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

After a 7-day preconditioning in the dark in filtered seawater, excised fra gments of Solieria chordalis were pooled before being distributed in cultur e tanks at three salinity conditions (22, 34, and 52 parts per thousand). A lgae cuts were taken from each tank at various incubation times to measure NDP-sugar pool size, floridoside, starch, and carrageenan yield, and UDP-gl ucose-pyrophosphorylase and -epimerase activities. Floridean starch content was unaffected in the thalli of Solieria chordalis cultivated in altered s alinity, i.e. 22 or 52 parts per thousand, as compared to those maintained in normal salinity (34 parts per thousand). In contrast, a brief increase i n floridoside content was observed in the thalli cultivated in hypersalinit y medium. This increase was fast, and after 24h the level of floridoside in the algae came back to the reference value. Carrageenan contents were lowe r in altered salinity than in the reference. Moreover, the ratio of 3,6-anh ydrogalactose to carrageenan increased at salinity 22 and 52 parts per thou sand as compared to the reference. This indicated a modification of carrage enan composition with osmotic stress. No significant variation in UDP-gluco se 4-epimerase was found in the three salinities studied. In contrast, UDP- glucose pyrophosphorylase activity was inhibited at high and low salinity d uring the first two days of culture. This enzyme seems to play a key-role i n the flow of NDP-sugars in red alga metabolism.