Abstract
Little is known on the antioxidant activity modulation in microalgae, even less in diatoms. Antioxidant molecule concentrations and their modulation in microalgae has received little attention and the interconnection between light, photosynthesis, photoprotection, and antioxidant network in microalgae is still unclear. To fill this gap, we selected light as external forcing to drive physiological regulation and acclimation in the costal diatom Skeletonema marinoi. We investigated the role of light regime on the concentration of ascorbic acid, phenolic compounds and among them flavonoids and their connection with photoprotective mechanisms. We compared three high light conditions, differing in either light intensity or wave distribution, with two low light conditions, differing in photoperiod, and a prolonged darkness. The change in light distribution, from sinusoidal to square wave distribution was also investigated. Results revealed a strong link between photoprotection, mainly relied on xanthophyll cycle operation, and the antioxidant molecules and activity modulation. This study paves the way for further investigation on the antioxidant capacity of diatoms, which resulted to be strongly forced by light conditions, also in the view of their potential utilization in nutraceuticals or new functional cosmetic products.
Highlights
Aerobic organisms need to deal with reactive oxygen species (ROS) which are harmful to their metabolism since high ROS concentrations can damage cellular machinery threatening cell survival; simultaneously ROS play a role as secondary messengers
Being light a crucial ecological axis in ruling the metabolism of photosynthetic organisms, and modulating the growth, the objective of this study was to investigate the impact of light intensity, photoperiod, and wave light distribution on the cellular concentrations of antioxidant molecules such as ascorbic acid (AsA) and flavonoids, and total phenolic content
After 24 h from the light shifts, in all the experimental conditions the growth rate of S. marinoi decreased (Table 2), in contrast with what observed in the control condition, revealing a physiological stress induced by the variations of light environment
Summary
Aerobic organisms need to deal with reactive oxygen species (ROS) which are harmful to their metabolism since high ROS concentrations can damage cellular machinery threatening cell survival; simultaneously ROS play a role as secondary messengers. The balance between toxicity, when ROS are in excess, and the signaling action requires cells to finely tune the ROS concentration [2,3,4], thanks to an efficient intracellular network composed by antioxidant molecules and enzymes. Antioxidants include molecules such as ascorbic acid (AsA), carotenoids, glutathione (GSH), tocopherols as well as phenolic compounds. Carotenoids occur in the chloroplast membranes interacting directly where photosynthesis-derived ROS are generated.
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