Underwater light climate and the growth and pigmentation of planktonic blue-green algae (Cyanobacteria) II. The influence of light quality

Abstract

The influence of light quality on the growth and chlorophyll and phycobiliprotein composition of eight strains of planktonic blue-green algae has been investigated. Growth rate in chromatic (red, green, blue) light (12 μE m -2 s -1 ) (1 μE = 6 × 10 17 photons) is a general function of the light absorption capacity of the cell. In all strains examined growth rate is enhanced in red light, and in Oscillatoria redekei and Gloeotrichia echinulata CC1 it exceeds the maximum growth rate possible in white light of a higher photon flux density under otherwise similar experimental conditions. In green light the growth rate of six phycocyanin-rich strains is approximately 60–75% of that in white light (12 μE m -2 s -1 ), but growth rate is enhanced in O. agardhii 7821 and G. echinulata CC1, which synthesize the green-light-absorbing phycobiliprotein, phycoerythrin. With the exception of these two phycoerythrin-producing strains, incubation in blue light results in a pronounced reduction in growth rate, which in the majority of strains is associated with a specific decline in cell chlorophyll concentrations. In all strains cell chlorophyll and phycobiliprotein content is similar in both white and green light. Associated with the enhancement of growth rate in red light there is a general decline in cell pigment concentrations. An increase in the cell chlorophyll: phycobiliprotein ratio also occurs in a number of strains in red light. This qualitative variation in pigmentation occurs where growth rate is at or near its maximum rate and in Gloeotrichia echinulata CC1 is the result of a specific reduction in the rate of phycoerythrin synthesis. In contrast to other blue-green algae capable of chromatic adaptation, the modulation of phycoerythrin synthesis in this strain is influenced considerably by the photon flux density of red light.