and that this exceptional stress response is mediated by The unicellular green alga Haematococcus plu7ialis Flotow has recently aroused considerable interest due to its capacity reactive oxygen species (ROS) through a mechanism which is not yet understood. The results do not support in vivo chemi-to amass large amounts of the ketocarotenoid astaxanthin (3,3%-dihydroxy-,-carotene-4,4%-dione), widely used com-cal quenching of ROS by the pigment, although in vitro it was shown to quench radicals very efficiently. The finding that mercially to color flesh of salmon. Astaxanthin accumulation in Haematococcus is induced by a variety of environmental most of the pigment produced is esterified and deposited in lipid globules outside the chloroplast further supports this stresses which limit cell growth in the presence of light. This is accompanied by a remarkable morphological and biochemi-assumption. We have suggested that astaxanthin is the byproduct of a defense mechanism rather than the defending cal 'transformation' from green motile cells into inert red cysts. In recent years we have studied this transformation substance itself, although at this stage one cannot rule out process from several aspects: defining conditions governing other protective mechanisms. Further work is required for complete understanding of this transformation process. It is pigment accumulation, working out the biosynthetic pathway suggested that Haematococcus may serve as a simple model of astaxanthin accumulation and questioning the possible function of this secondary ketocarotenoid in protecting system to study response to oxidative stress and mechanisms Haematococcus cells against oxidative damage. Our results evolved to cope with this harmful situation. suggest that astaxanthin synthesis proceeds via cantaxanthin astaxanthin can be synthesized by plants, bacteria, a few fungi , Johnson and Schroeder 1996, Tsubokura et al. 1999) and green algae (Fjerdingstad et al. 1974), the amounts accumulated by the green alga Haematococcus plu6ialis ) surpass any other reported source. Thus, the research on H. plu6ialis has been accelerated by the hope that it may become an important natural source for the mass production of astaxanthin. In this study, aspects concerning growth, physiology and the carotenogenesis process will be discussed. The interrelationships between reactive oxygen species (ROS) and astaxanthin in the stress response and photoprotection will be reviewed.Abbre6iations -DPA, diphenylamine; PSI (II), photosystem I (II); ROS, reactive oxygen species; SOD, superoxide dismutase.

We examined responses of batch cultures of the marine microalga Nannochloropsis sp. to combined alterations in salinity (13, 27, and 40 g/l NaCl) and light intensity (170 and 700 μmol photons/m(2)·s). Major growth parameters and lipid productivity (based on total fatty acid determination) were determined in nitrogen-replete and nitrogen-depleted cultures of an initial biomass of 0.8 and 1.4 g/l, respectively. On the nitrogen-replete medium, increases in light intensity and salinity increased the cellular content of dry weight and lipids due to enhanced formation of triacylglycerols (TAG). Maximum average productivity of ca. 410 mg TFA/l/d were obtained at 700 μmol photons/m(2)·s and 40 g/l NaCl within 7 days. Under stressful conditions, content of the major LC-PUFA, eicosapentaenoic acid (EPA), was significantly reduced while TAG reached 25% of biomass. In contrast, lower salinity tended to improve major growth parameters, consistent with less variation in EPA contents. Combined higher salinity and light intensity was detrimental to lipid productivity under nitrogen starvation; biomass TFA content, and lipid productivity amounted for only 33% of DW and ca. 200 mg TFA/l/day, respectively. The highest biomass TFA content (ca. 47% DW) and average lipid productivity of ca. 360 mg TFA/l/day were achieved at 13 g/l NaCl and 700 μmol photons/m(2)·s. Our data further support selecting Nannochloropsis as promising microalgae for biodiesel production. Moreover, appropriate cultivation regimes may render Nannochloropsis microalgae to produce simultaneously major valuable components, EPA, and TAG, while sustaining relatively high biomass growth rates.

No abstract

Cells of the green microalga Haematococcus pluvialis were induced to accumulate the ketocarotenoid pigment, astaxanthin. This induction was achieved by the application of the following environmental conditions: light intensity (170//mol m~2s~'), phosphate starvation and salt stress (NaCl 0.8%). These conditions retarded cell growth as reflected by a decrease in cell division rate, but led to an increase in astaxanthin content per cell. Accumulation of astaxanthin required nitrogen and was associated with a change in the cell stage from biflagellate vegetative green cells to non-motile and large resting cells. It is suggested that environmental or nutritional stresses, which interfere with cell division, trigger the accumulation of astaxanthin. Indeed, when a specific inhibitor of cell division was applied, a massive accumulation of astaxanthin occurred.

The chlorophyte Haematococcus pluvialis accumulates large quantities of astaxanthin under stress conditions. Under either nitrogen starvation or high light, the production of each picogram of astaxanthin was accompanied by that of 5 or 3–4 pg of fatty acids, respectively. In both cases, the newly formed fatty acids, consisting mostly of oleic (up to 34% of fatty acids in comparison with 13% in the control), palmitic, and linoleic acids, were deposited mostly in triacylglycerols. Furthermore, the enhanced accumulation of oleic acid was linearily correlated with that of astaxanthin. Astaxanthin, which is mostly monoesterified, is deposited in globules made of triacylglycerols. We suggest that the production of oleic acid‐rich triacylglycerols on the one hand and the esterification of astaxanthin on the other hand enable the oil globules to maintain the high content of astaxanthin esters.