MONO‐ AND DIGALACTOSYLDIACYLGLYCEROL COMPOSITION OF RAPHIDOPHYTES (RAPHIDOPHYCEAE): A MODERN INTERPRETATION USING POSITIVE‐ION ELECTROSPRAY/MASS SPECTROMETRY/MASS SPECTROMETRY¹

Abstract

Raphidophyte algae (Raphidophyceae) can be divided according to pigment composition and plastid ancestry into two categories, brown- and green-pigmented taxa. We sought to examine if there are any biochemical differences in plastid lipid composition between the two groups. To this end, the composition and positional distribution of fatty acids of the chloroplast lipids, mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), were examined using positive-ion electrospray/mass spectrometry (ESI/MS) and electrospray/mass spectrometry/mass spectrometry (ESI/MS/MS). Brown-pigmented strains from the genera Chattonella, Fibrocapsa, and Heterosigma primarily consisted of 20:5/18:4 (sn-1/sn-2) MGDG and 20:5/18:4 DGDG, while isolates of the green-pigmented raphidophyte Gonyostomum semen (Ehrenb.) Diesing contained these as well as 18:3/18:4 MGDG and DGDG, thus underscoring its green algal plastid lineage. Although previously unseen without the regiochemical information provided by ESI/MS/MS, Chattonella subsalsa Biecheler possessed 20:5/18:3 DGDG as a major form, a potential biosynthetic intermediate in the production of 20:5/18:4 DGDG. These results provide a modern interpretation of the fatty acid regiochemistry of MGDG and DGDG.

Pigment composition and photoacclimation as keys to the ecological success of Gonyostomum semen (Raphidophyceae, Stramenopiles)

“…This species might have acquired the pigment allo by tertiary endosymbiosis of a cryptophyte, which would represent different evolutionary plastid acquisition in marine taxa, like Chattonella , Fibrocapsa and Heterosigma , than in freshwater raphidophytes. This hypothesis is supported by differences in fatty acid and sterol composition between brown‐pigmented, marine raphidophytes and green‐pigmented species ( Gonyostomum and Vacuolaria ; Roche and Leblond , Leblond et al. ).…”

Algal lipids, fatty acids and sterols

“…Leblond and co-workers extensively studied the glycolipid profi les of dinofl agellate Pyrocystis spp., glaucocystophytes Cyanophora paradoxa and Glaucocystis nostochinearum , raphidophytes Chattonella , Fibrocapsa and Heterosigma spp. and chlororachinophytes Bigelowiella natans , Gymnochlora stellata and Lotharella spp., with the latter chlororachinophytic algae exhibiting a novel lauric acid containing MGDG (C20:5/C12:0, sn -1/ sn -2) (Leblond and Roche, 2009;Leblond et al , 2010a;Leblond et al , 2010b;Roche and Leblond, 2011). Wu et al .…”

Sterols of the Green‐Pigmented, Freshwater Raphidophyte, Gonyostomum semen, from Scandinavian Lakes

“…The strains were grown in duplicate under the same conditions as the earlier study on raphidophyte chloroplast galactolipids by Roche and Leblond (). Briefly, the isolates were grown in MWC medium with an addition of selenium at 20 °C, an irradiance of approximately 50 μE/m 2 /s, and a day: night cycle of 14:10‐h, and harvested and extracted according to the methodology of Leblond and Chapman (), which is based on a modified Bligh and Dyer extraction (Guckert et al.…”

“…). Recently, brown‐ and green‐pigmented raphidophytes have been found also to differ in the fatty acid composition of the chloroplast‐associated galactolipids, mono‐ and di‐galactosyldiacylglycerol (Roche and Leblond ). These pigment and galactolipid differences between the brown‐ and green‐pigmented taxa may be biochemical indicators of different chloroplast ancestries; brown‐pigmented raphidophytes are considered to have obtained their chloroplast from a red algal ancestor (Cavalier‐Smith ), whereas green‐pigmented raphidophytes have most likely obtained their chloroplast from a green algal ancestor, although, to our knowledge, molecular genetic studies to this effect have not been carried out yet.…”