Alteration of Cell-Wall Water Content and Elasticity in Douglas-Fir during Periods of Water Deficit.

Three populations of seedlings of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) were subjected to recurrent drought cycles. Pressure-volume curves were developed to derive the osmotic and pressure potentials as functions of the symplastic water over a wide range of relative water content. The drought cycles induced large reversible changes in the relative water content of the apoplasm and in the bulk modulus of elasticity. These responses have not been reported previously in any species of higher plant. Our data suggest that turgor regulation in Douglas-fir is mediated by structural and biochemical factors associated with the cell wall, rather than by osmotic adjustment.