Measuring low-molecular-weight thiols by detecting the fluorescence of their SBD-derivatives: application to studies of diurnal and UV-B induced changes in Zea mays L.

The composition of low-molecular-weight thiols in Zea mays L. was investigated by HPLC separation following derivatisation with SBD-F (ammonium 7-fluoro 2,1,3-benzooxadiazole-4-sulfonate) as a fluorescent label. This method was applied to describing variations in the acid-soluble thiol pool in a normal dark/light cycle, and with supplemental UV-B radiation causing moderate photo-oxidative stress. We provide evidence of an increase in leaf η-glu-cys content during the night. This finding suggests that η-glu-cys accumulation in the absence of light is a general phenomenon, though it is not yet clear whether glycine availability from photorespiration is the underlying mechanism in C4 plants too. UV-B radiation caused a significant increase in η-glu-cys content in both shoots and roots. A faster loss of GSH in shoots, in experiments where the glutathione biosynthesis inhibitor buthionine sulfoximine was used, indicates that UV-B radiation enhances glutathione degradation. This is consistent with a higher content of cys-gly (reported to be a η-glutamyl-transpeptidase degradation product of glutathione or its conjugates) in shoots of UV-B exposed seedlings.