13C‐NMR spectroscopy as a tool to study organic osmolytes in the mangrove red algal genera Bostrychia and Stictosiphonia (Ceramiales)

SUMMARY Field and culture samples of the red algal genera Bostrychia and Stictosiphonia from all around the world were analyzed for the polyols D‐sorbitol and dulcitol, that function as osmolytes, as well as for the heteroside digeneaside by using 13C‐NMR spectroscopy and HPLC. While all plants exhibited D‐sorbitol, the occurrence of dulcitol and digeneaside was highly variable. Therefore, different types of low molecular weight carbohydrate distribution patterns were found in Bostrychia and Stictosiphonia. The presence of D‐sorbitol seems to be a reliable chemosystematic character for both genera, because no other red alga is known to contain this compound. The lack of dulcitol may be correlated with the geographical origin of the Bostrychia and Stictosiphonia samples: while all tropical isolates exhibited both sugar alcohols, in cold‐temperate plants only D‐sorbitol was determined. In warm‐temperate species, however, both polyol distribution types may occur. These data are discussed in terms of possible temperature sensitivity of the dulcitol pathway. However, the biological function of digeneaside (the main photo‐assimilated compound in members of the order Ceramiales) is still obscure.