Adaptation to low photon flux densities in Protogonyaulax tamarensis var. excavata,with reference to chloroplast photomorphogenesis

Changes in cellular chlorophyll content, cell volume, and light scatter of a New England red tide dinoflagellate, Protogonyaulax tamarensis var. excavata (clone GT-429), cultured in various light regimes are reported. Individual cells were analyzed, using flow cytometry and compared to traditional bulk measurements. Compared to high photon flux densities (182 Ein m^-2 s^-1), changes were measured that reflected increased chlorophyll fluorescence and increased cell volume at reducec photon flux densities when cell division was sustained, and increased flourescence and decreased cell volume when cell division ceased. These optical changes were accompanied by conformational changes in the chloroplasts. We found no change in photosynthetic carboxylating enzyme activities. We suggest that this photomorphogenesis of the chloroplasts at low photon flux densities may be an indication of stress and survival vs adaptive value to these persistent cells.