INHIBITION OF ASTAXANTHIN SYNTHESIS UNDER HIGH IRRADIANCE DOES NOT ABOLISH TRIACYLGLYCEROL ACCUMULATION IN THE GREEN ALGA HAEMATOCOCCUS PLUVIALIS (CHLOROPHYCEAE)¹

Abstract

Under stress conditions, Haematococcus pluvialisFlotow accumulates fatty acid-esterified astaxanthin, in extraplastidial lipid globules. The enhanced accumulation of fatty acids, mainly in triacylglycerols (TAG), among which oleic acid predominates, is linearly correlated with that of astaxanthin. We used inhibitors of either carotenoid or lipid biosynthesis to assess the interrelationship between carotenogenesis and TAG accumulation under high light irradiance as the stress factor. The two carotenogenesis inhibitors usednorflurazon, an inhibitor of phytoene desaturase, and diphenylamine (DPA), an inhibitor of b-carotene C-4 oxygenase-suppressed the accumulation of astaxanthin in a concentration-dependent manner. Concurrently, the accumulation of neutral lipids was significantly less affected. The lipid biosynthesis inhibitor sethoxydim, which inhibits acetyl-CoA carboxylase, significantly decreased de novo fatty acid synthesis and, in concert, drastically inhibited astaxanthin formation. In the presence of various concentrations of the three inhibitors, the inhibition of astaxanthin was not accompanied by a proportional decrease in oleic acid, which was used as a marker for TAG fatty acids. When astaxanthin synthesis was completely inhibited, the volumetric content of oleic acid was about 60% of the control value when the two carotenogenesis inhibitors (0.05 lM norflurazon or 20 lM DPA) were used and 27% of the control when the lipid-synthesis inhibitor (50 lM) was used. We suggest therefore that TAG accumulation under high irradiance is not tightly coupled with astaxanthin accumulation, although the correlation between these two processes was demonstrated earlier. Furthermore, we propose that the accumulation of a certain amount of TAG is a prerequisite for the initiation of fatty acid-esterified astaxanthin accumulation in lipid globules.

Metabolite Profiling and Integrative Modeling Reveal Metabolic Constraints for Carbon Partitioning under Nitrogen Starvation in the Green Algae Haematococcus pluvialis

“…However, FA accumulation is not dependent on astaxanthin synthesis (33), and as also shown for different algae (57), FA accumulation represents a more general stress response. Although some data on CH content under stress conditions can be found (6), only recently (12) was the dynamics of CH accumulation/degradation under stress targeted.…”

“…Algal Cultures-H. pluvialis was cultured as described previously (33). Cultures of green (non-flagellated) cells were first cultivated for 5 days in mBG-11 medium at an irradiance of 75 E m Ϫ2 s Ϫ1 .…”

Characterization of Dunaliella salina strains by flow cytometry: a new approach to select carotenoid hyperproducing strains

“…Previous works showed the possibility of using this dye as an indicator of the lipidic and fatty acid composition in some species using flow cytometry (de la Jara et al 2003). In D. salina and in other alga, as Haematococcus sp, both the fatty acid profile and lipid composition are closely related to the massive carotenoids accumulation (Rabbani et al 1998;Grünewald et al 2001;Zhekisheva et al 2005) in such a way that it is possible to establish a link between them (Mendoza et al 1999). Our results show that changes in the D. salina lipidic composition associated with the carotenogenetic process could be detected by flow cytometry using NR, a lipidic fluorescent marker that enabled us to estimate the carotene cellular content despite the low fluorescence of carotenoids.…”

Enhanced protection against oxidative stress in an astaxanthin-overproductionHaematococcusmutant (Chlorophyceae)

“…Application of inhibitors to certain enzymes involved in carotenogenesis represents another common approach to depict the possible role of astaxanthin in stress response and also assist in identifying genuine intermediates in the pathway of astaxanthin biosynthesis (Fan et al, 1995(Fan et al, , 1998Harker & Young, 1995;Zhekisheva et al, 2005). The increase in susceptibility or cell mortality of inhibitor-treated algal cells to high light and/or other environmental stimuli was used as evidence to support the photoprotective role of astaxanthin in untreated ones.…”

“…The increase in susceptibility or cell mortality of inhibitor-treated algal cells to high light and/or other environmental stimuli was used as evidence to support the photoprotective role of astaxanthin in untreated ones. However, the proven toxic side-effect and/or limited inhibition-specificity of these tested inhibitors made the above observation less conclusive (Sandmann & Boger, 1989;Fan et al, 1995;Harker & Young, 1995;Zhekisheva et al, 2005).…”