Naoko Asai

Light-controlled expression of a gene encoding l-galactono-γ-lactone dehydrogenase which affects ascorbate pool size in Arabidopsis thaliana☆

Abstract The cDNA clones for l -galactono-γ-lactone dehydrogenase (EC 1.3.2.3; GLDHase) that catalyzes the final step in the ascorbic acid (AsA) synthetic pathway, were isolated from Arabidopsis thaliana. The gene (AtGLDH) encodes a polypeptide of 610 amino acids and the predicted amino acid sequence was highly homologous to GLDHases from other plant species. The AtGLDH mRNA level of seedlings exhibited a diurnal change; the level was low in the morning and increased during the day. Its level in the evening (at 18:00) was about 2-fold that in the morning (at 6:00). Then the level decreased during the night until dawn of the next day. Similar diurnal changes were also observed in GLDHase activity and AsA content, suggesting that the AsA pool size is, at least partly, determined by the transcription rate of AtGLDH. Moreover, the diurnal changes of mRNA level, enzyme activity, and AsA content were not observed if plants were kept in continuous darkness. These results suggest that the diurnal change in expression of AtGLDH, which may play an important role in the regulation of AsA pool size, is regulated not by a circadian rhythm but by light.