Photosynthesis & respiration in developing fruits . II. Comparative rates at various stages of development

Abstract

Photosynthetic activity in green lemon and orange fruit (per unit of surface) decreased with increasing size, while green avocado fruit showed little change with changes in size. Respiration in the lemon and orange dropped rapidly during early growth causing an increase in the photosynthesis/respiration ratio as the size increased. Avocado showed little change in this ratio with fruit size. In most cases the photosynthetic rate did not exceed the compensation point in orange, lemon, avocado or cucumber fruit. It was concluded that the contribution of photosynthesis within a fruit towards its own development is small. Photosynthetic and respiratory rates of cucumber fruits were found to decrease after the phloem connecting the fruit was severed, or after the plant was defoliated, or after complete detachment from the vine. This is in contrast to a report by Kursanov (Planta 22: 240. 1934) who found greatly increased photosynthetic rates after such treatments. Orange fruits also showed a decrease in photosynthesis when the phloem was cut. These changes in respiration and photosynthesis resulting from fruit detachment were not abrupt but took place slowly over a period of several hours.