Photosynthetic activation of the dark-acclimated diatom <i>Thalassiosira weissflogii</i> upon light exposure

Abstract

The photoresponse of chlorophyll a (Chl a) fluorescence and xanthophyll pigments to light was studied in the diatom Thalassiosira weissflogii with respect to various durations of dark storage. The light-limited slope (α) obtained from the electron transport rate (ETR) versus the irradiance curve remained steady, whereas the light-saturated rate (ETRmax) decreased gradually during dark storage. Consequently the light-saturation index (Ek=ETRmax/α) decreased with time, suggesting that cells acclimate to dark conditions. Dark-acclimated cells were exposed to light-dark conditions with varied silicate availability. The maximum quantum yield of PSII (Fv/Fm), as well as the changes in the α and the ETRmax, increased immediately to the maximum on the first day and decreased for the second half of the light exposure period. The ratio of diatoxanthin (DT) to the xanthophyll pigment diadinoxanthin (DD) and DT (DT/[DD+DT]) represents thermal dissipation behavior through non-photochemical quenching (NPQ). This study indicates that Fv/Fm and Ek are a good index to follow photoacclimation during a transition from continuous dark conditions to the L-D cycle of saturated light. This study also indicates that dark-acclimated T. weissflogii can acclimate to the growth irradiance by the enhancement of photosynthetic activity with changes in xanthophyll pigments, in relation to the dark duration and silicate availability. Such a response to light suggests that the vegetative cells of T. weissflogii could possibly proliferate at ports in the coastal zone on a global scale after ejection into high light environments from the darkness of a ship’s ballast water tank.