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.
