Transport of Inorganic Ions in Tonoplast Vesicles
Since the tonoplast proton pumps create a positive membrane potential in the vacuole, the maintainance of high cytoplasmic K+ and the accumulation of Cl− and NO3 − in the vacuole requires only passive transport mechanisms (channels or uniports) for these ions, energized by ∆Ψ. On the other hand, the vacuolar accumulation of Na+ and Ca2+, and the retrieval of stored nutrient anions such as NO3 − for metabolic use requires active transport mechanisms, which we now believe to be energized by proton efflux from the vacuole. This paper will discuss our work on these proton-coupled secondary transport mechanisms, with emphasis on their physiological significance, the technical problems involved, and the many questions remaining to be investigated.
KeywordsAcridine Orange Proton Leak Passive Permeability Active Transport Mechanism Tonoplast Vesicle
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