Effects of organic amines on α-aminoisobutyric acid uptake into the vacuole and on ethylene production by tomato pericarp slices

Experiments were conducted to test the possibility that organic amines inhibit ethylene production by inhibiting transport of the ethylene precursor, 1-aminocyclopro-pane-1-carboxylic acid (ACC), into the vacuole. α-Aminoisobutyric acid (αAIB) was used as a model substrate to study ACC uptake into the vacuole in relationship to ethylene production in pericarp slices of Lycopersicon esculentum Mill. cv. Liberty treated with and without organic amines and related substances. Organic amines (polyamines and other basic amines) inhibited αAIB uptake into the vacuole. These amines also enhanced ACC accumulation in the tissue and reduced the passive efflux of αAIB from the vacuole. Overall, ethylene production was inhibited. The inhibition of αAIB transport and of ethylene production followed a polyvalent cationic progression in the order polyamines > diamines> basic 1-amino acids. Ca²⁺, but not Mg²⁺, strongly stimulated αAIB uptake into the vacuole and ethylene production. At equal concentrations, Ca²⁺ counteracted the inhibitory effects of polyamines on both αAIB uptake and ethylene production. Competitive and irreversible inhibitors of polyamine biosynthesis stimulated αAIB uptake into the vacuole and ethylene production. The results indicate an apparent relationship between polyamines, ACC uptake into the vacuole and ethylene production.