Effect of the cationic chelator EDTA on the ripening of normal tomato fruit and the non-ripening mutants nor, rin and Nr

Abstract

Tomato (Lycopersicon esculentum Mill.) plants cv. Rutgers and lines containing the mutants nor, rin and Nr in a nearly isogenic background were grown in a sand culture in a greenhouse. Fruit on the mutant lines ripened much more slowly than those on the wild-type plants, especially those containing the nor and rin characters. Ripening progress was assessed by measuring increasing total surface reflectance, softening, CO<inf>2</inf> output, and ACC and ethylene production at defined stages during the development of wild-type fruit and at physiologically equivalent stages for the mutants. Fruit from the nor and rin lines showed none of the characteristic changes associated with normal ripening except a slight rise in ACC in 'over-ripe' nor fruit and in ethylene in 'mature' nor and rin fruit. Nr fruit showed characteristic ripening changes at about half the rate of wild-type fruit, but much higher ACC and slightly higher ethylene levels were found. EDTA (1 g/l) was added to the nutrient solution and alterations to the ripening patterns of the four lines were observed. No significant changes were induced in wild-type or Nr except that in the latter line, ethylene evolution was cut by about 30% during ripening. However, nor and rin fruit were induced to colour to an extent not far from that of the ripe wild-type. The rin fruit began to soften; CO<inf>2</inf>, ACC and ethylene evolution was stimulated. Although only some of the characteristics of the climacteric pattern of ripening have been restored to nor and rin lines, it is suggested that these results strengthen the link between the chelation of divalent cations such as calcium and the induction of the climacteric pattern of ripening in fruit. © 1992.