Photoacclimation of Prymnesiales (Haptophyta) species to different light quality conditions.

Supervisor: Sergio Seoane (PiE-UPV/EHU).
Light conditions under water vary considerably in terms of both quality and quantity due to the depth with the wavelength-dependent extinction coefficients, the weather with clouds passing over, the day length and other factors. The photoacclimation response aims to balance the light-harvesting and the photoprotective capacities together in order to maximize cellular activities including photosynthesis. Therefore, it participates in the competitive ability of a species through the growth and the survival and plays a substantial role in the presence or absence of a species in a determined habitat. This process involves different chemical and or biological modifications depending on the timescale. In fact, photoacclimation processes are sorted into two categories depending on their short- or long-term dynamics. This study aimed to investigate both short- and long- term mechanisms through respectively the xanthophyll cycle, with diadinoxanthin and diatoxanthin, and the adjustment of the composition in the other pigments to different light quality in Prymnesiales that present a huge variety of pigments with light-harvesting or photoprotective properties. Among those molecules, Chlorophyll a, different chlorophylls c such as Chl c3, and fucoxanthins belonging to the light-harvesting category as well as ß,ß-carotene, which has a photoprotective role, were studied. In order to carry out this study, a range of Prymnesiales species representing different pigment types were grown under different light spectra through white fluorescent light as well as white, red, blue and green LED lights. Subsequently, HPLC analyses were performed to determine the presence as well as the amount of extracted pigments from the algae harvested at the end of the exponential phase. Then observed changes could be related to the light environment in coastal and open-ocean waters, which usually display spectra richer respectively in green and blue wavelengths. Then, a substantial peak of the ratio 4-keto-19’-hexanoyloxyfucoxanthin to Chl a was highlighted under blue light conditions in HAPTO-7 species (Chrysochromulina rotalis and Haptolina hirta). Moreover the growth was impacted with the lowest specific growth rate observed under red light conditions.

Haptophyta – Prymnesiales – Light quality – Pigments – Fucoxanthin – Chlorophylls – Growth rate