RESPIRATION AND GROWTH OF TOMATO FRUIT

The respiration rate and diameter expansion growth of young tomato fru it were measured simultaneously and related to changes in carbon impor t and plant water status, Respiration rate was directly proportional t o the volume expansion rate of fruit growing on isolated plant tops at a positive water potential, whether the growth rate was changed by ch anging the fruit temperature or by manipulating the source:sink ratio of the plants, From the latter relationship, the maintenance respirati on rate was estimated by extrapolation to zero growth and was found to be about 25% of the respiration rate of the average fruit at 21 degre es C, Alternatively, when carbon import was prevented by heat-ringing the fruit peduncle, the respiration rate of the fruit declined to abou t 40% of the control rate and remained steady, while the expansion rat e then declined steadily to <10% of the control rate, These results sh ow that fruit expansion was not contributing significantly to fruit re spiration, Indeed, large fluctuations in fruit expansion rate could al so be induced by repeated darkening and illumination of potted plants without a corresponding change in fruit respiration, Most significantl y, fruit expansion was considerably reduced when plants were allowed t o wilt, but there was no change in fruit respiration rate unless the f ruit peduncle was subsequently heat-ringed, We conclude that a major p art of the respiration of young tomato fruit was determined by the rat e of carbon import, or associated processes, and that fruit expansion per se can occur with relatively low respiratory costs,