, Volume 198, Issue 1, pp 151-157

Differential redox regulation by glutathione of glutathione reductase and CuZn-superoxide dismutase gene expression in Pinus sylvestris L. needles

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Abstract

Glutathione reductase (GR; EC 1.6.4.2) and superoxide dismutase (SOD; EC 1.15.1.1) are two well-known enzymes involved in the scavenging of reactive oxygen intermediates. However, little is known about the regulation of Gor and Sod genes in plant cells. To obtain information about hypothetical redox regulatory mechanisms controlling Gor and Sod gene expression we artificially enhanced the levels of reduced and oxidized forms of glutathione (GSH and GSSG) in Pinus sylvestris L. needles. Scots pine shoots were placed for 12 h in beakers containing 5 mM GSH, 5 mM GSSG or water. Increased levels of both GSSG and GSH were observed in the GSSG-treated needles after 3 h. In contrast, only the GSH level was increased by the GSH treatment. Thus, the GSH/GSSG ratio increased up to 15-fold during the GSH treatment and decreased approximately two-fold during the GSSG treatment. The GR activity was significantly higher (60%) when GSSG was applied, without any apparent change in the amount and isoform population of GR or accumulation of Gor gene transcripts. This indicates that the GR activity increased per se in the GSSG treatment. The level of cytosolic CuZn-Sod transcripts was decreased significantly by the GSH treatment without any change in enzyme activity. The chloroplastic CuZnSod gene generally showed a more stable transcript level in the different treatments. However, a similarity between the cytosolic and chloroplastic levels of CuZn-Sod transcripts could be observed in different treatments. This suggests that the redox state of glutathione plays an important role in the in vivo regulation of CuZn-Sod gene expression in plants.

We are grateful to Dr. Gary P. Creissen (John Innes Institute, Colney Lane, Norwich NR4 7UH, UK) for kindly providing the recombinant plasmid pGR201. Special thanks are offered to Prof. Jan-Erik Hällgren for discussion and critical review of the manuscript, to Dr. Barbara Karpinska for general help and interest and to Margareta Zetherström at our department for excellent technical assistance. This work was supported by the Swedish Council for Forestry and Agricultural Research and The Swedish Council for Natural Research.