Responses to cadmium in leaves of transformed poplars overexpressing gamma-glutamylcysteine synthetase

Poplars overexpressing a bacterial gamma-glutamylcysteine synthetase (gamma -ECS) in the cytosol (lines ggs11 and ggs28) had a 30-fold increase in foli ar gamma-ECS activity relative to untransformed controls. Foliar gamma-glut amylcysteine (gamma-EC) was increased by 10-fold while foliar glutathione a ccumulation increased by up to 3.5-fold in the leaves of the transformants, Untransformed and transformed poplars were grown with different soil conce ntrations of cadmium (0-1100 mu g g(-1) soil) for 2 weeks. Cadmium accumula ted in the leaves of both transformed and untransformed poplars and growth was inhibited. Growth inhibition and foliar cadmium accumulation were great est at the highest soil cadmium concentrations in all lines. Exposure to ca dmium enhanced the foliar cysteine, gamma-EC and glutathione pools in all l ines but less glutathione was present in the leaves of the untransformed co ntrols than the transformants under all growth conditions. Cadmium-induced changes in the activities of malic enzyme, isocitrate dehydrogenase and gua iacol peroxidase were less pronounced in the leaves of the transformed popl ars overexpressing gamma-ECS than in the untransformed controls. Glutamate dehydrogenase and glutathione reductase activities were unchanged by exposu re to cadmium. We conclude that overexpression of gamma-ECS activity and fo liar glutathione accumulation in transformed poplar allows greater tissue c admium accumulation but has only a marginal effect on cadmium tolerance in poplar.