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Title: Final Report for research on The Glucose 6-Phosphate Shunt Around the Calvin-Benson Cycle

Abstract

In this research, photosynthetic carbon metabolism was studied to identify mechanisms by which plants store energy from sunlight as carbon compounds, especially sugars. Conditions were identified in which carbon appeared to flow backwards from outside the photosynthetic compartment (chloroplast) back into it. A specific gene product was manipulated to make the flow bigger or smaller. Preventing the flow (by eliminating the gene) had little effect on plant growth but increasing the flow, by overexpressing the gene, caused the plants to become extremely sensitive to changes in light. Plants with the gene overexpressed had high rates of cyclic electron flow, the photosynthetic electron transport pathway that occurs when plants need more of the energy molecule ATP. These and other observations led us to conclude that a metabolic pathway that is normally turned off because it is counter-productive during photosynthesis, in fact occurs at about 10% of the rate of normal photosynthesis. This creates an inefficiency but may stabilize photosynthesis allowing it to cope with the very large and rapid changes that leaves experience such as the hundred-fold changes in light intensity that can occur in seconds on a partly cloudy day. We also concluded that the back flow of carbon intomore » chloroplasts could be important at high rates of photosynthesis allowing increased rates of starch synthesis. Starch synthesis allows plants to store sugars during the day for use at night. At high rates of photosynthesis starch synthesis becomes very important to protect against end-product inhibition of photosynthesis. This research identified two metabolic pathways that extend the primary carbon fixation pathway called the Calvin-Benson cycle. These pathway extensions are now called the cytosolic bypass and the glucose 6-phosphate shunt. This improvement in our understanding of carbon metabolism of photosynthesis will guide efforts to increase photosynthesis to increase production of food, fuel, and fiber.« less

Authors:
 [1]
  1. Michigan State Univ., East Lansing, MI (United States)
Publication Date:
Research Org.:
Michigan State Univ., East Lansing, MI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Contributing Org.:
Michigan AgBioResearch
OSTI Identifier:
1405284
Report Number(s):
DOE-MSU-0008509-1
DOE Contract Number:  
SC0008509
Resource Type:
Technical Report
Resource Relation:
Related Information: Jaikumar NS, Snapp SS, Sharkey TD (2016) Older Thinopyrum intermedium (Poaceae) plants exhibit superior photosynthetic tolerance to cold stress and greater increases in two photosynthetic enzymes under freezing stress compared with young plants. J Exp Bot 67: 4743-4753Sharkey TD (2015) Understanding carbon partitioning and its role in determining plant growth. Plant Cell Environ 38: 1963-1964Sharkey TD (2016) What gas exchange data can tell us about photosynthesis. Plant Cell Environ 39: 1161-1163Sharkey TD (2017) A dichotomy resolved: Plant growth can control the rate of starch accumulation. Plant, Cell & Environment: in pressSharkey TD, Weise SE (2016) The glucose 6-phosphate shunt around the Calvin-Benson cycle. J Exp Bot 67: 4067-4077Weise SE, Carr DJ, Bourke AM, Hanson DT, Sharkey TD (2015) The arc mutants of Arabidopsis with fewer large chloroplasts have a lower mesophyll conductance. Photosyn Res 124: 117-126Yang JT, Preiser AL, Li Z, Weise SE, Sharkey TD (2016) Triose phosphate use limitation of photosynthesis: short-term and long-term effects. Planta 243: 687-698
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; Photosynthesis; starch; Calvin-Benson cycle; carbon metabolism

Citation Formats

Sharkey, Thomas D. Final Report for research on The Glucose 6-Phosphate Shunt Around the Calvin-Benson Cycle. United States: N. p., 2017. Web. doi:10.2172/1405284.
Sharkey, Thomas D. Final Report for research on The Glucose 6-Phosphate Shunt Around the Calvin-Benson Cycle. United States. https://doi.org/10.2172/1405284
Sharkey, Thomas D. 2017. "Final Report for research on The Glucose 6-Phosphate Shunt Around the Calvin-Benson Cycle". United States. https://doi.org/10.2172/1405284. https://www.osti.gov/servlets/purl/1405284.
@article{osti_1405284,
title = {Final Report for research on The Glucose 6-Phosphate Shunt Around the Calvin-Benson Cycle},
author = {Sharkey, Thomas D.},
abstractNote = {In this research, photosynthetic carbon metabolism was studied to identify mechanisms by which plants store energy from sunlight as carbon compounds, especially sugars. Conditions were identified in which carbon appeared to flow backwards from outside the photosynthetic compartment (chloroplast) back into it. A specific gene product was manipulated to make the flow bigger or smaller. Preventing the flow (by eliminating the gene) had little effect on plant growth but increasing the flow, by overexpressing the gene, caused the plants to become extremely sensitive to changes in light. Plants with the gene overexpressed had high rates of cyclic electron flow, the photosynthetic electron transport pathway that occurs when plants need more of the energy molecule ATP. These and other observations led us to conclude that a metabolic pathway that is normally turned off because it is counter-productive during photosynthesis, in fact occurs at about 10% of the rate of normal photosynthesis. This creates an inefficiency but may stabilize photosynthesis allowing it to cope with the very large and rapid changes that leaves experience such as the hundred-fold changes in light intensity that can occur in seconds on a partly cloudy day. We also concluded that the back flow of carbon into chloroplasts could be important at high rates of photosynthesis allowing increased rates of starch synthesis. Starch synthesis allows plants to store sugars during the day for use at night. At high rates of photosynthesis starch synthesis becomes very important to protect against end-product inhibition of photosynthesis. This research identified two metabolic pathways that extend the primary carbon fixation pathway called the Calvin-Benson cycle. These pathway extensions are now called the cytosolic bypass and the glucose 6-phosphate shunt. This improvement in our understanding of carbon metabolism of photosynthesis will guide efforts to increase photosynthesis to increase production of food, fuel, and fiber.},
doi = {10.2172/1405284},
url = {https://www.osti.gov/biblio/1405284}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Oct 30 00:00:00 EDT 2017},
month = {Mon Oct 30 00:00:00 EDT 2017}
}