Verification of cell specificity of RNA extractions by RT-qPCR. rbcL and nifK were used as the probes for genes expressed specifically (see text) in vegetative cells (rbcL, top panel) and in heterocysts (nifK, bottom panel). The internal standard was rnpB, which is expressed constitutively in all cells. Culture conditions are shown in white (phototrophic), gray (mixotrophic), and black (heterotrophic). V: RNA extracted from vegetative cells; Ht: RNA extracted from heterocysts. Means and standard deviations are based on three biological replicates. Transcript levels are normalized to 1 in heterocysts (rbcL) and in vegetative cells (nifK).