Nutrient Limitation is the Main Regulatory Factor for Carotenoid Accumulation and for Psy and Pds Steady State Transcript Levels in Dunaliella salina (Chlorophyta) Exposed to High Light and Salt Stress
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Dunaliella salina (Dunal) Teodoresco (1905) is a green unicellular alga able to withstand severe salt, light, and nutrient stress, adaptations necessary to grow in harsh environments such as salt ponds. In response to such growth conditions, this microalga accumulates high amounts of β-carotene in its single chloroplast. In this study, we show that carotenoid accumulation is consistently inhibited in cells grown in nutrient-supplemented media and exposed either to high-light or medium-low-light conditions. Likewise, carotenogenesis in cells shifted to higher salinity (up to 27% NaCl) under medium-low-light conditions is inhibited by the presence of nutrients. The steady-state levels of transcripts encoding phytoene synthase and phytoene desaturase increased substantially in D. salina cells shifted to high light or high salt under nutrient-limiting conditions, whereas the presence of nutrients inhibited this response. The regulatory effect of nutrient availability on the accumulation of carotenoids and messenger RNA levels of the first two enzymes committed to carotenoid biosynthesis is discussed.
KeywordsDunaliella salina Carotenoid biosynthesis Light Nitrate Nutrients Salt Stress
Sacha Coesel, Nuno Henriques, Ana Ramos, and Alexandra Baumgartner were supported by the Portuguese National Budget and Fundação para a Ciência e a Tecnologia, Portugal, with the studentships SFRH/BD/4839/2001, PRAXIS 4/4.1/BD/4267/97, SFRH/BD/13937/2003 and BPD/3579/2000, respectively, and the research grants POCTI/MAR/15237/99 and INTERREG 159-SAL - Atlantic Salt Ponds.
- Ben-Amotz A, Gressel J, Avron A (1987) Massive accumulation of phytoene induced by norflurazon in Dunaliella bardawil (Chlorophyceae) prevents recovery from photoinhibition. J Phycol 23:176–181Google Scholar
- Goodwin TW (1980) The biochemistry of the carotenoids. London, Chapham and HallGoogle Scholar
- Grunewald K, Eckert M, Hirschberg J, Hagen C (2000) Phytoene desaturase is localized exclusively in the chloroplast and up-regulated at the mRNA level during accumulation of secondary carotenoids in Haematococcus pluvialis (Volvocales, Chlorophyceae). Plant Physiol 122:1261–1268PubMedCrossRefGoogle Scholar
- Navalho J (1997) Biotechnology of Dunaliella salina for beta-carotene production. MSc thesis, University of Algarve, Faro, PortugalGoogle Scholar
- Sambrook J, Fritsch EF, Maniatis T (1989) Molecular cloning: a laboratory manual, 2nd ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NYGoogle Scholar
- Simkin AJ, Laboure AM, Kuntz M, Sandmann G (2003a) Comparison of carotenoid content, gene expression and enzyme levels in tomato (Lycopersicon esculentum) leaves. Z Naturforsch [C] 58:371–380Google Scholar
- Von Lintig J, Welsch R, Bonk M, Giuliano G, Batschauer A, Kleinig H (1997) Light-dependent regulation of carotenoid biosynthesis occurs at the level of phytoene synthase expression and is mediated by phytochrome in Sinapis alba and Arabidopsis thaliana seedlings. Plant J 12:625–634CrossRefGoogle Scholar