Abstract
The halotolerant photoautotrophic marine microalga Dunaliella salina is one of the richest sources of natural carotenoids. Here we investigated the effects of high intensity blue, red and white light from light emitting diodes (LED) on the production of carotenoids by strains of D. salina under nutrient sufficiency and strict temperature control favouring growth. Growth in high intensity red light was associated with carotenoid accumulation and a high rate of oxygen uptake. On transfer to blue light, a massive drop in carotenoid content was recorded along with very high rates of photo-oxidation. In high intensity blue light, growth was maintained at the same rate as in red or white light, but without carotenoid accumulation; transfer to red light stimulated a small increase in carotenoid content. The data support chlorophyll absorption of red light photons to reduce plastoquinone in photosystem II, coupled to phytoene desaturation by plastoquinol:oxygen oxidoreductase, with oxygen as electron acceptor. Partitioning of electrons between photosynthesis and carotenoid biosynthesis would depend on both red photon flux intensity and phytoene synthase upregulation by the red light photoreceptor, phytochrome. Red light control of carotenoid biosynthesis and accumulation reduces the rate of formation of reactive oxygen species (ROS) as well as increases the pool size of anti-oxidant.
Highlights
Carotenoids are orange, yellow or red pigments which are synthesized by all photosynthetic organisms for light-harvesting and for photo-protection, and for stabilising the pigment–protein light-harvesting complexes and photosynthetic reaction centres in the thylakoid membrane
The initial phase of growth in all high intensity light conditions, apart from blue, caused an initial sharp drop in chlorophyll content; the drop was greatest in high intensity red light emitting diodes (LED) light but decreased depending on the relative proportions of red: blue light supplied
Carotenoids in D. salina Collection of Algae and Protozoa (CCAP) 19/41 cultures exposed to different light conditions: white, red or blue LED light at 1000 μmol photons m−2 s−1, a mixture of white and red (1:1) or a mixture of white and blue (1:1) with a total intensity of 1000 μmol photons m−2 s−1 for 48 h were extracted and the major carotenoids were identified and quantified by HPLC
Summary
Carotenoids are orange, yellow or red pigments which are synthesized by all photosynthetic organisms for light-harvesting and for photo-protection, and for stabilising the pigment–protein light-harvesting complexes and photosynthetic reaction centres in the thylakoid membrane. Sought after as natural colorants, there is accumulating evidence that carotenoids protect humans against ageing and diseases that are caused by harmful free radicals and may reduce the risks of cataract, macular degeneration, neurodegeneration and some cancers [5,6]. They have been implicated as the actives for treating diseases associated with retinoids [4].
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