The pattern of acetylene reduction by cyanobacteria grown under alternating light and darkness

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Abstract
When N2-fixing cyanobacteria were grown under alternating 12 h light and 12 h darkness, three patterns of acetylene reduction were observed. All non-heterocystous species reduced acetylene either mainly or exclusively in the dark. This pattern of acetylene reduction may have a role in the protection of nitrogenase from photosynthetically generated O2. On the other hand all heterocystous species reduced acetylene either mainly in the light or both in the light and the dark, though usually at higher rates in the light.