Adaptations inOscillatoria redekeiat very slow growth rates—changes in growth efficiency and phycobilin complement

The planktonic cyanophyte Oscillatoria redekei van Goor was grown in a range of light-dark cycles of 1-h duration under quantum irradiances of 8 and 21 μmol m-2s-1. The cells were “low-light adapted” even at the highest light exposures and between 0·67 and 0·3 mol m-2d-1, growth rate declined linearly with light exposure. At light exposures below 0·3 mol m-2d-1, the plot of growth rate on light exposure deviated from a straight line and curved towards the origin. At these very low growth rates, the cells showed greater overall light interception due to a pronounced increased in phycoerythrin. The implication of these results is that “maintenance energy” is a mathematical abstraction and the “cost” of maintaining a cell varies with growth rate.