RESPIRATORY ACTIVITY AND DURATION OF LIFE OF APPLES GATHERED AT DIFFERENT STAGES OF DEVELOPMENT AND SUBSEQUENTLY MAINTAINED AT A CONSTANT TEMPERATURE

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Abstract
The respiratory activity at normal temps. of Bramley''s Seedling apples gathered at various stages of growth has been examined and recorded. There is a marked fall in respiratory activity per unit fresh wt. during the early stages of the development on the tree[long dash] the period of cell division. The fall continues, but much more slowly, during the main growth period[long dash]the period of cell enlargement. The respiratory activity per unit N, and probably also per unit protein, remains approx. constant during the main period of growth by cell-enlargement. During the early stages of growth by cell-division the respiratory activity per unit N is somewhat higher. It is suggested that respiratory activity on the tree is not limited by the effective amt. of enzyme present, but remains constant as a result of an auto-regulation of substrate conc., through a linkage between respiratory activity, formation of new cytoplasm, uptake of water and increasing size of cell. During both growth periods the respiratory activity falls after gathering, both per unit fresh wt. and per unit N. The drift in respiratory activity per unit fresh wt. after gathering shows, in general, 4 main phases. These are discussed in relation to their causation. Particular attention has been devoted to the 3d or climacteric phase, and to the effect of temp., O2 supply and ethylene upon its onset. The climacteric rise in respiratory activity, first described in part I of this series, has been shown to occur in fruit on the tree as well as in fruit gathered at any stage of maturity. Evidence is produced and discussed which indicates that the climacteric occurs as a result of the production of ethylene by the fruit and of an autostimulation produced by this gas when present in the tissues in amts. above critical threshold values.