Transport of 14C-Assimilates in Seedlings of Phaseolus vulgaris L. in Relation to Vascular Anatomy

Patterns of 14C-photosynthate translocation in bean (Phaseolus vulgaris L.) seedlings have been investigated in relation to vascular-bundle continuity between exporting and importing organs by use of radioassay and tissue-clearing techniques. Assimilate from the primary leaves reaches the first trifoliate leaf by an indirect route. There is no direct vascular connection between the primary leaves and distal tissues. Bundles of the primary leaf petiole connect with an anastomosis at the node, and all bundles which originate from this structure descend the stem. Assimilate from primary leaves moves down the stem, and is then transferred to an ascending pathway, the bundles of which traverse the anastomosis at the second node. The lateral leaflets of the first trifoliate leaf are served differentially by primary leaves with respect to assimilate supply. Differences are related to position, and may be accounted for by differences in vascular continuity.