title: Selective inhibition of HEMA gene expression by photooxidation in Arabidopsis thaliana.
abstract: Norflurazon (NF), a photobleaching herbicide, inhibits carotenoid biosynthesis. Lack of carotenoid pigments leads to photooxidative damage of chloroplasts. In this study of Arabidopsis thaliana we demonstrate that NF-treated photobleached plants are still able to make 5-aminolevulinic acid (ALA) the first precursor of porphyrins and tetrapyrroles. ALA is formed in the tRNA-dependent two-step C5-pathway in the chloroplast of plants. The expression of glutamyl-tRNA reductase (GluTR), the first enzyme in the pathway, was severely inhibited by NF, while treatment with this compound did not significantly reduce the levels of the other enzyme, glutamate-l-semialdehyde aminomutase, or of tRNA(Glu), the initial metabolite of the pathway. Extracts of these plants retained the capacity, albeit reduced, to convert exogenously added glutamate to ALA. Thus, the much-reduced level of ALA formation in photobleached plants is due to selective inhibition of GluTR expression.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Kumar
authors.forename: S
authors.initials: S
authors.lastname: Chaturvedi
authors.forename: D
authors.initials: D
authors.lastname: Söll
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D000622:Aminolevulinic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects*; D018698:Glutamic Acid / Q000378:metabolism; D010084:Oxidation-Reduction; D010777:Photochemistry
chemical_list: D018698:Glutamic Acid; D000622:Aminolevulinic Acid; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase