Symbiosis of Astragalus cicer with its microsymbionts: partial nodC gene sequence, host plant specificity, and root nodule structure

Astragalus cicer (cicer milkvetch) nodule bacteria were investigated for ho st plant specificity and partial nodC gene sequences, whilst their native h ost was studied for the microscopic structure of root nodules. The strains under investigation formed nodules not only on the original host but also o n Astragalus glycyphyllos, Astragalus sinicus, Lotus corniculatus, and Phas eolus vulgaris. The nodules induced on the cicer milkvetch were classified as indeterminate and characterized by apical, persistent meristem, a large bacteroid region with infected and uninfected cells, and elongated bacteroi ds singly located inside peribacteroid membranes. By comparison of the part ial nodC gene sequences of a representative strain of astragali rhizobia to those contained in the GenBank database, a close symbiotic relationship of A. cicer microsymbionts to Rhizobium sp. (Oxytropis) was found.