Tubulin Cytoskeleton in Symbiotic Nodules of Black Medic (Medicago lupulina L.)

Medicago lupulina L. is of considerable interest for use in agriculture. However, its symbiosis with nodule bacteria remains poorly investigated. In this study, a detailed analysis of the morphology of bacteroids in black medic nodules was conducted, which revealed certain differences from the morphology of bacteroids in the nodules of related species M. sativa and M. truncatula. A detailed analysis of the organization of the tubulin cytoskeleton in M. lupulina nodules revealed a regular pattern of cortical microtubules in meristematic and infected cells, while an irregular pattern was observed in uninfected and colonized cells. Endoplasmic microtubules were associated with infection threads and droplets. This organization of the tubulin cytoskeleton is characteristic of M. truncatula. At the same time, unlike the nodules of M. truncatula, the endoplasmic microtubules in infected cells in nitrogen fixation zone rather than a regular pattern (radial orientation) formed an intermediate one (mainly oriented irregularly, but to some extent radially). Thus, intrageneric variability in the organization of the tubulin cytoskeleton was discovered for the first time.