ABSTRACT
Particular strains of Dunaliella salina, D. bardawil and Haematococcus pluvialis (Chlorophyta) transform from green to red cells under extreme environmental conditions, such as high light intensity, high salinity, low nutrients and extremes of temperature. Massive quantities of either β,β-carotene (Dunaliella) or astaxanthin (Haematococcus) may be synthesized under these conditions, which are thought to be photoprotective responses to the photoinhibition induced. Commercial harvesting of these pigments (β,β-carotene and astaxanthin), which are both valuable food colouring agents in marine animal culture world-wide, mean that optimal conditions for successful production of these carotenoids in the farming situation are continually sought.
This brief review begins with new concepts on the origins of algal chloroplasts, then high-lights some key aspects of the biochemistry of pigments – chlorophylls and carotenoids – in the Chlorophyta. Particular attention is given to the role of stereoisomers in the functioning of the photosynthetic apparatus. Several methods of pigment analysis useful for monitoring the development of carotenogenesis in the farming situation are described, including methods for the HPLC analysis of Dunaliella and Haematococcus pigments. Pathways for chlorophyll and carotenoid biosynthesis in the Chlorophyta are discussed, noting that more information on gene regulation and enzyme transcription processes is needed. Finally, the biochemistry and ecology of the red-pigmented forms of Dunaliella and Haematococcus are compared.
