Study of wheat ( Triticum aestivum L.) seed rehydration observed by the Dent generalized model and 1H-NMR relaxometry

The early stages of winter wheat (Triticum aestivum L.) seed hydration were monitored in order to improve our understanding of the molecular mechanisms of drought resistance. Investigations were carried out using gaseous phase hydration kinetics, sorption isotherm, and H-1-NMR relaxometry. Hydration kinetics have shown that the mass increase could be fitted with a single exponential function. Two fractions of bound water were distinguished: very tightly bound water, Delta m/m(0) = 0.082 +/- 0.016, and the tightly bound water fraction, Delta m/m(0) = 0.048 +/- 0.033, with a hydration time t (h)(1) = (62 +/- 23) h. The standard Dent's model which was used to fit the experimental data, was successfully applied but only for values of relative humidity smaller than h < 0.9. The sorption isotherm was better fitted using the generalized Dent's model, with the value of the b parameter equal to 0.947, the mass of the water saturating primary water binding sites equal to Delta M/m(0) = 0.0209, and the fraction of unoccupied binding sites at h = 1 equal to 1/b(1) = 0.104%. Proton free induction decays regi-stered for dry samples up to hydration level Delta m/m(0) = 0.128 were better described by the Abragam function, whereas for a higher hydration level the Gaussian function sufficiently described the proton signal of the samples.