Photoprotective capabilities of marine microalgae: Xanthophyll-cycle pigment and photosystem II fluorescence responses under static and dynamic irradiance regimes

Adjustments of an algal cell's photosynthetic capabilities occur over many time scales; those which involve de novo synthesis of proteins and pigments and occur over hours to days are termed “photoacclimatory”, while those which usually do not involve de novo synthesis and occur more rapidly are often referred to as “photoprotective”. We have a good understanding of the photoacclimatory adjustments of algae at steady-state. These responses are well characterized and somewhat predictable. However, the photophysiological responses of algae under nonsteady-state conditions, which are more indicative of the in situ environment, are less well characterized. The work presented in this dissertation is primarily concerned with how algae produce the optimal photophysiological posture for light fields, which are not at steady state. This is the crux of dynamic photoacclimation, which determines the photoprotective capabilities, which in turn prevent or mitigate photoinhibition whilst simultaneously assuring optimal photosynthetic rates.; Several investigations are presented in which we attempt to explore the effects of various light fields upon the photoacclimatory responses of the Florida red-tide dinoflagellate, Gymnodinum breve, and the marine diatom Phaeodacylum tricornutum. Particular emphasis has been placed upon the photoprotective capabilities, especially that of the xanthophyll-cycle mediated, non-photochemical fluorescence quenching response. A variety of static and dynamic-irradiance conditions have been employed in order to explore how the quality, quantity and rate of change of the light driving photosynthesis determines photoprotective functionality.; Results indicate that marine microalgae exhibit robust photoprotective capabilities, which are capable of responding to high irradiance intensities and on time scales relevant to highly dynamic irradiance fluctuations. Furthermore, photoacclimatory responses to dynamic growth irradiance are significantly different than those responses to static growth irradiances. The suitability of particular photoacclimatory states to respond to changes in light regimes is addressed. Additionally, a novel analytical photobioreactor, which is capable of generating irradiance fluctuations similar to in situ variations, is described.