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

Abstract

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