Decay of delayed light with the diatom Phaeodactylum tricornutum

Abstract

Intact cells of the diatom Phaeodactylum tricornutum do not show a smooth afterglow decay curve. After a sharp decline (0–150 msec), a maximum may occur after 4 sec at 17° or after 22 sec at 2°. This maximum is present after excitation with far red light of low intensity, which is absorbed primarily by photosystem I. It appears to be structure-bound: cell disintegration causes its disappearance, while the 150 msec afterglow component is much less affected. The maximum also disappears after addition of 3-(3′4′-dichlorophenyl)-1,1-dimethylurea (DCMU) or ammonium chloride, but it remains unaffected by addition of phenazinemethosulphate (PMS) or pyocyanin. Addition of DCMU results in a strong increase in the 150 msec afterglow when the cells are excited with far red light. The experiments suggest that a diffusion-limited energy transfer mechanism, depending on the physiological state of the cell, is responsible for the maximum.