NITROUS-OXIDE INHIBITION OF ETHYLENE PRODUCTION IN RIPENING AND SENESCING CLIMACTERIC FRUITS

The anti-ethylene effects of nitrous oxide have been demonstrated for the first time in the ripening and senescence sequences in tomato and avocado fruit. Continuous gas treatment by 80% nitrous oxide plus 20% oxygen had striking inhibitory effects on ethylene production in the two fruit species, though ethylene biosynthesis levels differed greatly. In preclimacteric treated fruits, nitrous oxide largely extended the lag period, and additively lowered ethylene production rate in tomatoes. In fruits treated at the climacteric stage, nitrous oxide markedly inhibited autocatalytic ethylene evolution. In fruit pretreated with exogenous ethylene, nitrous oxide also reversed induced autocatalysis as an antagonist of ethylene action. At a later stage, some fruits in air exhibited a second ethylene rise as a signal of ultimate senescence. This was characterised by coincidence of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity peak, elevated ACC levels and ACC synthase activity. Nitrous oxide blocked or delayed this senescence ethylene upsurge. Analysis of the metabolic processes involved in the various counteracting actions of nitrous oxide revealed a very significant ethylene antagonist role of the gas which, unlike carbon dioxide, was non-toxic.