INHIBITION OR PROMOTION OF TOMATO FRUIT RIPENING BY ACETALDEHYDE AND ETHANOL IS CONCENTRATION-DEPENDENT AND VARIES WITH INITIAL FRUIT MATURITY

'Castlemart' tomato (Lycopersicon esculentum Mill.) pericarp discs wer e used to study the physiological effects of acetaldehyde and ethanol on fruit ripening. Short-term exposure of discs from mature-green frui t to acetaldehyde vapors on a fresh mass basis (less than or equal to 500 mu g.g(-1)) or ethanol vapors (less than or equal to 3 mg.g(-1)) p romoted ripening, while higher concentrations inhibited ripening. Disc s from mature-green fruit absorbed greater amounts of ethanol and prod uced significantly higher concentrations of acetaldehyde than discs fr om breaker fruit. Ripening was promoted by ethanol when tile discs mer e unable to retain or produce a certain level of acetaldehyde. Inhibit ion of ripening by 4 hours of exposure to ethanol (6 mg.g(-1)) was alm ost completely abolished by hypobaric treatments (18 kPa for 24 hours) . However, acetaldehyde-induced ripening inhibition (2 days exposure t o 180 mu g.g(-1)) was only slightly reduced by vacuum. Concentrations of acetaldehyde and ethanol that inhibited ripening reduced C2H4 produ ction, whereas lower concentrations of acetaldehyde and ethanol that p romoted ripening increased C2H4 production. Application of 4-methylpyr azole, an alcohol dehydrogenase inhibitor, enhanced acetaldehyde-induc ed ripening inhibition and reduced ethanol-induced ripening inhibition or promotion at all concentrations of acetaldehyde and ethanol tested . The inhibition of promotion of ripening of excised tomato pericarp d iscs by ethanol and acetaldehyde depended on initial fruit maturity, a pplied volatile concentration, and duration of exposure.