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

Patterns of ¹⁴C-photosynthate translocation in bean (Phaseolusvulgaris L.) seedlings have been investigated in relation tovascular-bundle continuity between exporting and importing organsby use of radioassay and tissue-clearing techniques. Assimilatefrom the primary leaves reaches the first trifoliate leaf byan indirect route. There is no direct vascular connection betweenthe primary leaves and distal tissues. Bundles of the primaryleaf petiole connect with an anastomosis at the node, and allbundles which originate from this structure descend the stem.Assimilate from primary leaves moves down the stem, and is thentransferred to an ascending pathway, the bundles of which traversethe anastomosis at the second node. The lateral leaflets ofthe first trifoliate leaf are served differentially by primaryleaves with respect to assimilate supply. Differences are relatedto position, and may be accounted for by differences in vascularcontinuity.