Tubulin Cytoskeleton Organization in Cells of Determinate Nodules in Vigna radiata, Vigna unguiculata, and Lotus corniculatus

Tubulin cytoskeleton rearrangements play an important role in the cell differentiation of symbiotic nodules in legumes. However, the organization of the tubulin cytoskeleton has been investigated only for four legume species forming determinate nodules (with limited nodule meristem activity). In this study, microtubule organization was studied in three species (Vigna radiata, V. unguiculata, and Lotus corniculatus) with determinate nodules using confocal laser scanning microscopy and quantitative analyses. Histological organization in young nodules of V. radiata and V. unguiculata resembled the recently reported zonation in young nodules of Glycine max. In addition, bacteroids in nodules of these species were significantly enlarged compared to free-living bacteria. Organization of endoplasmic and cortical microtubules in young infected cells and uninfected cells and that of cortical microtubules in nitrogen-fixing cells demonstrated general patterns for determinate nodules, whereas endoplasmic microtubules in nitrogen-fixing cells showed species-specific patterns. Thus, the presence of both general and species-specific patterns of tubulin cytoskeleton organization was confirmed in determinate nodules.