CHANGES IN THE PIGMENT CONTENT OF ANABAENA-VARIABILIS CELLS IN OUTDOOR CULTURE

The influence of daily and seasonal irradiance as well as of other environmental factors on the pigment content of the nitrogen-fixing blue-green alga Anabaena variabilis has been investigated in outdoor cultures. An adaptive response to variations in solar irradiance is evident throughout day-night cycles and during the months of high and low solar irradiance, the chlorophyll level of the cells increasing when irradiance decreases. A similar adaptive reaction to indirect changes in the availability of light to cells caused by variations in either density or depth of the cell suspension has also been observed. The accessory pigments phycobiliproteins respond in an analogous manner. Growth rate estimates in A. variabilis outdoor cultures significantly differ depending on whether growth is expressed on either a chlorophyll or a dry weight basis. This discrepancy is due to the variability in the chlorophyll content of cells in response to either direct or indirect changes in available light.