The translocation of photosynthetically assimilated 14C in corn

Abstract

A detailed study was made of translocation of photosynthetically assimilated 14C in 3- to 6-week-old corn plants. Corn assimilated 14C via malate and aspartate, and incorporated most of the 14C into sucrose, the only translocation compound. Lowering the temperature from 26° to 8 °C delayed the incorporation of 14C into sucrose, but had no effect on the distribution of 14C among the intermediates. Recent 14C assimilate was translocated very rapidly from the fed area, the amount remaining in the fed area decreasing logarithmically with time. The translocate moved down the vascular bundle it entered in the fed area, with no detectable lateral movement. The logarithmic profile in the leaf blade appeared to be the result of a temporary accumulation of the labelled pulse in the separate vascular bundles. This accumulation of sucrose in the veins could be eliminated by cutting out the fed area. Between 80 and 90% of the assimilated 14C was translocated from the fed area of the leaf in 24 hours with 50% moved out in the first 30 minutes. Both the rate of translocation and the total amount moved out of the fed area increased as the temperature was changed over the range 7 to 26 °C. Each leaf of young corn plants both imported assimilates from and exported assimilates to all other parts of the plant.