FIG. 3.

Inactivation of hetY produced immature and abnormal heterocysts, as shown in photomicrographs of wild-type Anabaena strain PCC 7120 (A and C) and hetY-inactivated strain AMC642 (B and D) taken before (A and B) and 24 h after (C and D) heterocyst induction. Arrowheads mark heterocysts that are mature in the wild type (C) but immature (lacking polar cyanophycin granules) and abnormal in the hetY mutant (D). The arrow indicates defective vacuolated heterocyst morphology occasionally produced by strain AMC642. Bar, 5 μm.