Figure 5.

The effects of soluble sugars on N. punctiforme hormogonia differentiation. N. punctiforme was induced to form hormogonia (i.e. the rod-shaped filaments in the top panels) by streaking cells from a dense culture onto fresh N-free solid medium supplemented with 30 mm of the indicated sugar or with no sugar. Streaking was confined to the center of the plate, marked by a red circle (1 cm in diameter) visible in some bottom panels. Nostoc filaments differentiated into hormogonia after overnight incubation on fresh medium; however, the frequencies of subsequent hormogonia formation varied, depending on the specific sugar present in the media. Pictures of the culture were taken under a stereo microscope 3 weeks (top panels) or 5 weeks (bottom panels) after initial hormogonia induction. The magnifications of the top and bottom panels were approximately 64× and 7.5×, respectively. The red and blue dots on the bottom panels were used to mark the extent of hormogonia movement at the end of the first week.