How aminomethylphosphonic acid (AMPA), the main glyphosate metabolite, interferes with chlorophyll biosynthesis?

Abstract

Aminomethylphosphonic acid (AMPA) has been proposed to interfere with chlorophyll biosynthesis in photoautotrophic organisms – which may explain its greater toxicity to plants in relation to animals. By using the aquatic macrophyte Lemna minor , we investigated the AMPA toxicity and its effects on chlorophyll biosynthesis. Environmentally relevant concentrations (35–50 µg l -1 ) of AMPA reduced L. minor chlorophyll concentration with an EC 10 and EC 50 of 1.3 and 902.9 µg AMPA l -1 after seven days of exposure respectively but did not affect plant fresh weight/growth rate (EC 10 and EC 50 of 178.6/244.4 and 11,922.2/12,513.2 µg AMPA l -1 , respectively). AMPA decreased the activity of glycine decarboxylase (GDC), leading to glycine accumulation and glutamate (Glu) deprivation in plants. The lack of Glu prevents the synthesis of δ-aminolevulinic acid (ALA) in chloroplasts, interfering on chlorophyll synthesis. The negative effect of AMPA on chlorophyll concentration was reversible by supplementing growth media with Glu or ALA. The presence of AMPA in the aquatic ecosystems may contribute to their alteration by its negative effects on photosynthetic organisms through chlorophyll biosynthesis inhibition. Furthermore, we should stress out that AMPA could be toxic for animals and humans due to known toxicity of glycine induced by GDC inhibition. • Environmental relevant concentrations of AMPA reduce chlorophyll concentrations. • AMPA decreased the activity of the enzyme glycine decarboxylase (GDC). • AMPA induces the lack of glutamate and prevents the synthesis of ALA in chloroplasts. • Due to its negative effect on GDC, AMPA could be toxic for animals and humans.