The accumulation of solutes and water binding strength in durum wheat

Variations in water binding strength, water relations and the accumulation of solutes during water stress of three durum wheat (Triticum durum Desf.) cultivars are reported and discussed. Water binding strength was determined by constructing adsorption isotherms at 5 and 20°C and by calculating the differential enthalpy (ΔH) after van't Hoff. Reducing sugars, proline, K+ and Cl− were the major contributors to osmotic adjustment. Solutes, such as quaternary ammonium compounds, and non‐reducing sugars contributed to osmotic potential at full turgor, but did not increase in proportion to water stress. Genotypic differences have been observed for K+ accumulation capability, the water‐stressed leaves of cv. Capeiti 8 showing the largest increase. The same cultivar demonstrated the most negative ΔH values, indicative of strongly bound water, and the highest integrated enthalpy (ΔHinf) values for leaf moisture below 0.1 g H2O per g dry weight, i.e. in the isotherm region where water was presumably chemisorbed to the charged groups of macromolecules. The accumulation of ions (Cl−, K+) and proline was concurrent with an increase in the binding‐strength of tightly and weakly bound water, respectively.