Characterization of Solute Efflux from Dehydration Injured Soybean (Glycine max L. Merr) Seeds

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Abstract
Soybean (G. max L. Merr) seeds lose their tolerance of dehydration between 6-36 h of imbibition. Soybean axes and cotyledons were excised 6 h (tolerant of dehydration) and 36 h (susceptible) after commencing imbibition and subsequently dehydrated to 10% moisture. Kinetics of the efflux of K, phosphate, amino acid, sugar, protein and total electrolytes were compared in the 4 treatments during rehydration. Only slight differences were observed in the kinetics of solute efflux between the 2 cotyledon treatments dehydrated at 6 and 36 h suggesting that the cotyledons may retain their tolerance of dehydration at this stage of germination. Several symptoms of injury were observed in the axes dehydrated at 36 h. An increase in the initial leakage of solutes during rehydration, as quantified by the .gamma.-intercept of the linear regression line for solute efflux between 2 and 8 h suggests an increased incidence of cell rupture. An increase in the rate of solute efflux (slope of regression line between 2-8 h) from fully rehydrated axes were observed in comparison to axes dehydrated at 6 h. The Arrhenius activation energy for K, phosphate and amino acid efflux decreased and for protein remained unchanged. Both observations indicate an increase in membrane permeability in dehydration-injured tissue. Increasing the H+ concentration of the external solution increased K+ efflux from both control and dehydrated/rehydrated samples, increased sugar efflux from axes at 6 h imbibition but decreased sugar efflux from axes at 36 h imbibition, indicating changes in membrane properties during germination. The dehydration treatment did not alter the pattern of the pH response of axes dehydrated at 6 or 36 h but did increase the quantity of K and sugar eflux from dehydration injured axes. These results are interpreted as indicating that dehydration of soybean axes at 36 h of imbibition increased both the incidence of cell rupture during rehydration and altered membrane permeability of the rehydrated tissue.