Photosynthesis in Chromera velia Represents a Simple System with High Efficiency

Abstract

Chromera velia (Alveolata) is a close relative to apicomplexan parasites with a functional photosynthetic plastid. Even though C. velia has a primitive complement of pigments (lacks chlorophyll c) and uses an ancient type II form of RuBISCO, we found that its photosynthesis is very efficient with the ability to acclimate to a wide range of irradiances. C. velia maintain similar maximal photosynthetic rates when grown under continual light-limited (low light) or light-saturated (high light) conditions. This flexible acclimation to continuous light is provided by an increase of the chlorophyll content and photosystem II connectivity under light limited conditions and by an increase in the content of protective carotenoids together with stimulation of effective non-photochemical quenching under high light. C. velia is able to significantly increase photosynthetic rates when grown under a light-dark cycle with sinusoidal changes in light intensity. Photosynthetic activities were nonlinearly related to light intensity, with maximum performance measured at mid-morning. C. velia efficiently acclimates to changing irradiance by stimulation of photorespiration and non-photochemical quenching, thus avoiding any measurable photoinhibition. We suggest that the very high CO2 assimilation rates under sinusoidal light regime are allowed by activation of the oxygen consuming process (possibly chlororespiration) that maintains high efficiency of RuBISCO (type II). Despite the overall simplicity of the C. velia photosynthetic system, it operates with great efficiency.

Violaxanthin inhibits nonphotochemical quenching in light‐harvesting antenna of Chromera velia

“…The pigment composition of fractions 1–3 was determined by HPLC. This analysis revealed the presence of three main pigments for this alga : chlorophyll a (approximately 50%), isofucoxanthin (approximately 30%) and violaxanthin (approximately 10%) (Table ). There was no zeaxanthin detected because we used dark‐adapted cells to avoid de‐epoxidation of violaxanthin into zeaxanthin .…”

Role of Ions in the Regulation of Light-Harvesting

“…A similar mechanism for NPQ has been proposed for desiccating mosses and lichens (Yamakawa et al, 2012; Slavov et al, 2013). This could be a typical photoprotective NPQ mechanism during desiccation (Bilger, 2014) or in certain algae it could be due to a high spillover of energy from PSII to PSI (see e.g., data obtained with algae C. velia Quigg et al, 2012; Kotabová et al, 2014). Further, data of Ruban and Horton (1995) indicate that pH-independent fraction of sustained quenching can be inhibited by the addition of nigericin, a K + /H + uncoupler.…”

The Organellar Genomes of Chromera and Vitrella, the Phototrophic Relatives of Apicomplexan Parasites

“…Because transcripts are not oligouridylylated in the apicoplast of Plasmodium, an intriguing link between the oligoU-tailed transcripts of phototrophic genes in Chromera and the loss of photosynthesis in Apicomplexa was recently proposed (13). Despite a greatly mutated plastid genome (31) and a reduced set of photosystem proteins (H. Esson, A. Horák, P. Dufková, R. Sobotka, P. Komenda & M. Oborník, unpublished data), Chromera is highly efficient at photosynthesis-likely because it can acclimatize to different light conditions (3,42,43,48,64) and because nonphotochemical quenching protects it very effectively from excessive radiation (43,48). The main light-harvesting complex of Chromera contains chlorophyll a, violaxanthin, and a yet-unidentified carbonyl isofucoxanthin-related carotenoid, and its energy transfer from carotenoid to chlorophyll a is more efficient than any seen among the investigated FCP (fucoxanthin chlorophyll protein)-like proteins (14).…”