The use of pretreatments for 24 h prior to storage, under anaerobic condtions, or in the presence of the natural metabolic products, acetaldehyde (AA) and ethanol, to delay fruit ripening, was found to be effective with several climacteric fruits, among them avocado, mango, peach and tomato. The delay in ripening of avocado, peach and tomato was accompanied by inhibition of ethylene production and of fruit softening. The maintenance of fruit firmness was associated with a decrease in the activities of cell-wall-degrading enzymes, including endoglucanases (Cx), polygalacturonases (PG) and b-galactosidases. In peaches the AA- and N2-treated fruits were firmer after 3 weeks storage and contained higher amount of insoluble pectin than untreated controls. We showed that AA vapors are able to inhibit ripening, ethylene production and ethylene induction in the presence of 1-amino-cyclopropane-1-carboxylic acid (ADD) in avocado and mango tissue. Ethylene induced by ACC is taken as an indicator of ACC oxidase activity. ACC oxidase activity in AA-treated avocado fruit was much lower than in the untreated fruit. In carnation flowers very little ethylene was produced by ethanol-treated flowers, and the normal increases in ACC content and ACC oxidase activity were also suppressed. Using kinetic studies and inhibitors of alcohol dehydrogenase (ADH), we showed that AA, not ethanol, was the active molecule in inhibiting ripening of tomato fruit. Application of anaerobiosis or anaerobic metabolites was effective in reduction of chilling injury (CI) in various plant tissues. Pretreatment with a low-O2 atmosphere reduced CI symptoms in avocado; this effect was associated with higher content of the free sylfhydryl (SH) group, and induction of the detoxification enzymes, catalase and peroxidase. Application of AA maintained firmer and brighter pulp tissue (non-oxidative), which was associated with higher free SH content, lower ethylene and ACC oxidase activities, and higher activities of catalase and peroxidase. Ethanol was found to reduce CI in other plant tissue. In roots of 24-h-old germinated cucumber seeds, exposure to 0.4-M ethanol shock for 4 h reduced chilling-induced ion leakage. In cucumber cotyledons it appears that alcohols may reduce CI by inducing stomata closure. In cotyledon discs held in N2 at 10C for 1 day, there accumulated sufficient endogenously synthesized ethanol to confer tolerance to chilling at 2.5C for 5 days.
Sweet Pepper (Capsicum annuum L.) Fruits Contain an Atypical Peroxisomal Catalase That Is Modulated by Reactive Oxygen and Nitrogen Species