THE RELATIONSHIP BETWEEN CARBON AND WATER TRANSPORT IN SINGLE CELLS OF CHARA-CORALLINA

The hydraulic resistance of the plasma membrane was measured on single internodal cells of Chara corallina using the method of transcellular osmosis. The hydraulic resistance of the plasma membrane of high CO2- grown cells was significantly higher than the hydraulic resistance of the plasma membrane in low CO2-grown cells. Therefore we tested the po ssibility that the ''bicarbonate transport system'', postulated to be present in low CO2-grown cells, serves as a water channel that lowers the hydraulic resistance of the plasma membrane. We were unable to fin d any correlation between agents that inhibited the ''bicarbonate tran sport system'' and agents that increased the hydraulic resistance of l ow CO2-grown cells. We did, however, find a correlation between the pe rmeability of the cell to water and CO2. We propose that the reduced h ydraulic resistance of the plasma membrane of the low CO2-grown cells is a function of a change in either the structural properties of the l ipid bilayer or the activity of a CO2 transport protein so that under conditions of reduced inorganic carbon, the plasma membrane becomes mo re permeable to CO2, and consequently to other small molecules, includ ing H2O, methanol and ethanol.