Interaction of boron and calcium in the cyanobacteria Anabaena and Synechococcus

Although some studies have reported an interaction between boron (B) and calcium (Ca 2+ ) in higher plants, there is little evidence for a similar relationship in cyanobacteria. The present study was designed to determine the effect of a supplement of boron to Ca 2+ ‐deficient cultures of Anabaena PCC 7119 and Synechococcus PCC 7942. Grown under Ca 2+ deprivation, Anabaena had a slow growth rate and a low photosynthetic pigment content that was related to an inhibition of photosynthesis. Ca 2+ ‐deficient cells showed a lack of cohesiveness of the heterocyst envelope layers, which was consistent with a rapid decline in nitrogenase activity. A supplement of B led to partial recovery from the effects caused by lack of Ca 2+ . Similarly, low Ca 2+ had inhibitory effects on growth and metabolism of Synechococcus cultures. In this case, the effect of a B supplement depended on the concentration of Ca 2+ in the growth medium. When Ca 2+ was present at normal concentration. B was not required, at least no more than trace amounts. However, when the Ca 2+ concentration decreased, B was required at increasing levels. An effect of boron on uptake and/or on the binding of Ca 2+ in cyanobacteria is proposed.