A Mechanistic Study of CO\(_{2}\) Fixation in Marine Diatoms: Effects of Diel Cycling, Temperature and Light Intensity on Thalassiosira Weissflogii

Abstract

The effects of 12 hour light: 12 hour dark diel cycling, temperature (19.1, 23.5, 25.3°C), and light intensity (190, 323, 459 μmol m-\(^{2}\) s-\(^{1}\)) on the CO\(_{2}\) fixation mechanism in the model diatom Thalassiosira weissflogii were examined in this study. Strong diel periodicities in protein concentrations indicate a daily process of synthesis and degradation of cellular machinery for metabolic functions. Discrepancies between the periodicities observed in RuBisCO, CdCA abundances, and GPP rates suggest that regulation of CO\(_{2}\) fixation is not influenced by abundances of these proteins but possibly by: relocalization of RuBisCO from stroma to pyrenoid, activation of RuBisCO activase upon light exposure, and anaplerotic and/or supplementary C\(_{4}\) carbon fixation. CdCA appears to play a larger role in late-photophase and scotophase following up-regulation at midday, when CO\(_{2}\) equilibration from bottle headspace to seawater media is outpaced by peak growth rates. Consistent NPP rates with increasing temperature may be due to RuBisCO’s tendency to produce dead-end complexes, coupled with RuBisCO activase’s sensitivity to heat stress, and to assimilate O\(_{2}\) for photorespiration. Consistent NPP rates may be sufficient in supporting faster growing cells with smaller volume at higher temperatures, which may also facilitate vegetative reproduction. Under high light intensity, photo-acclimated responses include decreased PS II concentrations or reduction in the size of photosystems (e.g. number of terminals). Diatoms like T. weissflogii appear to rapidly adapt to immediate environmental fluctuations, as well as readily acclimate to long-term conditions. Such flexible physiological responses contribute to its ecological success and perhaps, even its ability to continuously thrive in changing marine environments with the effects of global climate change.