C3 + C4 = C2?

3 June 2019 09:00
Dr Marjorie Lundgren

Scientist believes that a grass using a rare, flexible form of photosynthesis may contain clues to help us feed the world.

Dr Marjorie Lundgren stumbled across the plant that now fascinates her while researching her PhD into different forms of photosynthesis - the process by which plants use sunlight to turn CO2 and water into the sugars that make up a plant’s biomass and nutrients.

Scientists, including a group at Lancaster University, have been expending a huge amount of money and brainpower trying to improve photosynthesis in key crops, particularly rice, to improve yields and resilience to climate change.

Marjorie, who has recently joined the Lancaster University Photosynthesis Group from MIT and Harvard University, believes that one promising route to improvement may lie in a very rare form of photosynthesis, called C2. It was this form of photosynthesis she came across in the grass Alloteropsis semialata in the herbarium collection at the Royal Botanic Gardens in Kew.

“The vast majority of plants use a type of photosynthesis called C3, including staple grains such as rice and wheat,” explains Marjorie, who was brought up on a farm in Connecticut. “About 3% of flowering plants, like maize and sugarcane, use C4 photosynthesis: it’s a kind of turbo-charged photosynthesis.”

C3 plants perform well in cool, wet places, but in hot, dry, sunny environments they suffer from a process called photorespiration, which can reduce their yield by up to a quarter. In these environments C4 plants perform better.

Alloteropsis semialata, the species Marjorie studied at Kew, is unusual because it contains both C3 and C4 plants, and also plants using the much rarer C2 form of photosynthesis.

“The more I saw of these C2 plants in the wild, the more I realised that they seem to have the ability to be a bit plastic, behaving like C3 plants in cooler environments and C4 plants in hotter places. Their physiology is flexible to the environment.”

There is a current scientific push to adapt C3 crops like rice, which grows in very hot environments, to use the C4 mechanism – it’s hoped this will improve yields and help feed the growing human population. But this is proving very complex. So Marjorie wondered if the C2 system might provide a quicker, easier way forward. “On paper at least, C2 plants should definitely be more efficient than C3 plant in hot dry environments, and they seem to have this extra flexibility to boot.” It’s these hypotheses that Marjorie has come to Lancaster to test out.

“The Lancaster Environment Centre is probably the best place for photosynthesis research in the northern hemisphere with eminent scientists like Steve Long and Martin Parry and emerging stars like Elizabete Carmo-Silva, so I’m joining research that is world class,” said Marjorie, who has been awarded an Leverhulme Early Career Fellowship to support her work.

“We are still learning about C2 photosynthesis. It was discovered early in the 1980s and has only been found in about 50 species from 20 lineages. We know that C2 evolved in brassicas, a family including broccoli, kale, and oilseed rape, where a lot of our nutrients come from, while C4 never evolved in that family: so focusing on C2 could mean we can improve yields in crops that are important to our nutrition.

“One of first things I want to do is establish the productivity advantages of C2 plants compared to C3 and C4. We don’t have a good sense of how much better they are exactly in terms of biomass, yield, water and nitrogen efficiencies.”

Marjorie is curating a seed collection of C2 plants and their close C3 and C4 relatives and will grow them all in a common environment in a glasshouse to measure if, at end of the day, the C2 plants produce more seeds and biomass, and whether they grow faster and by how much.

She also wants to find out in which specific environments the C2 plants are better than C3 or C4 plants and how flexible they are.

“I’m doing a simple experiment on environmental variability. I’ll repeatedly shift the growing environment, so they will have a stretch of time in a cool, wet and shady environment and then another in a hot, dry and bright environment, moving them back and fourth for over a year. What I expect is that under these variable conditions, which are exactly the kind of environments we will experience more with climate change, the C2 plants will outperform their C3 and C4 relatives.”

Marjorie is also excited by the close links the Lancaster team have with the farming community and private sector and hopes these ties will provide better opportunity for her research to be translated into crops soon.

“It means that the research that I do has a higher potential to be translational, for my ideas to increase yield and start feeding people more nutritious crops as well.”

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