Mechanical damage of roots provides enhanced colonization of the wheat endorhizosphere by the dinitrogen-fixing cyanobacterium Nostoc sp. strain 2S9B

When wheat (Triticum aestivum L.) seedlings are co-cultivated with Nostoc sp. strain 2S9B in hydroponics, the cyanobacterium colonizes the endorhizosphere at low frequency. Mild sonication of the roots dramatically increased the number of cyanobacteria within the root tissue. The cyanobacteria penetrated the roots in the form of motile filaments (hormogonia), and once inside, they divided and transformed into aseriate packages, which showed nitrogenase activity. Cyanobacteria were found in the intercellular spaces as well as inside the epidermal and cortex cells. By prolonging the sonication time the number of cyanobacterial packages inside the roots increased. However, after reaching a certain abundance the total cyanobacterial biomass within the roots did not change regardless of the sonication time. Besides sonication, other methods of root surface damage also brought about enhanced internal root colonization. Sonication of roots proved to be an efficient way of amplifying the internal root colonization by cyanobacteria and can be suggested as a method for creating a model system in non-legume plant-microbe studies.