Light regulation of carotenoid biosynthesis in the prasinophycean alga Mantoniella squamata

  • Böhme K
  • Wilhelm C
  • Goss R
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Abstract

We have studied carotenoid biosynthesis in the prasinophycean alga Mantoniella squamata, which contains a great variety of carotenoids belonging to both the α- and the β-carotene (Car) biosyntheses pathways. This unusual carotenoid composition allowed us to address the problem of how biosynthesis on the α- and the β-Car pathway is regulated in response to different light regimes. We found that illumination with 4 h of actinic high light (HL, 250 µmol m?2 s?1 ), and culture growth in permanent light (PL, 60 µmol m?2 s?1 ), induced the de novo synthesis of violaxanthin (Vx) cycle pigments belonging to the β-Car pathway. Carotenoid synthesis on the α-Car biosynthesis pathway led to a strong accumulation of lutein (L) and dihydrolutein (DhL). Both the newly synthesised Vx cycle pigments and L/DhL can be regarded as intermediate pools of carotenoids that were converted to light-harvesting pigments in low light (LL) periods following the phases of HL illumination. This transition to the light-harvesting pigments included the conversion of Vx to neoxanthin (Nx) on the β-Car pathway, and the transformation of L/DhL to prasinoxanthin (Px), the main light-harvesting pigment of M. squamata belonging to the α-carotenoids. Isolation of light-harvesting complexes from L-enriched M. squamata cells showed that both L and the Vx cycle pigments were loosely bound to the LHC apoprotein. This peripheral binding is in agreement with their proposed role as intermediate pigments in the biosynthesis of light-harvesting pigments, and should allow a smooth detachment from the protein in periods of LL when the synthesis of Nx and Px is stimulated. We conclude that carotenoid synthesis proceeds in general in an economical way: in both, the α- and the β-Car pathway HL induces the formation of photoprotective pigments, which in LL periods following the HL illumination are not degraded, but on the contrary are converted to light-harvesting pigments. Introduction

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Authors

  • Karen Böhme

  • Christian Wilhelm

  • Reimund Goss

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