title: Exposure to low irradiances favors the synthesis of 9-cis beta, beta-carotene in Dunaliella salina (Teod.).
abstract: We examined the effect of irradiance on the synthesis of beta-carotene and its isomers by Dunaliella salina. Growth irradiance had a marked effect both on growth of the alga (which was suppressed at both low and high irradiances) and on the accumulation of beta-carotene. The accumulation of beta-carotene but not alpha-carotene was closely linked to an increase in irradiance. Growth at low irradiances (20-50 micromol m(-2) s(-1)) promoted a high ratio of 9-cis to all-trans beta-carotene (>2:1), while exposure to high irradiances (200-1,250 micromol m(-2) s(-1)) resulted in a large reduction in this ratio (to <0.45:1). A similar pattern was seen for the geometric isomers of alpha-carotene, with exposure to low irradiance favoring the accumulation of the 9-cis form. The carotenoid biosynthesis inhibitors 4-chloro-5(methylamino)-2-(alpha-alpha-alpha-trifluoro-m-tolyl)-3-(sH )-pyridazinone and 2-(4-chlorophenylthio)triethylamine caused the accumulation of the precursors phytoene and lycopene, respectively, in D. salina. High-performance liquid chromatography and infrared analysis showed that phytoene adopted the 15-cis and all-trans forms (as in higher plants), and that lycopene primarily adopted the all-trans form. This indicates that isomerization of beta-carotene takes place during or after cyclization.
authors.affiliation: Carotenoid Research Group, School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, United Kingdom.
authors.forename: S C
authors.initials: SC
authors.lastname: Orset
authors.forename: A J
authors.initials: AJ
authors.lastname: Young
mesh_terms: D004307:Dose-Response Relationship, Radiation; D056890:Eukaryota / Q000378:metabolism / Q000528:radiation effects*; D008027:Light; D019207:beta Carotene / Q000096:biosynthesis*
chemical_list: D019207:beta Carotene