Export of organic materials from developing fruits of pea and its possible relation to apical senescence

In the G2 line of peas (Pisum sativum L.) senescence and death of the apical bud occurs only in long days (LD) in the presence of fruits. Removal of the fruits prevents apical senescence. One possible reason for the senescence-inducing effect of fruit is that the fruits produce a senescence-inducing factor which moves to the apical bud and is responsible for the effect. For this to be possible there must be a transport mechanism by which material may move from the pods to the apex. To examine the extent of fruit export, pods were labeled via photoassimilation of (14)CO(2) beginning 12 days after anthesis. Under LD conditions, 1.14% of label fixed was transported from the pods with only 10.5% of this found in the apical bud and youngest leaves after 48 hours, the remainder being found principally in other developing fruits and mature leaves. During the onset of apical senescence, less total label was actually exported to the apical bud than at other times. In addition, more total export occurred from pods in short days than in LD, with the apical bud receiving a greater percentage than in LD. Thus the amount and distribution of export would not seem to support the idea of specific export of targeted senescence-promoting compounds. Girdling of the fruit peduncle did not change the characteristics of export suggesting movement via an apoplastic xylem pathway.