Glyphosate Transport and Early Effects on Shikimate Metabolism and Its Compartmentation in Sink Leaves of Tomato and Spinach Plants

Abstract

Glyphosate (N[phosphonomethyl]glycine) applied to an assimilate-exporting leaf of tomato or spinach plants is translocated via the phloem to the young growing areas of the shoot apex and root where it causes the rapid accumulation of shikimate and shikimate 3-phosphate to up to 16% of the dry weight or these tissues. Using the technique of non-aqueous fractionation of spinach leaves it was shown that the herbicidal target of glyphosate, the shikimate pathway enzyme 5-enolpyruvlyshikimate 3-phosphate synthase, is located within the chloroplast and that, in the presence of glyphosate. shikimate 3-phosphate accumulates in the same organelle, while shikimate was preferentially localized in the vacuolc. The major part of [l4C]glyphosatc imported into the leaf via the phloem was detected in the cytosolic fraction of the mesophyll cells.