[Translocation of (14)C-labelled assimilates in the phloem of Pelargonium zonale and Phaseolus vulgaris]

Abstract

After the laminae of leaves of intact plants had been exposed to (14)CO2 the translocation of (14)C-labelled assimilates across the petioles starts very quickly: 6 to 10 min later (14)C-activity could be detected in the basal part of the petioles. The way of distribution within the plant seems to be influenced mainly by the age of the (14)CO2-assimilating leaf, however, but not in the sense of an unidirectional movement; little but distinct amounts of (14)C were carried also from younger yet full expanded leaves down to older leaves, within 20 min (in Phaseolus) or 180 min (in Pelargonium). Besides sucrose, which was shown by paper chromatography to be the main form of assimilates translocated in these species, we identified sugar phosphates, hexoses, and some organic acids in the petiole and stem tissue as being radioactive also. In our experiments, the petiole segments did not contain any remarkable amount of (14)C-labelled starch.