REPARTITION of WATER IN PLANT TISSUES SUBJECTED to OSMOTIC PROCESSES

A study was conducted to investigate the osmotic behavior of potato tissue in equilibrium with an osmotic medium consisting of various solutions ranging from 5% to 60% sucrose at 40°C. At equilibrium, the total volume changes of the potato tissue with respect to the initial volume were constant for a wide range of sucrose concentration of osmotic solutions (10% to 40%). In order to explain this behavior, the analysis was transposed from the global description of the entire structure to the analysis of the behavior of the cells. It was found that the cells of the potato tissue were plasmolyzed in osmotic media from 10% to 40% sucrose, that is, the protoplast of the plant cell separates from the cell wall due to the efflux of water from the cell. the extracellular volume, which comprises the cell wall and the intercellular space, increased whereas the cellular volume, which is equivalent to the protoplast, decreased to maintain a constant total volume. When the tissue was in equilibrium with highly concentrated sucrose solution (40% to 60%), a loss of the integrity of the cells seemed to happen. Using a typical composition of the potato tissue and the expressions relating the equilibrium water content of each phase to the chemical potential of water, the calculated volume changes were predicted in good agreement with the experimental volume changes of the lumped cellular volume of the tissue. Thus, from the thermodynamic approach, one can predict quantitatively the repartition of water in the tissue.