Figure 3. Microscopy, lipids and nifHDK expression in Anabaena mutant strains.

Filaments from bubbled, ammonium-supplemented cultures of the indicated strains were washed three times with BG11₀ medium, resuspended in BG11₀ medium and incubated under the same culture conditions for the times indicated in h. (A) Samples taken at 24 h were stained with Alcian Blue prior to being photographed under a light microscope. (B) Lipids (GI and GIII are heterocyst envelope glycolipids) were isolated and separated by TLC. (C) Total RNA was isolated and used in northern blot analysis with a probe of the nifH gene or, as a loading and transfer control, the rnpB gene. A size standard is indicated at the left and the observed transcripts at the right.