Red Light Control of β-Carotene Isomerisation to <i>9</i>-cis β-Carotene and Carotenoid Accumulation in <i>Dunaliella salina</i>
oleh: Yanan Xu, Patricia J. Harvey
| Format: | Article |
|---|---|
| Diterbitkan: | MDPI AG 2019-05-01 |
Deskripsi
<i>Dunaliella salina</i> is a rich source of <i>9-cis</i> β-carotene, which has been identified as an important biomolecule in the treatment of retinal dystrophies and other diseases. We previously showed that chlorophyll absorption of red light photons in <i>D. salina</i> is coupled with oxygen reduction and phytoene desaturation, and that it increases the pool size of β-carotene. Here, we show for the first time that growth under red light also controls the conversion of extant <i>all-trans</i> β-carotene to <i>9-cis</i> β-carotene by β-carotene isomerases. Cells illuminated with red light from a light emitting diode (LED) during cultivation contained a higher <i>9-cis</i> β-carotene content compared to cells illuminated with white or blue LED light. The <i>9-cis</i>/<i>all-trans</i> β-carotene ratio in red light treated cultures reached >2.5 within 48 h, and was independent of light intensity. Illumination using red light filters that eliminated blue wavelength light also increased the <i>9-cis</i>/<i>all-trans</i> β-carotene ratio. With norflurazon, a phytoene desaturase inhibitor which blocked downstream biosynthesis of β-carotene, extant <i>all-trans</i> β-carotene was converted to <i>9-cis</i> β-carotene during growth with red light and the <i>9-cis</i>/<i>all-trans</i> β-carotene ratio was ~2. With blue light under the same conditions, <i>9-cis</i> β-carotene was likely destroyed at a greater rate than <i>all-trans</i> β-carotene (<i>9-cis</i>/<i>all-trans</i> ratio 0.5). Red light perception by the red light photoreceptor, phytochrome, may increase the pool size of anti-oxidant, specifically <i>9-cis</i> β-carotene, both by upregulating phytoene synthase to increase the rate of biosynthesis of β-carotene and to reduce the rate of formation of reactive oxygen species (ROS), and by upregulating β-carotene isomerases to convert extant <i>all-trans</i> β-carotene to <i>9-cis</i> β-carotene.