Salinity effects on NDP-sugars, floridoside, starch, and carrageenan yield, and UDP-glucose-pyrophosphorylase and -epimerase activities of cultivated Solieria chordalis

After a 7-day preconditioning in the dark in filtered seawater, excised fragments of Solieria chordalis were pooled before being distributed in culture tanks at three salinity conditions (22, 34, and 52 ‰). Algae cuts were taken from each tank at various incubation times to measure NDP-sugar pool size, floridoside, starch, and carrageenan yield, and UDP-glucose-pyrophosphorylase and -epimerase activities. Floridean starch content was unaffected in the thalli of Solieria chordalis cultivated in altered salinity, i.e. 22 or 52 ‰, as compared to those maintained in normal salinity (34 ‰). In contrast, a brief increase in floridoside content was observed in the thalli cultivated in hypersalinity medium. This increase was fast, and after 24 h the level of floridoside in the algae came back to the reference value. Carrageenan contents were lower in altered salinity than in the reference. Moreover, the ratio of 3,6-anhydrogalactose to carrageenan increased at salinity 22 and 52 ‰ as compared to the reference. This indicated a modification of carrageenan composition with osmotic stress. No significant variation in UDP-glucose 4-epimerase was found in the three salinities studied. In contrast, UDP-glucose pyrophosphorylase activity was inhibited at high and low salinity during the first two days of culture. This enzyme seems to play a key-role in the flow of NDP-sugars in red alga metabolism.