Pathways of ¹⁴C-Photosynthates in Main Stem and Fruit of Cucumber

Abstract

Pathways of ¹⁴C-photosythates from the 7th leaf on the 7th node of the main stem to the internodes above and below the 7th leaf, and to the fruit on the 7th node were investigated with radiocarbon.
The internodes were sampled 20 and 90min, and 20h after the beginning of ¹⁴CO₂ feeding, for 10 and 60min, respectively. Twenty min after the beginning of ¹⁴CO₂ feeding, ¹⁴C-activity was detected only in the 6th internode just below the 7th leaf, and, moreover, only in the vascular bundle connected directly to the 7th leaf. After 90min and 20h, however, ¹⁴C-activity was detected in all of the internodes observed, but was still highest in the 6th internode. In all internodes, ¹⁴C-activity as % of that in the 6th internode increased with time after ¹⁴CO₂ feeding, although the increase was somewhat delayed in the intermodes above the 7th leaf.
The fruit were harvested 2, 4 and 20h after the beginning of ¹⁴CO₂ feedingto the 7th leaf. After 2h, ¹⁴C-activity was found high only in the vascular bundle(s) situated on the 7th leaf side in the receptacle, septum, fruit axis and placenta. Moreover, 2h after ¹⁴CO₂ feeding, ¹⁴C-activity in the vascular bundle with the highest value in each fruit part was highest in the receptacle, followed by the septum and fruit axis, and lowest in the placenta. At a later time after ¹⁴CO₂ feeding, however, they showed gradually higher values which became comparable to that of the receptacle.