There is an ongoing food crisis that is becoming more severe every year, even if many don’t openly see it in more developed parts of the world. Global actions have improved overall food security for many impoverished and subsistence farming regions, but the larger looming crisis has not been diminished. With limited agricultural space on the planet, the future of agriculture relies on improving the potential output of food we grow on the same amount of land. And, as always, to allow that improvement to occur for all farmers around the world, not just a subset of them. 

How To Consume Sunlight

We’ve previously discussed the idea of expanding the photosynthetic capabilities of plants to then allow them to grow faster and have more consistent yields. The potential for this exists because there are several areas in the complex web of how photosynthesis functions that are quite inefficient. Their evolution over time and through natural selection became functional enough to serve plants for their nutritional and respiratory needs, since it wasn’t overall beneficial for them to have that faster growth in regards to their own survival. That left multiple parts of the photosynthetic process that have the potential for improvement for our own purposes as farmers and growers of the plants. A slightly more in-depth discussion of this can be found in that prior article.

The complications of feeding everyone extend to far more than just population, of course. Even the act of keeping current yields and outputs of food is at risk with the increasing stresses coming from climate change. Extensive temperature variations, drought and flooding both, and other such stresses are a threat to global agriculture as a whole and work is needed to protect from those in addition to improving existing plant growth and development. And, out of these, temperature will remain the general highest problem as average temps rise outside of the usual growing regions and farmers must either find a way to improve the thermotolerance of the plants they grow or move to different climes that are likely to have much more nutritionally poor soils. 

Creating Better Consumption

Methods to accomplish this revolve around the type of photosynthesis done by plants. The most common form used by farm crops, over 80% of them, is referred to as C3 metabolism and is distinguished from the two other forms of processing carbon dioxide into energy referred to as C4 and CAM. The C3 plants are the more moderate of all the options, preferring temperate areas with a good amount of sunlight and average warm temperatures, but not too much in either category. This is unlike C4 that are able to withstand greater temperatures and drought conditions and the specific uses for CAM that allows plants with the latter to grow in completely arid environments. The problem with high temperatures for C3 plants, without getting into a lecture about photosynthesis metabolism as a whole, is that high heat reduces the efficiency of the process of converting CO2 to oxygen and producing energy. 

Because of this, a lot of scientific research is being put into finding ways to modify C3 plants to convert them to C4 metabolizers. But this isn’t just a straightforward change and there are a lot of moving components that need to be changed on the biochemical level to be successful. That’s why it is still an ongoing effort. There are other alternative pathways, however, than just changing to a C4 system. Thus, there’s been a number of research teams trying to see which is more efficient and if, perhaps, specific pathways can be tailored to make different cultivars of crops good at photosynthesis under stresses like high heat without requiring the extensive amount of reformatting that a full C4 system would entail. Which brings us to a research group at the University of Illinois Urbana-Champaign in the university’s Carl R. Woese Institute for Genomic Biology. These researchers chose this topic as a part of a larger international initiative called Realizing Increased Photosynthetic Efficiency (RIPE) that generally aims to enhance photosynthetic capabilities of agricultural plants around the world.

Breathing and Eating

The aim of this particular project was to create a synthetic alternative photorespiration pathway that mimicked some aspects of C4 plants and that protects against the negative stress of high temperatures and excessive light exposure. This was done by genetically transforming tobacco plants to use both malate synthesis and glycolate dehydrogenase within the chloroplasts. They also combined these changes with an RNA interference sequence to reduce the creation of transporters that would otherwise move glycolate out of the chloroplast and into other photosynthetic systems the plant normally uses it for. More glycolate could then be used in this dehydrogenase system to more efficiently fuel the respiration processes that would also enhance photoprotection in the photosynthesis pathways under high light stress.

What they saw after doing so was a significant increase of 5 to 18% better carbon fixation during photosynthesis under temperatures of 104 degree Fahrenheit (40 degrees Celsius). This effect was similarly shown under field testing under induced higher than average growth temperatures, with the modified plants seeing a smaller loss of daily net carbon uptake as compared to the wild type and the total biomass produced by the end of the growing season in the field had a 17-18% improvement in the modified tobacco plants. When adding in canopy leaf and stem losses as well, the modified plants overall had a 37% greater biomass. Though, it should be noted, this is in relation to retained biomass as the increased temperatures served to reduce total growth for all plants, just much less for the modified plants. 

These yield loss mitigations are just one part of a larger process being worked on in different labs, but it shows that even specific components being altered in the photosynthesis and photorespiration pathways can have a massive effect on resulting plant growth and yield. Since climate change has already majorly impacted crops like wheat, rice, and barley, the ability to retain those yields at higher temperatures and allow for farmers to remain in the nutrition-rich temperate soils would be a far better alternative than having to move the growing regions used around the world to less prosperous soils and environments. 

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Photo CCs: 0281Tobacco fields in Laoac, Pangasinan 06 from Wikimedia Commons

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