ETHYLENE EVOLUTION AND AMMONIUM ACCUMULATION BY NUTRIENT-STRESSED TOMATOES GROWN WITH INHIBITORS OF ETHYLENE SYNTHESIS OR ACTION

Ammonium accumulation and ethylene biosynthesis by plants may be interrelated events that lead to expression of symptoms of environmental stress. Compared to unstressed tissues, foliage of environmentally stressed plants often has accelerated rates of ethylene evolution and enhanced accumulation of uncombined ammonium. The present study assessed the effects of inhibitors of ethylene synthesis or action on ethylene evolution, ammonium accumulation, and symptoms of tomato (Lycopersicon esculentum Mill.) stressed by ammonium toxicity or nutrient (P, K, Ca, Mg) deficiency. 'Heinz 1350' and neglecta-1 tomato were grown in sand culture in greenhouses. Plants receiving ammonium nutrition and (aminooxy)acetic acid (AOA), a purported inhibitor of ethylene synthesis, had no symptoms of ammonium toxicity. Ethylene evolution and ammonium accumulation were suppressed by AOA. Silver thiosulfate (STS), a purported inhibitor of ethylene action, delayed the appearance of ammonium toxicity symptoms and maximum ethylene evolution, but had no effect on maximum ammonium accumulation relative to the plants treated without STS. Ammonium accumulation and ethylene evolution by nutrient-deficient plants, especially Ca and Mg, were inhibited by AOA. AOA delayed expression of symptoms of nutrient deficiency for several days and elevated elemental concentrations but restricted growth of nutrient-deficient plants. The results of this study suggest that ammonium accumulation and ethylene biosynthesis are common intermediates in development of symptoms in nutrient-stressed plants.