ROLE OF REDUCED OXYGEN INTERMEDIATES IN THE ONSET OF SENESCENCE PROCESSES IN FRUIT AND STORAGE ORGANS

In tomato fruit (Lycopersicon esculentum) there was an increase in H₂O₂ and lipid peroxides at the early stages of ripening, prior to the onset of ethylene evolution. Endogenous peroxide levels in pear fruit (Pyruscommunis) were found to increase during senescence in both Bartlett and Bosc varieties. Application of glycolic acid, serving as substrates for the formation of H₂O₂, increased the peroxide content of the tissue and accelerated the onset of ripening, as measured by increased softening and ethylene evolution. Ripening processes were similarly promoted when peroxides were conserved by inhibiting the activity of catalase with hydroxylamine or potassium cyanide. By comparison, the inhibition of glycolate oxidase with alpha-hydroxy-2-pyridineme-thanesulfonic acid decreased the peroxide content of the tissue and delayed the onset of ripening.

Application of ethylene stimulated the formation of peroxides in pears. Likewise application of ethylene (10/ul/1) and propylene (500 ul/l) to potato tubers (Solanum tubersum L.) resulted in an upsurge of respiration and a concomitant rise in peroxides. When applied in 100% O₂, the effect of ethylene and propylene on respiration and peroxide formation was augmented. Ethylene (10, 100 and 1000 u1/l) in combination with different concentrations of oxygen (21, 60, and 100%) were used to initiate lycopene synthesis in detached fruits of the rin mutant in tomato (Lycopersicon esculentum Mill.). The fruit synthesized little or no lycopene in the presence of 10, 100 or 1000 ppm ethylene in air. However, lycopene synthesis was initiated in fruits kept in 60% or 100% O₂ in the presence of 10 ppm ethylene.

The results indicate that the onset of ripening processes correlate with the peroxide content in fruit tissues, as occurring normally or as influenced by the treatment.

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