Comparison of upward and downward translocation of C from a single leaf of sunflower

When single leaves attached at a given node were allowed to carry on photosynthesis in ¹⁴CO₂ for 30 min, younger plants showed a higher proportion of upward translocation than did older plants. Downward translocation of ¹⁴C-photosynthate was stimulated by ATP pre-treatment of the translocating leaf, while upward translocation was not affected by ATP. A similar phenomenon was observed in the translocation of ¹⁴C-sucrose infiltrated into a leaf with or without ATP. Downward translocation of photosynthate was inhibited by DNP pre-treatment of a fed leaf. Upward translocation, however, was not affected by DNP. Thirty min after infiltration of ¹⁴C-glucose into a leaf, almost all the ¹⁴C translocated upwards was found to be in the form of glucose, while a great part of the ¹⁴C translocated downwards was in the form of sucrose. In the case of translocation of infiltrated ¹⁴C-sucrose, ¹⁴C found both above and below the fed leaf was mainly in the form of sucrose.