Ripening and in Vitro Retention of Respiratory Control by Avocado and Pear Mitochondria

The retention of respiratory control ("survival") by mitochondria held at 25 C was studied in relation to the ripening of two varieties of avocado (Persea americana Mill. var. ;Fuerte' and ;Hass') and one variety of pear (Pyrus communis. L. var. ;Bartlett') fruit. The survival of avocado mitochondria increased from 8 to 10 hours when isolated from unripe, preclimacteric fruit, to 48 hours when isolated from fully ripe, postclimacteric fruits. Although rates of alpha-ketoglutarate oxidation, respiratory control, and ADP/O decreased somewhat in the postclimacteric phase, survival per se was not affected. Pear mitochondria survived for more than 30 hours regardless of the physiological age of the source.Exposure of postclimacteric avocado mitochondria to a preclimacteric supernatant fraction curtailed their survival. The harmful effect of some unknown substance(s) in the preclimacteric avocado supernatant fraction was confirmed by utilizing pear mitochondria as an independent test system.