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Succinoxidase Activity of Avocado Fruit Mitochondria in Relation to Temperature and Chilling Injury throughout the Climacteric Cycle ¹

^a Department of Plant Sciences, University of California, Riverside, California 92521

Mitochondria were isolated from `Fuerte' avocado fruit (Persea americana Mill.) at four different stages of the respiratory climacteric. Preclimacteric fruit had the highest rate of succinate oxidation and the postclimacteric mitochondria the lowest. Subsequently, successive additions of ADP increased the respiratory control ratio.

Arrhenius plots of succinate oxidation of intact mitochondria from climacteric rise and climacteric peak fruit showed two transition temperatures, while only one was observed in preclimacteric fruit. The low temperature phase transition was at about 9 C, while the high one was at 20 C. In postclimacteric fruit, the low temperature transition decreased to between 5 and 2 C. The state 3 rate of succinate oxidation was highest for mitochondria from preclimacteric fruit and decreased for each later stage. The state 4 rates for preclimacteric and climacteric rise were the same, while both the climacteric peak and postclimacteric rates were about 40% lower than the preclimacteric O₂ uptake.

The results indicate continuous changes in the mitochondrial membrane of the electron transport chain throughout the climacteric cycle. The change in the membrane influencing the phosphorylation system is greatest between climacteric rise and peak stages. Mitochondrial membranes of postclimacteric fruit are presumed to change from flexible disordered to solid ordered phase at a lower temperature than those of other climacteric stages.

¹ This research was supported in part by the Rockefeller Foundation.