FIG. 1.

Acclimation of Frankia sp. strain CcI3 cells to nitrogen-free conditions shown by the time course of acetylene reduction activity (A), nitrogen fixation vesicle formation (B), and nifH expression (C). (A) Acetylene reduction activity was measured in strain CcI3 grown in BAP medium containing 5 mM NH₄Cl (N⁺, closed circles) or without a nitrogen source (N⁻, open circles). Error bars represent standard deviations (n = 2). (B) Photomicrographs of the Frankia cells were taken at 6 dat to N⁺ (top) or N⁻ (bottom) conditions. Arrows indicate vesicles. Bars, 1 μm. (C) qRT-PCR of the nifH gene was performed using total RNA extracted from the cells at 6 dat to N⁺ or N⁻ conditions. Error bars represent standard deviations (n = 3).