought condition. To understand how Pf1 and Pf2 should be regulated for satisfying these different demands, a three-compartment model which we developed previously, was used for simulating swelling/shrinking of a protoplast in response to osmotic changes. The results indicate that: (1) In a mature cell with large central vacuole, high values of both Pf1 and Pf2 are required for quick cell-enlargement, and for quick water transport across the cell. By contrast, whole-cell dehydration can be delayed most effectively when both Pf1 and Pf2 are low, but severe dehydration from the cytoplasm can be avoided when Pf1 is low and Pf2 is high. (2) In a young cell which has smaller vacuole, only Pf1 but not Pf2 is important for the optimal adjustment of cell water relations.
