Long-term stress induced by nitrate deficiency, sodium chloride, and high light on photosystem II activity and carotenogenesis of green alga Scenedesmus sp

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 [...]