Studies in the Nitrogen Metabolism of Apple Fruits

A close parallelism in the drift of the rate of respiration and the protein-N/ non-protein-N ratio is shown to occur both in apple fruits attached to the tree and when detached from the tree at various stages of development and stored for several months at 12° C. In detached fruits the fall in respiration which occurs immediately (during the first 48 hours) after picking is only accompanied by a concomitant fall in net protein in very young fruits in which active cell division is taking place. Subsequently, in fruit of all ages when a climacteric rise in respiration occurs it is accompanied by a net increase in protein. It is argued that the climacteric rise in respiration is a result of increase in the level of protein which will be expected to reduce the ATP/ADP ratio. Over the climacteric period, although rate of respiration and net protein content both rise, R rises more rapidly than protein and, subsequently, falls at a faster rate than P. It is suggested that this may be due to the ‘new’ protein containing a higher proportion of enzyme(s) directly involved in respiration and leading, for example, to a reduction in the ATP/ADP ratio.