Sucrose Translocation in the Sugar Beet

Abstract

The time-course of Cl4 translocation was studied in the sugar beet, var. Klein Wanzleben, using plants pruned to a simplified source-sink translocation system. Cl4O2 was supplied to the source leaf under conditions of steady-state photosynthesis for a 7- to 10-mimite period and during the remainder of the experiment (up to 5 hours), photosynthesis continued in normal air. The time-course of accumulation of C14 in the sink was followed both by direct analysis of plants harvested at various intervals as well as by monitoring the accumulation of activity with a G-M detector positioned against the sink leaf. Although the actual rate of delivery of translocate to the sink was presumably nearly constant for the experimental period, the rate of arrival of label varied rapidly, attaining a maximal value after about 30 minutes and diminishing to near zero within an additional 50 minutes. Chromatographic analysis confirmed the rapid turn-over of label in the sucrose pool of the supply lear required by the hypothesis that sucrose is the principal source of material entering the translocate stream. In phloem-blocked leaves, it was found that superficially similar turn-over also occurred, as a result of an accelerated inversion of sucrose which displaced 614 from sucrose into terminal hexose pools.