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EVIDENCE FOR CALCIUM‐MEDIATED REGULATION OF HETEROCYST FREQUENCY AND NITROGENASE ACTIVITY IN NOSTOC 6720
Author(s) -
SMITH R. J.,
HOBSON S.,
ELLIS I. R.
Publication year - 1987
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1987.tb00891.x
Subject(s) - heterocyst , nitrogenase , extracellular , calcium , nostoc , biology , lanthanum , intracellular , biochemistry , ionophore , cyanobacteria , biophysics , chemistry , nitrogen fixation , inorganic chemistry , bacteria , membrane , genetics , organic chemistry
S ummary The proportion of heterocysts (heterocyst frequency) in cultures of Nostoc 6720 varied with the Ca 2+ concentration present in the growth medium, the proportion increasing from 5 to 9 % as the Ca 2+ concentration was increased from 10 −5 to 10 −4 M. The total nitrogenase activity of the culture declined by 20% whereas the activity per heterocyst decreased by 30%. In the 10 −4 to 10 −3 M range of Ca 2+ concentrations, which includes those employed in most standard media, the heterocyst frequency and nitrogenase activity did not change. At Ca 2+ concentrations above 2 × 10 −3 M the heterocyst frequency decreased and this decrease was associated with a lower growth rate. The presence of the calcium ionophore A23187 increased the heterocyst content of the culture and total nitrogenase activity, but still decreased the nitrogenase activity per heterocyst. The effects of A23187 and Ca 2+ concentration were additive and demonstrated a positive interaction between Ca 2+ and the ionophore. In contrast, the Ca 2+ antagonist, lanthanum, decreased the heterocyst frequency and, at concentrations below 10 −8 M, stimulated nitrogenase activity. At higher concentrations of lanthanum, growth, heterocyst frequency and nitrogenase activity were markedly diminished; cell degradation occurred at concentrations in excess of 10 −4 M. An analysis of the intra‐ and extracellular binding of 45 Ca 2+ showed that decreasing the Ca 2+ concentrations in the medium from 10 −4 to 10 −5 M lowered the intracellular Ca 2+ content. In the presence of A23187, intracellular Ca 2+ increased. The lanthanum treatment was exceptional in that the intracellular Ca 2+ was increased about four‐fold. These results are interpreted as favouring the hypothesis that a Ca 2+ ‐mediated regulatory process modulates heterocyst frequency and nitrogenase activity in Nostoc 6720.