EN
The ontogeny and (ultra)structure of vascular tissue in Lupinus luteus L. root nodules were studied by light and transmission electron microscopy in juvenile nodule primordia up to the 11th day after inoculation. Vascular meristem originated from centripetally dedifferentiated root cortical parenchyma, endodermis and pericycle. The vascular trace was formed between bacteroid tissue initials and the root stele. In the trace's proximal part, cambial strands connecting the vascular trace and root cambium were formed. In the distal part, non-anastomosing vascular bundles started differentiating from the trace at the end of the juvenile stage. In lupine, the formative stage of the indeterminate root nodule vascular system was shown to be unique within the legumes.