Wash-Activated Na+/H+ Exchange in Tonoplast Vesicles from Beta Vulgaris Storage Root Disks
The presence of a large central vacuole in higher plant cells enables the accumulation and storage of osmotica which would otherwise interfere with cytoplasmic processes. Such compartmentation is especially necessary in the case of Na+, which at the concentrations often found in the vacuole is a general inhibitor of protein synthesis (Wyn Jones et al., 1979). By implication, then, it might be expected that those plants utilizing Na+ as an osmoticum (particularly halophytes) are capable of energy-dependent Na+ transport across the tonoplast. This expectation has been confirmed by Blumwald and Poole (1985), who have recently demonstrated Na+/H+ antiport in tonoplast vesicles from red beet (Beta vulgaris L.). The prevailing pH gradient across the tonoplast (ΔpH = 2 units) would therefore be capable of energizing a vacuolar/cytoplasmic Na+ concentration ratio of 100-fold for the minimum expected H+/Na+ stoichiometry of 1.
KeywordsFluorescence Quenching Acridine Orange Storage Tissue Fluorescence Recovery High Plant Cell
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