Induction of carotenoid cleavage by salt stress and the effect of their products on cell growth and pigment accumulation in Dunaliella sp. FACHB-847

Abstract

Carotenoid cleavage products (CCPs) can serve critical functions including hormones, volatiles, signals, and growth inhibitors. However, little is known about the regulation of carotenoid degradation and function of CCPs in high carotenoid-accumulating Dunaliella species. In this study, high salt stress resulted in high accumulation of CCPs including α-ionone, β-ionone and β-cyclocitral in Dunaliella sp. FACHB-847. Under salt stress, carotenoid degradation of Dunaliella sp. was dependent of the expression levels of carotenoid cleavage dioxygenase genes to some extent and may occur mostly non-enzymatically. Exposure of Dunaliella cells to exogenous β-ionone and β-cyclocitral (10 mg/L) induced the generation of reactive oxygen species, enhanced malondialdehyde levels, decreased cell growth and chlorophylls, and down-regulated genes involved in carbon metabolism, biosynthesis of amino acid, and energy metabolism related to cell development and growth. β-ionone and β-cyclocitral also repressed carbon fixation and chlorophyll biosynthesis, which was in agreement with the decreased chlorophylls. β-ionone up-regulated genes involved in the biosynthesis of cellular membrane due to the severe cell damage. β-cyclocitral down-regulated genes responsible for photosynthesis, cell growth and stress response, which may lead to the imbalance of redox homeostasis and cell damage. Taken together, sufficient levels of β-ionone and β-cyclocitral can act as growth inhibitors suppressing the growth of Dunaliella cells.