Diatoms are able to acclimate to frequent and large light fluctuations in the surface ocean waters. However, the molecular mechanisms underlying these acclimation responses of diaotms remain elusive. In this study, we investigated the mechanism of high light protection in marine diatom Thalassiosira pseudonana using comparative proteomics in combination with biochemical analyses. Cells treated under high light (800 μmol photons m−2s−1) for 10 h were subjected to proteomic analysis. We observed that 143 proteins were differentially expressed under high light treatment. Light-harvesting complex proteins, ROS scavenging systems, photorespiration, lipid metabolism and some specific proteins might be involved in light protection and acclimation of diatoms. Non-photochemical quenching (NPQ) and relative electron transport rate could respond rapidly to varying light intensities. High-light treatment also resulted in increased diadinoxanthin + diatoxanthin content, decreased Fv/Fm, increased triacylglycerol and altered fatty acid composition. Under HL stress, levels of C14:0 and C16:0 increased while C20:5ω3 decreased. We demonstrate that T. pseudonana has efficient photoprotective mechanisms to deal with HL stress. De novo synthesis of Ddx/Dtx and lipid accumulation contribute to utilization of the excess energy. Our data will provide new clues for in-depth study of photoprotective mechanisms in diatoms.
Algae are often used as live feed for aquatic animals and widely used in the aquaculture industry. Both algal cultivation and algal blooms can lead to algal cell aggregation. High-biomass algae will lead to the accumulation of toxic and harmful substances if they are present in algal cells, thus adversely affecting the environment or the food chain. Retinoids have been detected in algal cells, and retinoic acids and their derivatives are teratogenic in animals. However, whether retinal (RAL), a metabolite of β-carotene, is regulated by light and harmful to aquatic organisms has not been thoroughly investigated. This study focused on light-induced RAL accumulation in marine algae and its teratogenic effects in the algae-invertebrate-vertebrate food chain. The concentrations of RAL in two species of marine algae (Thalassiosira pseudonana and Tetraselmis subcordiformis), used as live feed in mariculture, were determined. Based on the differences in the accumulation of RAL in algae under different light environments, we explored retinol dehydrogenase (RDH) as the possible regulatory gene. The teratogenic effects of RAL on embryos and juveniles of marine teleost medaka (Oryzias melastigma) and brine shrimp (Artemia salina) and on food chain transmission characteristics were also explored. Our results suggest that continuous high and blue light exposure induced RDH expression, and further promoted RAL accumulation. This further amplifies the accumulation of RAL in the case of high biomass algal cultivation or algal blooms. High concentrations of RAL have teratogenic effects on vertebrate fish through the food chain due to the tolerance of invertebrates. This article could provide a warning about teratogenic effects on aquatic animals in aquaculture and algal bloom.
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