Early stages of nodulation in roots of Oxytropis arctobia (Leguminosae) induced by the arctic rhizobial strain N31

Early stages of nodulation of roots of the arctic legume Oxytropis arctobia by the arctic rhizobial strain N31 was characterized under controlled conditions. Root hair deformation occurred as a result of inoculation of seedlings. Infection threads were seen invading target cells in the root cortex of the newly formed nodule tissue. In emergent nodules, bacteria remained surrounded by a moderately electron-dense matrix, within the intercellular space. The target cells were rich in lipid bodies, proplastids, mitochondria and polyribosomes. Fibrillar material, microfilaments and small vesicles were present at the point of bacterial release, where the infection thread was devoid of its wall. Bacteria were found to be encircled by plasmalemma invaginations forming "symbiosomes". Lipid bodies were present near the membrane of the infection thread, close to the site of bacterial release, and in close association with plasmalemma.