Synthesis and properties of glutathione reductase in stressed peas

Abstract

We have subjected peas (Pisum sativum L.) to four different oxidative stresses: cold conditions (4 °C) in conjunction with light, treatment with paraquat, fumigation with ozone, and illumination of etiolated seedlings (greening). In crude extracts of leaves from stressed plants, an increase (up to twofold) in activity of glutathione reductase (GR) was observed which was consistent with previous reports from several laboratories. In all cases, except for ozone fumigation, the increase in activity was not due to an elevation in the steady-state levels of GR protein. None of the applied stresses had any effect on steady-state levels of GR mRNA. In contrast to the small increase in GR activity, the K m of GR for glutathione disulphide showed a marked decrease when determined for extracts of stressed leaves, compared with that from unstressed plants. This indicates that GR from stressed plants has an increased affinity for glutathione disulphide. The profile of GR activity bands fractionated on non-denaturing acrylamide gels varied for extracts from differently stressed leaves and when compared with GR from unstressed plants. The changes in GR-band profiles and the alteration in the kinetic properties are best explained as changes in the isoform population of pea GR in response to stress.