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 possibility 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 find any correlation between agents that inhibited the "bicarbonate transport system" and agents that increased the hydraulic resistance of low CO₂-grown cells. We did, however, find a correlation between the permeability of the cell to water and CO₂. We propose that the reduced hydraulic resistance of the plasma membrane of the low CO₂-grown cells is a function of a change in either the structural properties of the lipid bilayer or the activity of a CO₂ transport protein so that under conditions of reduced inorganic carbon, the plasma membrane becomes more permeable to CO₂, and consequently to other small molecules, including H₂O, methanol and ethanol.