Translocation of 14Carbon in Tobacco following Assimilation of 14Carbon Dioxide by a Single Leaf

¹⁴CO₂ was assimilated by single leaves (presentation leaves)of tobacco plants for periods of 2–3 hours. The plantswere then kept in air in continuous light and the redistributionof radioactivity determined at various times up to 96 hours.There was a complete turnover of sucrose in the presentationleaf in about 24 hours without change in amount. Starch turnedover more slowly and simultaneously increased in amount. 20–30per cent. of the radioactivity appeared to be irreversibly incorporatedinto the presentation leaf. Of the material exported from thepresentation leaf some 3 per cent. reached the upper leavesand stem apex. Import into leaves above the presentation leafwas completed in about 6 hours. No activity appeared in leavesbelow the presentation leaf, therefore the balance of the exportedactivity was retained in the stem and roots. The distribution of radioactivity in the leaves followed a well-definedpattern determined by the vascular interconnexions. Radioautographs of stem sections provided some information concerningdistribution of radioactivity in the stem.