Abstract
Chinese liquorice (Glycyrrhiza uralensis Fisch. ex DC.) is widely used in the food industry and as a medicine. Like other legumes, G. uralensis forms symbiotic nodules. However, the structural organization of G. uralensis nodules is poorly understood. In this study, we analyzed the histological and ultrastructural organization and dynamics of the tubulin cytoskeleton in various cells from different histological zones of indeterminate nodules formed by two strains of Mesorhizobium sp. The unusual walls of infection threads and formation of multiple symbiosomes with several swollen bacteroids were observed. A large amount of poly-β-hydroxybutyrate accumulated in the bacteroids, while the vacuoles of meristematic and uninfected cells contained drop-shaped osmiophilic inclusions. Immunolocalization of the tubulin cytoskeleton and quantitative analysis of cytoskeletal elements revealed patterns of cortical microtubules in meristematic, infected and uninfected cells, and of endoplasmic microtubules associated with infection structures, typical of indeterminate nodules. The intermediate pattern of endoplasmic microtubules in infected cells was correlated with disordered arrangement of symbiosomes. Thus, analysis of the structural organization of G. uralensis nodules revealed some ancestral features more characteristic of determinate nodules, demonstrating the evolutionary closeness of G. uralensis nodulation to more ancient members of the legume family.
Highlights
Legumes are able to form symbioses with both arbuscular mycorrhiza fungi and nodule bacteria [1]
The meristem of nitrogen-fixing nodules formed with both strains of Mesorhizobium sp. in G. uralensis was represented by small cells of irregular shape (Figure 2A–E)
We have previously suggested that the arrangement of symbiosomes in a cell is determined by a regular or irregular pattern of endoplasmic microtubules, respectively
Summary
Legumes are able to form symbioses with both arbuscular mycorrhiza fungi and nodule bacteria (rhizobia) [1]. Studying legume symbioses with rhizobia is of great interest for agriculture; the use of biological nitrogen fixation leads to a reduction in the use of mineral nitrogen fertilizers, improvements in the physical properties of the soil, increased soil biodiversity, and a beneficial effect on the environment [2,3]. Legumes are widely used in agriculture, comprising the main food crops in some areas [4]. Their particular importance is due to their high protein content; some legumes can produce phytochemicals, which are plant secondary metabolites of great interest for practical use. One such plant is Chinese liquorice (Glycyrrhiza uralensis). G. uralensis produce triterpene saponins, flavonoids and polysaccharides [5,6,7]
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