Acclimation of Synechococcus strain WH7803 to ambient CO2 concentration and to elevated light intensity

A CO2 concentrating mechanism has been identified fn the phycoerythrin-possessing Synechococcus sp. WH7803 and has been observed to be severely inhibited by short exposure to elevated light intensities. A light treatment of 300-2000 mu mol quanta . m(-2). s(-1) resulted in a considerable decay in the variable fluorescence of PSII with time, suggesting decreased efficiency of energy transfer from the phycobilisomes, direct damage to the reaction center II, or both. Measurements of the activity of PSII and changes in fluorescence emission spectra during a light treatment of 1000 mu mol quanta . m(-2). s(-1) indicated considerable reduction In the energy flow from the phycocyanin to the phycobilisome terminal acceptor and chlorophyll a. Consequently, whereas the maximal photosynthetic rate, at saturating light and Co-2 concentration, was hardly affected by a light treatment of 1000 mu mol quanta . m(-2). s(-1) for 2 h, the light intensity required to reach that maximum increased with the duration of the light treatment.