Ditte Bøgeskov Master Defence: Glyphosate’s impact on Sorghum bicolor

All are welcome!

Supervisors:
Birger Lindberg Møller, Prof.
Kirsten Jørgensen, Assoc. Prof.
Lasse Janniche Nielsen, Ph.D.

Title: Towards a deeper understanding of glyphosate’s impact on Sorghum bicolor

Abstract: Research in sustainable crops with promising capacities to meet future supply demands and climate changes is crucial - now more than ever. Glyphosate is a herbicide, developed to meet some of the demands, but little is known about glyphosate’s impact on crop value and metabolism, e.g. according to its dose and the number of days after application.

This study will assess some of the speculations about glyphosate’s impact on one of the most important crops in the world, namely Sorghum bicolor.

In sorghum, dhurrin is a cyanogenic β-glucoside of an α-hydroxynitrile derived from tyrosine. Upon tissue disruption, β-glucosidases and α-hydroxynitrilase are brought into contact with dhurrin; indorsing its degradation and the release of toxic hydrogen cyanide. Another constituent of an ancient plant defense is the presence of lignin, which greatly lowers the biomass digestibility of forage sorghum. To improve the digestibility of sorghum feedstuff, small doses of glyphosate have shown beneficial. A greater insight into the correlation between glyphosate treatment and the complex metabolism of these limiting factors on the nutritional value of forage sorghum is elucidated in this study.

Here, LC-MS metabolic profiling of leaf dhurrin, lignin precursor metabolites, and aromatic amino acid compositions was carried out. Furthermore, the LC-MS method was optimized by replacing the commonly used Zorbax SB-C18 column with a Zorbax SB-C8 column to allow for the retention and separation of the highly polar glyphosate and its degradation product, AMPA. To investigate glyphosate’s impact on gene expression levels of biosynthetic enzymes around glyphosate’s site of action in the shikimate pathway, sequences of primer pairs were designed for future research with qPCR. Also, primers were designed to transcripts of dhurrin biosynthetic enzymes CYP79A1, CYP71E1, and UGT85B1.

Together, these findings contribute to a deeper understanding of glyphosate treatment on S. bicolor, and provide a solid steppingstone for continuous research on this intriguing subject.