COLONIZATION OF WHEAT (TRITICUM-VULGARE L) BY N2-FIXING CYANOBACTERIA .2. AN ULTRASTRUCTURAL-STUDY

The ultrastructure of a novel association between a N2-fixing cyanobacterium, Nostoc sp. isolated from soil, and wheat seedlings grown in liquid culture is described. Cyanobacteria were found either as hormogonia, filaments or aseriate packages. The aseriate packages, which developed from filaments, often formed a thick layer surrounding the root surface. The packages were in intimate contact with adjacent root epidermal cells and could not be removed without damaging the epidermis. Cyanobacteria penetrated both the root epidermis and cortex and formed packages in intercellular spaces. Cyanobacterial filaments were occasionally found within plant cells that appeared empty. Additionally, cyanobacteria were observed in association with the stem and on the surfaces of leaves. These findings demonstrate the technical feasibility of forming a novel association between a N2-fixing cyanobacterium and a cereal.