Azolla-Anabaena azollae Relationship: IV. Photosynthetically Driven, Nitrogenase-catalyzed H(2) Production.

The water fern, Azolla caroliniana Willd., containing the symbiotic, heterocystous blue-green alga, Anabaena azollae, has been studied under various growth conditions to characterize its light-dependent production of H(2). The response of H(2) production to N(2) and C(2)H(2) and the absence of a differential effect of m-chlorocarbonyl cyanide phenylhydrazone on H(2) production and C(2)H(2) reduction, coupled with the parallel inhibition of both processes by DCMU imply that the production of H(2) is nitrogenase-catalyzed and ATP-dependent.H(2) was produced by fronds grown under air-CO(2) in the presence or absence of combined nitrogen. When cultured under argon-O(2)-CO(2), only those fronds provided with combined nitrogen remained viable and produced H(2). Fronds grown on nitrate under air plus 2% CO also produced H(2). In comparison to fronds grown on N(2) alone, fronds grown on nitrate had an increased rate of H(2) production relative to C(2)H(2) reduction, and the inhibition of H(2) production by air was less.CO in argon +/- CO(2) resulted in a partial inhibition of H(2) production, whereas CO in argon-CO(2)-C(2)H(2) enhanced H(2) production in fronds grown without combined nitrogen. Our studies strongly indicate that H(2) production is nitrogenase-catalyzed but the possibility that the symbiont contains a hydrogenase cannot be totally excluded.