SPACES,BARRIERS, AND ION CARRIERS: ION ABSORPTION BY PLANTS

Epstein , Emanuel . (U. California, Davis.) Spaces, barriers, and ion carriers: ion absorption by plants. Amer. Jour. Bot. 47(5) : 393—399. 1960.—Ions from the external medium initially invade “outer” or “free” spaces of plant cells and tissues, by diffusion and ion exchange. This process is essentially non-metabolic and non-selective, and is readily reversible. The spaces accessible in this manner seem to be confined to the cell walls. From here, ions are selectively transported into “inner” spaces separated from the “outer” space by diffusion barriers. Ion carriers accomplish the selective transfer of the ions across the barriers or membranes, first into the cytoplasm and thence into the vacuole. The second step, into the vacuole, can be by-passed by those ions moving into the xylem elements and up to the shoot, and some transport to the shoot may skirt the active transport mechanisms entirely.