Presentation on theme: "Hormesis with Herbcides: Glyphosate as a Case Study Stephen O. Duke, Joanna Bajsa, Scott R. Baerson Natural Products Utilization Research Unit, Agricultural."— Presentation transcript:
Hormesis with Herbcides: Glyphosate as a Case Study Stephen O. Duke, Joanna Bajsa, Scott R. Baerson Natural Products Utilization Research Unit, Agricultural Research Service, United States Department of Agriculture, University, MS, USA Nina Cedergreen Univ. Copenhagen, Tåstrup, Denmark Edivaldo Velini Univ. São Paulo State, Botucatu, Brazil
Effects of naptalam on L. paucicostata growth Inhibits auxin translocation
Effects of scopoletin on L. paucicostata growth Unknown mode of action
N-phosphonomethylglycine (glyphosate) Simple zwitterionic amino acid First synthesized in 1950 by Henri Martin (Cilag Co.) for unknown purposes First tested for herbicidal activity by Monsanto Agric. Products in 1970.
Highly translocatable Co-translocates with sucrose to metabolic sinks (i.e., meristems). Gougler and Geiger, Plant Physiol. 68: 668 (1981)
~ 50 X resistance factor Nandula et al., J. Agric. Food Chem. – in press (2007)
"Morgan, Sandy" >80% of transgenic crops were glyphosate resistant in 2006
Mechanism of action of glyphosate Phosphoenolpyruvate + Erythrose 4-phosphate DAHP synthase Shikimate 3-phosphate EPSP synthase Chorismate Anthranilate Tryptophan Arogenate Phenylalanine and Tyrosine Glyphosate Plant defenses Phytoalexins Lignin IAA Secondary products Shikimate pathway Protein
Phosphoenolpyruvate + Erythrose 4-phosphate DAHP synthase Shikimate 3-phosphate EPSP synthase Chorismate Anthranilate Tryptophan Arogenate Phenylalanine and Tyrosine Glyphosate Plant defenses Phytoalexins Lignin IAA Secondary products Shikimate pathway Protein Shikimate Protocatechuate and other benzoates More carbon from other pathways flows into the shikimate pathway Salicylate?
Previous report of hormesis with glphosate Wagner, R. et al., (2003) Phytotoxic activity of root absorbed glyphosate in corn seedlings (Zea mays L.). Weed Biol. Manag. 3, Schabenberger, O. et al., (1999) Statistical test for hormesis and effective dosage in herbicide dose-response. Agron. J.
Increase in leaf dry weight 55 days after application of glyphosate to Pinus sp.
Increase in leaf area 30 days after application of glyphosate to coffee (Caffea arabica)
Increase in leaf area 25 days after application of glyphosate to Sorghum bicolor
Shikimate in leaves, 20 days after application of glyphosate to Sorghum bicolor hormesis
Shikimate in leaves, 30 days after application of glyphosate to coffee plants hormesis
Glyphosate Control 1.8 g/ha 3.6 g/ha 7.2 g/ha Glyphosate Control
Shikimate in leaves, 45 days after application of glyphosate to Eucalyptus grandis hormesis
Growth of glyphosate-resistant transgenic soybean The application of rates from 1.8 to g/ha did not affect the growth of glyphosate-resistant transgenic soybean
Effects of glyphosate on growth of L. paucicostata
Barley measured 4 days after spraying glyphosate (g/ha)
10-day old barley treated and then evaluated 4 days later Leaf length (cm/plant)Shoot length (cm/plant) Glyphosate (g/ha)
10-day old barley treated and then evaluated 4 days later Root dry wt increase (g/plant)Shoot dry wt increase (g/plant) Glyphosate (g/ha)
10-day old barley treated and then evaluated 4 days later Plant dry weight increase (g/plant) Relative growth rate (d-1) Glyphosate (g/ha)
Used Affymetrix barley chip Not a whole genome chip 25,500 genes
Microarray experiment 12-day-old plants sprayed with 5, 10 and 20 g/ha glyphosate h RNA samplesGrowth determined at 5 days after treatment
g glyphosate/ha Fresh weight (g/plant)
RTPCR of phenyalalaine ammonia-lyase Light off Light on
RTPCR of DAHPS Light off Light on
Very little in terms of a dramatic response 2h upregulated - 12 genes 8h upregulated - 2 genes 20h upregulated - 3 genes 2h downregulated - 0 genes, 8h downregulated - 0 genes, 20h downregulated - 3 genes.
2 hours 1. Cytochrome P450-like protein X 2. Putative cell wall protein – 3.1 X 3. Very-long-chain fatty acid condensing enzyme – 3.3 X 4. putative GDSL-motif lipase/hydrolase-like protein – 3.1 X 5. Structural protein – 4.1 X 6. Putative proline-rich protein – 3.1 X 7. Unknown – 4.7 X 8. Histone H2A.9 - wheat dbj|BAA | protein H2A – 6.1 X 9. 9e-37 expressed protein; protein – 3.9 X 10. Unknown – 4.7 X 11. Cysteine proteinase – 8.4 X 12. Thionine Osthi1 – 14.7 X
8 hours 1. Cysteine proteinase – 8 X 2. En/Spm-like transposon protein – 7X
20 hours Upregulated 1. Unknown (different than at 2 h) – 4 X 2. Ethylene-responsive transcriptional coactivator-like protein – 2.3 X 3. En/Spm-like transposon protein – 2 X Downregulated 1.Polygalacturonase-inhibiting protein X 2.Unknown (different than up-regulated none genes) GA-regulated protein, GASA precursor
Functional breakdown of affected genes
Further work needed Cell wall aspects Lignification Anatomical measurements Photosynthetic aspects (Cedergreen) Hormonal aspects