Differences for bound water content as estimated by pressure–volume and adsorption isotherm curves

Abstract

Pressure–volume ( PV) and adsorption isotherm (AI) curves were constructed on fresh and dry tissues of durum wheat respectively, to assess the relation between the water status of living leaves and the properties of water that is bound (BW) with different strength to ionic, polar or hydrophobic sites of macromolecules. The leaves were collected from six genotypes grown in field, in 2 years. The amounts of the non-osmotic BW fraction, free water and osmotic potential at full turgor were determined by pressure–volume ( PV) curves. Three parameters that relate to the amounts of the weakly and strongly bound water (quantitative BW properties) and five parameters related to tissues-binding strength for the same water fractions (qualitative BW properties) were calculated by AI-curves. The non-osmotic volume of PV-curves doesn’t correspond to the water fraction bound to the charged or polar sites of macromolecules as determined by AI-curves. The qualitative parameters, in contrast to quantitative parameters, may be affected by common physical-chemical factors: the changes in the amount of strongly bound water in tissues were independent from those in the weakly bound fraction; in contrast an increase in tissue affinity for strongly bound water implied a simultaneous increase in the affinity for weakly bound water. The qualitative properties of bound water may be particularly important for drought adaptation in durum wheat, being associated with the solute potential and with the succulence degree of the leaves.