The extraction of photosynthate high in [11C]sucrose and its translocation in sunflower stems

Abstract

A technique was developed to biosynthesize a water-soluble extract of 11C-labeled photosynthate high in [11C]sucrose. The extract can be produced in less than 1 half-life (20 min) and is of high activity. When 11C-labeled extract was fed to the individual vascular bundles of other living plants, 11C was taken up and translocated, and on the basis of direct and indirect evidence it was largely in the form of [11C]sucrose. 11C-labeled extract, if fed to a flap or gentle scraping on the surface of a sunflower stem (or corn, cow-parsnip, pine or elm), was translocated both apically and basally from the feed point. Incisions into xylem vessels produced very rapid tracer movements which seemed to be associated with xylem vessel liquid cavitation and also transpiration pull. Shallower cuts produced translocation patterns similar to 11CO2 leaf feedings and are thought to be largely in the phloem. Phloem transport was blocked by ice chilling; xylem transport was only slightly affected by ice, if at all. Phloem translocation profiles often displayed steps at the front of mass flow, and later appeared to have peaks of activity moving along them. The movements were sometimes rapid (> 6 cm min-1) and appeared to be complex, as if different channels were conducting them at different speeds in parallel.