Abstract
Heterokont algae are significant contributors to marine primary productivity. These algae have a photosynthetic machinery that shares many common features with that of Viridiplantae (green algae and land plants). Here we demonstrate, however, that the photosynthetic machinery of heterokont algae responds to light fundamentally differently than that of Viridiplantae. While exposure to high light leads to electron accumulation within the photosynthetic electron transport chain in Viridiplantae, this is not the case in heterokont algae. We use this insight to manipulate the photosynthetic electron transport chain and demonstrate that heterokont algae can dynamically distribute excitation energy between the two types of photosystems. We suggest that the reported electron transport and excitation distribution features are adaptations to the marine light environment.
Highlights
Heterokont algae have emerged as the result of a secondary endosymbiotic event [1,2] and dominate carbon fixation within the oceans [3,4]
In order to determine whether bright light pulses completely reduce the plastoquinone pool, and induce the maximum fluorescence yield, we employed a reference condition that is known to result in a reduced photosynthetic electron transport chain
While C. reinhardtii is considered a model for plants concerning excitation distribution between the two photosystems, it is noteworthy that, especially in the presence of acetate in the growth medium, chlororespiration is uniquely prominent in this alga [14], a feature shared with the diatom P. tricornutum [15,16]
Summary
Heterokont algae have emerged as the result of a secondary endosymbiotic event [1,2] and dominate carbon fixation within the oceans [3,4]. Separated by more than a billion years of evolution from a common ancestor, the photosynthetic machinery of Viridiplantae (green algae and land plants) and heterokont algae retains common features [2]. Both groups of organisms have two types of photosystems, which are linked by an electron transport chain that includes a pool of plastoquinone molecules. Another common feature is the presence of light-harvesting complexes, which house chlorophylls and carotenoids. A interesting question is how these organisms utilize differences in their photosynthetic machineries to respond to the environmental conditions they encounter
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