Overexpression of -Glutamylcysteine Synthetase, but not of Glutathione Synthetase, Elevates Glutathione Allocation in the Phloem of Transgenic Poplar Trees

Phloem exudates were collected along the tree axis at different heights of wild type and transgenic poplar. Over-expression of bacterial γ-glutamylcysteine synthetase (γ-ECS), but not of glutathione synthetase (GS5), significantly enhanced Cys, γ-EC and GSH in phloem exudates. Since growth of poplar is not affected by either γ-ECS or GSS overexpression, phloem transport of thiols seems to be controlled by the source rather than the sink strength.