Variability of spectral absorption efficiency within living cells of Pyrocystis lunula (Dinophyta)

This study examines variability in the spectral absorption efficiency in various parts of living Pyrocystis lunula cells. changes in spectral absorption efficiency measured within cells are attributed to light-induced chloroplast migration as well as reorganization of cellular material during the process of asexual reproduction. During the dark cycle, major pigment peaks were well resolved in those spectra measured in the distal cytoplasmic strands where chloroplasts were concentrated. In contrast, the absorption efficiencies measured in the granular central area that did not contain chloroplasts decreased gradually from the blue to the red portions of the spectrum and are similar to those published for detrital particles. When chloroplasts migrated toward the center of the cell in response to light, absorption efficiency curves for the granular central area were flatter than the curves measured in cytoplasmic strands containing chloroplasts. This was due to the combined absorption properties of the central area and the chloroplasts. Absorption efficiency spectra were also flattened in aplanospores within the parent vegetative cells because of the concentration of cellular material into smaller areas. These findings suggest that shapes of spectral absorption curves measured for the major phytoplankton groups cannot be assumed to remain constant over time. Furthermore, changes in cell structure may account for some of the reported diel changes in beam attenuation and stimulated fluorescence in natural waters.