Light regulation of assimilatory sulphate reduction in Arabidopsis thaliana

• Published in: The Plant journal : for cell and molecular biology 1999-10, Vol.20 (1), p.37-44
• Main Authors: Kopriva, S, Muheim, R, Koprivova, A, Trachsel, N, Catalano, C, Suter, M, Brunold, C
• Format: Article
• Language: English
• Subjects: adenosine phosphates; adenylyl-sulfate reductase; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - radiation effects; Arabidopsis thaliana; Biological and medical sciences; chemical constituents of plants; Circadian Rhythm; culture media; dark; Darkness; diurnal variation; enzyme activity; Fundamental and applied biological sciences. Psychology; gene expression; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Plant - drug effects; Genes, Plant; genetic regulation; Isoenzymes - genetics; Isoenzymes - metabolism; isotope labeling; isozymes; Light; messenger RNA; Metabolism; Metabolism. Physicochemical requirements; nutrient uptake; Oxidation-Reduction; oxidoreductases; Oxidoreductases - genetics; Oxidoreductases - metabolism; Oxidoreductases Acting on Sulfur Group Donors; Plant physiology and development; Plant Roots - metabolism; Plant Shoots - metabolism; reduction; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Plant - genetics; RNA, Plant - metabolism; roots; shoots; Space life sciences; sucrose; Sucrose - pharmacology; sulfates; Sulfates - metabolism
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1046/j.1365-313X.1999.00573.x

Adenosine 5'-phosphosulphate reductase (APR) is considered to be a key enzyme of sulphate assimilation in higher plants. We analysed the diurnal fluctuations of total APR activity and protein accumulation together with the mRNA levels of three APR isoforms of Arabidopsis thaliana. The APR activity reached maximum values 4 h after light onset in both shoots and roots; the minimum activity was detected at the beginning of the night. During prolonged light, the activity remained stable and low in shoots, but followed the normal rhythm in roots. On the other hand, the activity decreased rapidly to undetectable levels within 24 h of prolonged darkness both in shoots and roots. Subsequent re-illumination restored the activity to 50% in shoots and to 20% in roots within 8 h. The mRNA levels of all three APR isoforms showed a diurnal rhythm, with a maximum at 2 h after light onset. The variation of APR2 mRNA was more prominent compared to APR1 and APR3. (35)SO4(2-) feeding experiments showed that the incorporation of (35)S into reduced sulphur compounds in vivo was significantly higher in light than in the dark. A strong increase of mRNA and protein accumulation as well as enzyme activity during the last 4 h of the dark period was observed, implying that light was not the only factor involved in APR regulation. Indeed, addition of 0.5% sucrose to the nutrient solution after 38 h of darkness led to a sevenfold increase of root APR activity over 6 h. We therefore conclude that changes in sugar concentrations are also involved in APR regulation.