Application of ³¹P-NMR spectroscopy to glyphosate studies in plants: Insights into cellular uptake and vacuole sequestration correlated to herbicide resistance

Glyphosate is the world's most widely used herbicide due to favorable attributes of low cost, low toxicity, and high efficacy in controlling a wide range of weed species. The genetic engineering of important crops with the glyphosate-tolerant trait has led to extensive and largely exclusive glyphosate usage in many areas. The resulting selective evolutionary pressure has resulted in the emergence of glyphosate-resistant weed biotypes. Glyphosate contains a phosphonate (-CPO₃ ^2-) chemical group, with variable protonation depending upon pH, that provides for convenient detection and monitoring via ³¹P NMR in plant tissue extracts as well as in vivo. Insights provided through ³¹PNMR studies of weed species exposed to glyphosate have improved our understanding of herbicide uptake and compartmentalization, resulting in key insights regarding resistance mechanisms. For example, we have previously reported the discovery and characterization of glyphosate vacuole sequestration as the principal resistance mechanism in horseweed (Conyza canadensis) and in ryegrass (Lolium spp.) from several continents. Herein, we expand our prior published ³¹P-NMR studies to include additional weed biotypes, characterizing glyphosate uptake, vacuole sequestration and chloroplast exclusion.