Photosynthesis and Carbon Fixation
Study on the eGects of glyphosate on
glyphosate-sensitive and glyphosateresistant
soybean plants*
• Glyphosate-sensitive plants
• Leaf photosynthesis was rapidly inhibited by glyphosate
• Marked increase in glutathione synthesis (antioxidant defenses)
• Levels of glutamine, asparagine and arginine increased while phenylalanine was
sharply decreased.
"Glyphosate produced a rapid, marked, and sustained inhibition of
photosynthetic CO2 assimilation in the glyphosate-sensitive line."
• Glyphosate resistant plants
• Chlorophyll content significantly reduced in leaves compared to controls
• Very high levels of glyphosate were detected in the leaves
• Increased pools of oxidized glutathione and ascorbate (antioxidant defenses)
• Rubisco expression was reduced by a factor of 25.
*Pedro D Vivancos et al. Plant Physiology 2011; 157: 256-268.
Rubisco is the most common enzyme on the planet, and it plays an essential role in photosynthesis.
Phosphoenolpyruvate Carboxylase (PEPC)
• PEPC is a ubiquitous enzyme in plants, also often present in archaea,
cyanobacteria and green algae
• It is an integral enzyme in photosynthesis to assimilate CO2 in green plants
• The terminal sequence QNTG is highly conserved across multiple phyla
• Glyphosate was shown experimentally to suppress activity of PEPC*
• Replacement of the terminal glycine with the negatively charged amino
acid aspartate causes up to a thousand-fold decrease in catalytic
eOiciency**
- Substitution of glyphosate for the terminal glycine would have similar
devastating consequences
*N de Maria et al., J Agric Food Chem. 2006;54(7):2621-8.
**W Xu et al. JBC 2006; 281(25): 17238-17245.
Terminal Glycine Essential in PEPC
*Figure 1. W Xu et al. JBC 2006; 281(25): 17238-17245.
Cloud Seeding & Marine Phytoplankton
“DMS: The Climate Gas You’ve Never Heard Of”*
• Dimethylsulfide (DMS) is a small sulfur-containing gas that plays a significant role in climate change
• DMS decreases the amount of solar radiation that reaches the Earth's surface by inducing cloud formation
• DMS is synthesized from dimethylsulfoniopropionate (DMSP) by marine phytoplankton in shallow ocean waters
• Emiliania huxleyi (E huxleyi) is an important marine phytoplankton species that synthesizes DMSP**
*Scott Dodd. Woods Hole Oceanographic Institute, July 17, 2008.
https://www.whoi.edu/oceanus/feature/dms-the-climate-gas-youve-never-heard-of/
**M Kamlow. MSc Thesis. Norwegian University of Science and Technology. 2013.
http://www.diva-portal.org/smash/record.jsf?pid=diva2%3A699830&dswid=-6180