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The green alga Scenedesmus sp. was exposed to a long-term physiological stress of 40 days induced by the combination of nitrate deficiency, different concentrations of sodium chloride, and high light irradiance. Under these conditions, the change of photosystem II (PSII) photochemical reactions of photosynthesis and cellular growth were investigated along with the synthesis of secondary carotenoids, including astaxanthin and canthaxanthin. From 10 to 40 days, the biosynthesis of these secondary carotenoids was highly induced after the deterioration of PSII complexes when chlorophyll synthesis and cell division were inhibited. In this long term study, the highest induction of carotenoid synthesis happened after the deterioration of PSII reaction centers. There was no direct relationship between the induction of secondary carotenoids and the decline of PSII photochemical efficiency, although it may contribute to carotenogenesis. Under this stressful condition, viability of cells was noted by the small change of unbleached cell density compared with control after 40 days. Therefore, Scenedesmus sp. was tolerant to the long-term chronic stress condition caused by the production of secondary carotenoids, such as astaxanthin and cantaxanthin, participating in antioxidative mechanisms to protect algal cellular system. Key words: photosystem II, green algae, Scenedesmus sp., secondary carotenoids, salt stress, carotenogenesis. L'algue verte Scenedesmus sp. a ete exposee a un stress physiologique a long terme de 40 jours, en combinant un deficit en nitrate, differentes concentrations en chlorure de sodium et une forte irradiance lumineuse. Dans ces conditions, les auteurs ont examine le changement des reactions photochimiques du photosysteme II (PSII) de la photosynthese et la croissance cellulaire, ainsi que la synthese de caroteno'ides secondaires, incluant l'astaxanthine et la canthaxantine. Du 10e au 40e jour, les auteurs ont observe une forte induction de la biosynthese de ces caroteno'ides secondaires qui a ete induite apres la deterioration des complexes du PSII, alors que la synthese de la chlorophylle et la division cellulaire etaient inhibees. Dans cette etude a long terme, la plus forte induction de la synthese des caroteno'ides est survenue apres la deterioration des centres reactionnels du PSII. Les auteurs n'ont observe aucune relation directe entre l'induction des caroteno'ides secondaires et le declin de l'efficacite photochimique du PSII, bien qu'il puisse contribuer a la carotenogenese. Sous cette condition stressante, les auteurs ont constate la viabilite des cellules par un petit changement de la densite des cellules non delavees, comparativement aux temoins, apres 40 jours. Consequemment, Scenedesmus sp. s'est avere tolerant a la condition de stress chronique a long terme, par la production de caroteno'ides secondaires, comme l'astaxanthine et la cantaxanthine, participant a des mecanismes antioxydants pour proteger le systeme cellulaire des algues. Mots-cles : photosysteme II, algue verte, Scenedesmus sp., caroteno'des secondaires, stress salin, carotenogenese. [Traduit par la Redaction], Introduction Under optimal physiological conditions, green algae synthesize different pigments in the chloroplast such as chlorophylls a and b, and also carotenoids including (β-carotene, neoxanthin, violaxanthin, and zeaxanthin, which have [...]

The toxicity effect of silver nanoparticles (AgNPs) on growth and cellular viability was investigated on the aquatic plant Lemna gibba exposed over 7 d to 0, 0.01, 0.1, 1, and 10 mg/L of AgNPs. Growth inhibition was demonstrated by a significant decrease of frond numbers dependent on AgNP concentration. Under these conditions, reduction in plant cellular viability was detected for 0.1, 1, and 10 mg/L of AgNPs within 7 d of AgNPs treatment. This effect was highly correlated with the production of intracellular reactive oxygen species (ROS). A significant increase of intracellular ROS formation was triggered by 1 and 10 mg/L of AgNP exposure. The induced oxidative stress was related to Ag accumulation within L. gibba plant cells and with the increasing concentration of AgNP exposure in the medium. The authors' results clearly suggested that AgNP suspension represented a potential source of toxicity for L. gibba plant cells. Due to the low release capacity of free soluble Ag from AgNP dissolution in the medium, it is most likely that the intracellular uptake of Ag was directly from AgNPs, triggering cellular oxidative stress that may be due to the release of free Ag inside plant cells. Therefore, the present study demonstrated that AgNP accumulation in an aquatic environment may represent a potential source of toxicity and a risk for the viability of duckweeds. Environ. Toxicol. Chem. 2013;32:902-907. © 2013 SETAC [ABSTRACT FROM AUTHOR]

Abstract: The toxicity effects of silver (Ag) and the protective role of calcium chloride (CaCl2) was studied in Lemna gibba L. (L. gibba) plants. Silver speciation showed that silver toxicity in L. gibba culture medium can be attributed to free ionic Ag+ concentration. Frond abscission, intracellular reactive oxygen species (ROS) formation and intracellular uptake of Ag+ were investigated when L. gibba plants were exposed to AgNO3 concentrations (0.5, 1, 5, and 10 μM) supplemented or not by 10 μM CaCl2. An increase in frond abscission, intracellular ROS and intracellular uptake of Ag+ were detected in L. gibba plants for all tested concentrations of AgNO3 after 24 h treatment. However, addition of 10 μM CaCl2 to the L. gibba culture medium reduced the toxic effects of Ag by decreasing silver uptake into the plant and intracellular ROS formation. The results suggest that Ag-induced toxicity was attributed to Ag+ accumulation and chloride was able to protect L. gibba plants against Ag toxicity by formation of complexes with Ag and then alleviation of the metal induced oxidative stress. [Copyright &y& Elsevier]

Carotenoids have potent antioxidant activity as well as therapeutic value, and their formation has been seen to be induced in algae by stress, including high-salt culture conditions. A differential profiling of carotenoids was conducted using a targeted metabolomics approach with accurate mass data generated by liquid chromatography-electrospray-time-of-flight (LC-ESI-TOF) mass spectrometry followed by postacquisition filtering based on isotope patterns and mass defects to detect carotenoids up-regulated in Scenedesmus sp. exposed to high-salt conditions. Algal cultures treated with high concentrations of sodium acetate or sodium chloride were found to cause an increase in various carotenoids. On the basis of differential analysis, astaxanthin and canthaxanthin increased upon salt treatment. Astaxanthin, in its free form and as fatty acid esters, was seen to increase in Scenedesmus sp. using accurate mass MS. A few other carotenoid compounds increased upon salt treatment, including echinenone and adonirubin, involved in the pathway of astaxanthin biosynthesis from β-carotene, as well as isomers of astaxanthin and canthaxanthin. A time course study of acetate treatment was done to observe the time-dependent up-regulation of carotenogenesis.