Hormesis with Herbcides Glyphosate as a Case Study
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
Inhibits auxin translocation Effects of naptalam on L. paucicostata growth
Unknown mode of action Effects of scopoletin on L. paucicostata growth
N-phosphonomethylglycine (glyphosate) n Simple zwitterionic amino acid n First synthesized in 1950 by Henri Martin (Cilag Co. ) for unknown purposes n First tested for herbicidal activity by Monsanto Agric. Products in 1970.
Highly translocatable n 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" <Sandy. Morgan@ARS. USDA. GOV> >80% of transgenic crops were glyphosate resistant in 2006
Other uses n Sugarcane ripener
Inhibition of EPSP synthase by glyphosate Funke, Todd et al. (2006) Proc. Natl. Acad. Sci. USA 103, 13010 -13015 Copyright © 2006 by the National Academy of Sciences
Three-dimensional structure of CP 4 EPSP synthase Funke, Todd et al. (2006) Proc. Natl. Acad. Sci. USA 103, 13010 -13015 Copyright © 2006 by the National Academy of Sciences
Mechanism of action of glyphosate Phosphoenolpyruvate + Erythrose 4 -phosphate DAHP synthase Shikimate pathway Shikimate 3 -phosphate EPSP synthase Glyphosate Chorismate Anthranilate IAA Secondary products Arogenate Phenylalanine and Tyrosine Tryptophan Protein Plant defenses Phytoalexins Lignin
More carbon from other pathways flows into the shikimate pathway Phosphoenolpyruvate + Erythrose 4 -phosphate DAHP synthase Salicylate? Protocatechuate and other benzoates Shikimate pathway Shikimate 3 -phosphate EPSP synthase Glyphosate Shikimate Chorismate Anthranilate IAA Secondary products Arogenate Phenylalanine and Tyrosine Tryptophan Protein Plant defenses Phytoalexins Lignin
Previous report of hormesis with glphosate n Wagner, R. et al. , (2003) Phytotoxic activity of root absorbed glyphosate in corn seedlings (Zea mays L. ). Weed Biol. Manag. 3, 228232. n 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 Glyphosate 7. 2 g/ha 3. 6 g/ha Glyphosate Control
Eucalyptus grandis
Shikimate in leaves, 45 days after application of glyphosate to Eucalyptus grandis hormesis
Conventional soybean
Growth of glyphosate-resistant transgenic soybean The application of rates from 1. 8 to 720. 0 g/ha did not affect the growth of glyphosate-resistant transgenic soybean
Effects of glyphosate on growth of L. paucicostata
Potential mechanism(s? ) of hormesis by glyphosate Phosphoenolpyruvate + Erythrose 4 -phosphate DAHP synthase Shikimate 3 -phosphate EPSP synthase 1 Acridone alkaloids Chorismate Indole alkaloids Indole phytoalexins Anthranilate Arogenate Phenylalanine and Tyrosine Tryptophan Hydroxycinnamates Lignins Indole glucosinolates 2 Alkaloids Flavonoids + Isoflavanoids
Barley measured 4 days after spraying glyphosate (g/ha)
10 -day old barley treated and then evaluated 4 days later Leaf length (cm/plant) Glyphosate (g/ha) Shoot length (cm/plant) Glyphosate (g/ha)
10 -day old barley treated and then evaluated 4 days later Root dry wt increase (g/plant) Glyphosate (g/ha) 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) Glyphosate (g/ha) Relative growth rate (d-1) Glyphosate (g/ha)
Used Affymetrix barley chip n Not a whole genome chip n 25, 500 genes
Microarray experiment RNA samples 2 8 20 h 12 -day-old plants sprayed with 5, 10 and 20 g/ha glyphosate Growth 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 n 2 h upregulated - 12 genes n 8 h upregulated - 2 genes n 20 h upregulated - 3 genes n 2 h downregulated - 0 genes, n 8 h downregulated - 0 genes, n 20 h downregulated - 3 genes.
2 hours 1. Cytochrome P 450 -like protein - 3. 4 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 H 2 A. 9 - wheat dbj|BAA 07279. 1| protein H 2 A – 6. 1 X 9. 9 e-37 expressed protein; protein – 3. 9 X 10. Unknown – 4. 7 X 11. Cysteine proteinase – 8. 4 X 12. Thionine Osthi 1 – 14. 7 X
8 hours 1. Cysteine proteinase – 8 X 2. En/Spm-like transposon protein – 7 X
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 - -1. 5 X 2. Unknown (different than up-regulated none genes) - -1. 1 3. GA-regulated protein, GASA precursor - - 1. 25
Functional breakdown of affected genes
Further work needed n Cell wall aspects n Lignification n Anatomical measurements n Photosynthetic aspects (Cedergreen) n Hormonal aspects
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