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The possibility that the nature of the inhibitory effect of NaCl is different during imbibition compared to germination was investigated. Germination in both NaCl and betaine (a non-toxic solute) improved with pre-imbibition in water. Seeds imbibed in inhibitory concentrations of either solute could be induced to germinate by brief exposure to water. Electron micrographs of tissue from seeds imbibed in 0.5 kmol m-3 NaCl for 25 h showed cells identical to those in seeds imbibed in water for only 1 h, but seeds imbibed for 6 h in water exhibited many changes in ultrastructure. These results are consistent with the hypothesis that seed hydration must reach a critical value before germination can proceed, and that the inhibitory effect of NaCl is primarily osmotic in barley seeds that have not reached this hydration threshold. Although isotonic solutions of betaine and NaCl were equally inhibitory to germination, isotonic solutions of betaine and NaC1 were not equally inhibitory to continued development in seeds which had been pre-imbibed in water. Calcium ions improved both germination and plumule emergence of pre-imbibed seeds in NaCl solutions, but calcium had little effect on pre-imbibed seeds placed in betaine. Very high concentrations of NaCl or betaine inhibited germination, but did not kill dry seeds. Both solutes, on the other hand, were lethal at high concentrations to germinating seeds. NaCl killed germinating seeds more rapidly than betaine, but calcium reduced the rate of killing to nearly that of betaine. We conclude that hydrated seeds are sensitive to both osmotic and toxic effects of NaCl and that calcium mitigates the toxic effect of NaCl, but not the osmotic effect. [ABSTRACT FROM AUTHOR]

Cultivars of barley (Hordeum vulgare L.) were tested for germination sensitivity to progressively higher concentrations of salt, mannitol, and betaine. The three solutes were equally inhibitory at equal osmotic potential, but there was a consistent difference in osmotic sensitivity between two cultivars, CM-67 and Briggs (Briggs was the most sensitive). There was no difference between the two cuitivars in salt or water uptake from salt solutions during imbibition. Brief presoaking in water did not improve salt resistance, indicating that a hydration dependent decrease in membrane permeability is not involved in salt tolerance. The calcium content of Briggs was higher than CM-67. These results suggest that salt inhibits barley germination primarily by osmotic effects, and that salt influx during imbibition does not play a role in this inhibition. A hypothesis regarding salt effects on germination is discussed. [ABSTRACT FROM AUTHOR]

Freeze-fracture electron microscopy of the plasmalemma of dry cowpea radicle ceils disclosed a normal-appearing membrane with a high area density of intramembraneous particles (IMPs). Seeds imbibed in either water or salt solution exhibited decreased area density of 1MPs, but water-imbibed tissue showed the greatest decline. Mean particle size increased with hydration but not enough to suggest aggregation as the cause for this density decrease. Calculations of plasmalemma area expansion during imbibition show that such expansion can account for the decrease in IMPs per unit area in the cytoplasmic side (PF) of the membrane in water-imbibed, but not in salt-imbibed, tissue. During imbibition, there is a change in the ratio of IMPs per unit area of the PF versus EF (external) membrane faces, suggesting a relative increase in the number of EF particles. These changes in membrane structure are probably not related to any decrease in membrane permeability during the early phases of imbibition. [ABSTRACT FROM AUTHOR]

The leakage of electrolytes and the localization of chloride within the cells of of NaCl-imbibed seeds indicates the plasmalemma is quite permeable during the early stages of imbibition. However, lanthanum is not able to penetrate the plasmalemma, suggesting that the plasmalemma is not entirely porous. Freeze-fracture microscopy indicates that the plasmalemma is highly convoluted but reveals a fairly normal fracture plane. These observations suggest the membrane is a bilayer and leakiness may be more related to the degree of order within the bilayered membrane than to a primary restructuring and/or reorganization of the membrane components in the dry state. [ABSTRACT FROM AUTHOR]