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SUMMARY Direct sampling of volatiles emanating from pears is shown to be a potentially useful and non‐destructive means of assessing fruit ripeness as it is affected by time or treatment such as exposure to ionizing radiation.

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.

Maceration at liquid nitrogen temperatures, use of polyvinylpyrrolidone, and careful pH control are essential to the isolation of ribosomes and polysomes from deciduous fruit tissue. Characteristics of the ribosomes and constituent RNA are described. Superimposed intracellular radiation injury stimulates the synthesis of new ribosomes and underscores a major transition in the dynamics of the ribosomal system coincident with the climacteric rise.Fruits and leaves have often been used as sources of tissue committed to senescence and death. In particular, intracellular events in ripening avocado (2), apple (11), and pear (8)

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