THE EFFECTS OF FLOWERING AND FRUIT FORMATION ON THE SUPPLY OF PHOTOSYNTHETIC ASSIMILATES TO THE NODULES OF <i>PISUM SATIVUM</i> L. IN RELATION TO THE FIXATION OF NITROGEN

Abstract

SUMMARY Both nitrogenase activity and the accumulation of 14 C‐labelled photosynthates in the nodules of pea plants in nitrogen‐free culture reached maxima shortly before flowering and fruit development. During the period from flowering to fruiting, nitrogenase activity and accumulation of 14 C‐photosynthates in the nodules declined by 60%, whereas the photosynthesis of the plant doubled. Studies of the translocation of the photosynthates within the plant during this period suggested that this might be due to an increase from 17% to 50% of the photosynthates which accumulated at the shoot apex. Consistent increases in nitrogenase activity over the 24 hours following removal of the shoot apex were only achieved in fruiting plants, however, although vegetative, flowering and fruiting plants all showed increased accumulation of photosynthates in the nodules. Continuous removal of flowers as they were formed over a 2‐week period resulted in a large increase in accumulation of photosynthates in the nodules and in nitrogenase activity. Other factors which may regulate nitrogenase activity in these plants are discussed.