Microautoradiographic studies of phloem loading and transport in the leaf of Zea mays L.

摘要: Microautoradiographs showed that [14C]sucrose taken up in the xylem of small and intermediate (longitudinal) vascular bundles Zea mays leaf strips was quickly accumulated by parenchyma cells abutting vessels. The first sieve tubes to exhibit 14C-labeling during experiments were thick-walled contiguous more heavily labeled cells. (These two cell types typically have numerous plasmodesmatal connections.) With increasing feeding periods, greater proportions thick- thin-walled became labeled, but few associated with companion (Only are cells.) When portions exposed 14CO2 for 5 min, cells-regardless their location relation vessels or tubes-were most consistently bundles, label (14C-photosynthate) appeared a proportion than tubes. After 5-min chase 12CO2, any other type leaf. 10-min even labeled. generally less Although all fed min given 12CO2 chase, only five 72 below 14CO2-exposed contained Moreover, thick-walledsieve “transport region” always abutted 14C-labeled results this study indicate (1) able retrieve at least sucrose from transfer it tubes, (2) not involved long-distance transport, (3) capable themselves accumulating photosynthates apoplast, without serving as intermediary