L-Ascorbic-acid biosynthesis in the euryhaline diatom Cyclotella cryptica.

L-Ascorbic acid (AA) production in cells of Cyclotella cryptica Reimann, Lewin, Guillard (Bacillariophyceae) is enhanced when darkadapted cells are exposed to light.Heterotrophically grown cells incubated with D-[6-(3)H,6-(14)C]glucose and D-[1-(3)H,6-(14)C]glucose (2 h in dark followed by 15 h light) produced labeled AA with significantly different ratios of (3)H and (14)C. Comparisons of labeling patterns in AA and chitin-derived D-glucosamine support a path of conversion in Cyclotella from D-glucose to AA that "inverts" the carbon chain of the sugar. This process resembles similar conversions found in AA-synthesizing animals and species from two other algal classes.