THE ACCUMULATION OF SOLUTES AND WATER BINDING STRENGTH IN DURUM-WHEAT

Variations in water binding strength, water relations and the accumula tion of solutes during water stress of three durum wheat (Triticum dur um Desf.) cultivars are reported and discussed. Water binding strength was determined by constructing adsorption isotherms at 5 and 20 degre es C and by calculating the differential enthalpy (Delta H) after van' t Hoff. Reducing sugars, proline, K+ and Cl- were the major contributo rs to osmotic adjustment. Solutes, such as quaternary ammonium compoun ds, and non-reducing sugars contributed to osmotic potential at full t urgor, but did not increase in proportion to water stress. Genotypic d ifferences have been observed for KC accumulation capability, the wate r-stressed leaves of cv. Capeiti 8 showing the largest increase. The s ame cultivar demonstrated the most negative Delta H values, indicative of strongly bound water, and the highest integrated enthalpy (Delta H -int) 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 c harged groups of macromolecules. The accumulation of ions (Cl-, K+) an d proline was concurrent with an increase in the binding-strength of t ightly and weakly bound water, respectively.