Salt-induced Pinocytosis in Barley and Bean

The ultrastructure of the halophyte, Salicornia europea L. wascompared with barley and bean plants grown under saline conditions.S. europea exhibited frequent pinocytotic vesiculation in thehypocotyl and stem but less vesiculation in the root and cotyledon.No vesiculation was observed in barley and bean plants grownin the absence of sodium chloride though plants grown in thepresence of sodium chloride demonstrated vesiculation, morein barley than in bean. Both the halophyte and the glycophytesdemonstrated more pinocytosis in the plant tops than in theroot system. The multivesiculate structures observed were connectedto the wall free space at the early stages of their formationand have not been reported in plants under normal physiologicalconditions. The observations on pinocytosis are discussed in relation totoxic ion compartmentation and salt resistance in plants.     

Extrusion of Sodium Ions by Barley Roots: II. Localization of the Extrusion Mechanism and its Relation to Long-distance Sodium Ion Transport

An active sodium effux hasbeen demonstrated in excised barleyroots. Isolated cortical and stelar tissues from the same materialdo not show any evidence of such an efflux mechanism. When intactbarley plantswere allowed to absorb ²²Na active sodium extrusionwas not observed, although the percentage of ²²Na transportedto the shoot was stimulated 20 to 40 percent by ouabain at 5x 10^–4 M. Absorption and long-distance transport of phosphatewas unaffected by ouabain at this concentration. Interpretationof these data lead to the conclusion.that the sodium-effluxpump in barley roots is located at or near the endodermis externalto the Casparian band. This pump thus provides a mechanism wherebysodium can be partially excluded from the shoots of barley plants.     

Salt Retention by Bean Hypocotyl

The ultrastructure of hypocotyl, epicotyl, and petiole of bean(Phaseolus vulgaris, L.) was investigated in plants grown ina basic solution in the absence or presence of high levels ofchloride salts. The hypocotyl tissue of both control and salt-treatedplants showed frequent vesiculation similar to that previouslyobserved in the root and hypocotyl of the halophyte, Salicorniaeuropea, L. These vesicles were not previously observed in theroot and leaf of bean plants that were grown under identicalconditions in the absence of high levels of chloride salt. Experiments concerning the localization of chloride as electron-densesilver-complex showed that the vesicles contain a chloride concentrationas high as the cytoplasmic phase or the free space. These resultsare discussed in relation to the ionic retention property ofthe bean hypecotyl and the role of vesiculation in salt resistanceof plants.     

Extrusion of Sodium Ions by Barley Roots: III. The Effect of High Salinity on Long-distance Sodium Ion Transport

The quantity of sodium transported to the shoots of intact barleyplants was stimulated by 0·5 mM ouabain when the sodiumchloride level of the bathing medium was below 100 mM. At sodiumchloride concentrations of 100 mM or more this ouabain-stimulatedsodium transport was not observed. Equiosmotic mannitol, equimolarpotassium chloride or equivalent calcium chloride solutionsdid-not affect the ouabain-stimulated sodium transport froma basic medium containing 10 mM sodium chloride. It is suggestedthat under the present experimental conditions the increasedsodium uptake by the root cells at sodium chloride concentrationsof 100 mM or more masks the extrusion process.     

Interactions in the Absorption of Monovalent Cations by Excised Radish Roots

Preferential absorption of potassium over sodium has been observedwith excised radish roots using a wide range of concentrationsin the bathing medium. This result is contrary to the situationobserved in most other plants which have been investigated,where it is found that at high external concentrations (>1·0mM) the uptake of potassium is less specific and the rate ofsodium absorption exceeds that of potassium. In radish rootscalcium does not interact with the monovalent cation absorptionin the higher range of concentration and the sodium absorptionis not sensitive to chloride-sulphate substitution. These resultsare discussed in relation to salinity-tolerance and potassium:sodiuminteractions.