Transport and Compartmentation of 1-Aminocyclopropane-1-Carboxylic Acid and Its Structural Analog, alpha-Aminoisobutyric Acid, in Tomato Pericarp Slices.

The uptakes of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor to ethylene, and its structural analog, alpha-aminoisobutyric acid (alphaAIB) by tomato pericarp slices were investigated. Both uptakes show a biphasic (saturable-linear) dependence on external concentration of the transported amino acid. At low concentrations, ACC uptake is competitively inhibited by alphaAIB and vice versa. Both uptakes also are inhibited by other neutral amino acids but not by acidic or basic amino acids. ACC and alphaAIB uptakes are metabolically dependent and are increased with time of tissue incubation. alphaAIB efflux patterns from pericarp slices indicated three distinct alphaAIB compartments having efflux kinetics consistent with those for cell wall, cytoplasm, and vacuole. The bulk of the alphaAIB taken up by pericarp tissue is sequestered into the vacuole. The ability of pericarp tissue to accumulate alphaAIB in the vacuole declines with fruit development.