It is generally accepted that the climacteric phase of ripening fruits is well suited for the study of cellular senescence (1). Since a surge in respiratory activity is the dominant, readily measurable phenomenon, mitochondria are implicated as the sites of causal events. This view was embodied in the early work of Millerd et al. (19) with the resulting postulate that uncoupling of oxidative phosphorylation permitted an increased respiratory rate. Along similar lines, Hulme (7) and Pearson and Robertson (21) attributed the rise in respiration to the availability of phosphate acceptor (ADP) resulting from increased protein synthesis and accelerated demands for energy. However, with specific reference to mitochondrial protein, data on the yield of particulate protein (27) and on the incorporation of amino acids into mitochondrial protein (28) indicate a decline in synthetic activities as fruit reach the climacteric peak.Richmond and Biale (23), Sacher (37), and especially Young and Biale (44) have questioned the prevalence of "uncoupling" or "ADP control" in ripening fruit cells. Moreover, the work of Lance et al. (10), Hulme et al. (8,9) and the experiments reported below, reveal that mitochondria remain functionally sound and "cotipled" throughout the climacteric phase.

T'b is comilitmication emphasizes the nieed for conltin1uouts conitrol of pH when macerating acidic plant tissues for the l)url)ose of isolating tightly coupled mitochondria. A useful device for such control is described.Mitochonidria capable of oxidative but not pl)osphorylative activity have been isolated fromli apple fruits wlhenl either alkaline homogeniates (5) or l)oIyvinylpyrrolidone (PV7P) (1) was used to supl)ress phenolic compounds. However, it was niot until a pH slightly below 7, pluis 0.5 % I'VP, wvere used that phospliorylating, "coupled" miitoclhonldria were obtained froml the l)arenchymatous tissues of both pear andl apple fruits (7,8). Loomlis and Battaile (6) have sinice slioNvni that PVP is less effective at an ailkalinie pH. Wiskich (9) utilized an isolation medium at pH 7.4, btut containing 1 % PVP, to obtain apple mitochondria with respiratory colntrol ratios (RCR) of somewhat less than 2. Hulmle ct al. (2) reported results similar to those obtainied by Wiskiclh.

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