Intra-Thallus Variation of Phenolic Compounds and Carbohydrates in Furcellaria lumbricalis (Gigartinales, Rhodophyta) from the White Sea (The Arctic Ocean)

Furcellaria lumbricalis is an industrially important carrageenophyte. However, beyond the carrageenan characterization, the biochemical composition of this alga remains poorly understood. This study provides the first comprehensive description of the metabolome of F. lumbricalis and reveals pronounced biochemical heterogeneity in its thalli by examining the distribution of pigments, phenolic compounds, polysaccharides, and low-molecular-weight metabolites across apical, middle, and basal thallus zones. Understanding the intra-thallus biochemical profiles is necessary for the efficient use of algal feedstock. Untargeted GC-MS analysis of Furcellaria extracts revealed a high diversity of phenolic compounds, accounting for 27% of the annotated metabolome. Meristematic apical cells were enriched in organic acids of the TCA cycle, isofloridoside and various phenolic acids, such as caffeic, protocatechuic, and 3,4-dihydroxyphenylpyruvic, indicating active processes of respiration and secondary metabolism presumably conferring chemical defense. Mature cells of the middle zone accumulated carrageenans and heterosides, supporting structural investment and mobile carbon storage. The basal zone, apparently serving both resource storage and stress tolerance functions, featured a relatively high content of mono- and disaccharides, sugar alcohols, floridean starch, p-coumaric and 3-phenyllactic acids. Overall, these findings establish a metabolic framework for understanding the functional compartmentalization in red macroalgae and provide a foundation for future studies.