Interaction of boron and calcium in the cyanobacteria Anabaena and Synechococcus

Although some studies have reported an interaction between boron (B) and calcium (Ca²⁺) 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 Ca²⁺-deficient cultures of Anabaena PCC 7119 and Synechococcus PCC 7942. Grown under Ca²⁺ deprivation, Anabaena had a slow growth rate and a low photosynthetic pigment content that was related to an inhibition of photosynthesis. Ca²⁺-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 Ca²⁺. Similarly, low Ca²⁺ had inhibitory effects on growth and metabolism of Synechococcus cultures. In this case, the effect of a B supplement depended on the concentration of Ca²⁺ in the growth medium. When Ca²⁺ was present at normal concentration. B was not required, at least no more than trace amounts. However, when the Ca²⁺ concentration decreased, B was required at increasing levels. An effect of boron on uptake and/or on the binding of Ca²⁺ in cyanobacteria is proposed.