Strategies for acclimation to seasonal drought in Ceratonia siliqua leaves

Plants of Ceratonia siliqua L. (carob tree) were subjected to a slow cycle of soil water depletion in summer and in winter. Recently mature and fully turgid leaves were squeezed in a pressure chamber in order to analyse changes in the components of water potential related to the acclimation to drought. Mathematical expressions were fitted to the primary data in order to calculate the elasticity modulus and the dependence of turgor pressure on relative osmotic water content. Osmotic and water potentials decreased significantly in leaves acclimated during the summer (about 0.7 and 0.9 MPa decrease, respectively) whereas in winter the elastic properties of the wall had changed: modulus of the non-stressed leaves was 26 MPa compared to 7.5 MPa in leaves subjected to drought stress. The results indicate that Ceratonia leaves can, to some extent, maintain turgor under situations of soil drought, using different strategies according to the season.