Differential redox regulation by glutathione of glutathione reductase and CuZn-superoxide dismutase gene expression inPinus sylvestrisL. needles

摘要

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 ofGorandSodgenes in plant cells. To obtain information about hypothetical redox regulatory mechanisms controllingGorandSodgene expression we artificially enhanced the levels of reduced and oxidized forms of glutathione (GSH and GSSG) inPinus sylvestrisL. 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 ofGorgene transcripts. This indicates that the GR activity increased per se in the GSSG treatment. The level of cytosolic CuZn-Sodtranscripts was decreased significantly by the GSH treatment without any change in enzyme activity. The chloroplastic CuZnSodgene generally showed a more stable transcript level in the different treatments. However, a similarity between the cytosolic and chloroplastic levels of CuZn-Sodtranscripts 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-Sodgene expression in plants.