Summary: The fragmentation of filaments resulted in the induction of a synchronous round of heterocyst differentiation. Young heterocysts (proheterocysts) appeared 12 to 15 h after fragmentation, and 12 to 15% of the cells became heterocysts within 24 h. NHCl or NaNO prevented the formation of new heterocysts, while differentiation was stimulated twofold by the absence of atmospheric N. The sequence of appearance of heterocyst-specific characteristics was observed following filament fragmentation. Nitrogenase activity increased rapidly between 13 and 26 h, paralleling the increase in heterocyst frequency. Glycolipids unique to the heterocyst envelope were also synthesized between 13 and 26 h, and activities of 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase increased after 10 h and 90 h respectively. Aged medium induced sporulation in intact filaments within 1 d. but sporulation could occur no earlier than 2 d after filament fragmentation, indicating that the induction of sporulation requires the presence of mature (but not necessarily functional) heterocysts.


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