Photosynthesis needs tuning - The solution lies under the plant’s bonnet

Need more food? More energy? Less CO₂? How tuning plant engines offers a solution.

Unlike us, plants can use sunlight to produce their own nutrients and energy. This process is called photosynthesis and it runs the World. If we want to keep the planet and its growing population running in a sustainable way, we will need plants to produce far more food, energy and applicable biomass than they do now. Photosynthesis, the green engine of life on Earth, needs tuning.

This is something mankind has never done before. We have hybridized and bred plants for centuries to create the best varieties. Here and there we have genetically adapted crops to increase their yield. We have given plants water, good soil and artificial fertiliser. But we have never worked on the plant’s engine before. Until now.

The first results are in, and they are spectacular. Dutch plant scientist Wanne Kromdijk, working under the supervision of Steve Long at the University of Illinois (US), recently published the results of experiments with tobacco plants in the magazine Science. These scientists were able to increase the yield of the tobacco plant by 15 per cent. This is a huge step in breeding terms and was achieved by tweaking a component of the photosynthesis process of the plant.

Long had previously discovered how the gearbox of the photosynthesis engine works. The crux is that while light powers photosynthesis to the benefit of the plant, too much light can damage the machinery of photosynthesis. If a plant is in the blazing sun, part of the absorbed light energy is simply dumped instead of being used for photosynthesis. The process shifts photosynthesis down a gear, so to speak, and only goes up again when light intensity diminishes. This means that a plant standing in fluctuating light is constantly changing gears. And this is the case for most plants due to the moving leaves of neighbouring plants or overhanging trees that sometimes block sunlight but at other times let it shine through.

Changing gear

Once the light intensity diminishes, it takes some time before the plant changes to a more efficient gear. During this period photosynthesis is not as efficient as it could be and the gear change takes longer for some plants than for others. Steve Long’s team discovered the reason for this difference and built a faster gearbox into the tobacco plant. With spectacular results.

Steve Long works in the US and UK, and is part of a large research consortium that is currently being established of scientists from 48 institutions in 17 countries. They are working hard to obtain finance for the Photosynthesis 2.0 research programme in the next EU framework programme, which starts in 2020.

The type of result achieved by Kromdijk and Long will certainly help, says René Klein Lankhorst from Wageningen University, one of the initiators: “It shows how much progress can be achieved by playing with photosynthesis. And it’s not the only spectacular result. Our British colleague Christine Raines studied an enzyme complex in an entirely different part of the engine. She was able to accelerate its functioning, which resulted in a 30 per cent yield increase. And there are countless other parts of the engine that could be adjusted.”  

But Klein Lankhorst is keen to underline that this is not where the story ends. Examples of super-photosynthesis is not only found in recent science, but also in nature. The Formula 1 of photosynthesis involves desert plants, the seeds of which sometimes have to wait for years for rain. What’s more, when the rain finally comes they must do everything very quickly: seeding, rooting, developing stems, leaves and flowers, and distributing new seeds.

Klein Lankhorst: “It is incredible, you can almost see the plants grow. But for desert plants it is a necessity. And to focus everything on super-fast growth, they’ve abandoned other activities that are less important, such as disease resistance. This means you can’t just put genes from a desert plant into our crops. But although you have to be careful, it’s clear that photosynthesis can be accelerated.

“People often think that nature is very efficient. It is, but only in natural conditions. The crops we grow were not born for agriculture; we took them from the forests and placed them in fields. If they had completely adapted to these new conditions they would perform much better. A field of potatoes, for example, uses only 0.5 per cent of the incident solar energy. This could be 5 to 10 per cent.”

But we don’t even have to get that far. A doubling of production would already resolve the food demand of the growing global population and the demand for biomass for a green economy. And this doubling would also make a world of difference to the climate. The Paris Climate Agreement states that global CO₂ emissions must be reduced by 20 gigatons per year. Photosynthesis in agricultural crops uses 14 gigatons of CO₂ a year worldwide. The CO₂ the crops absorb is obviously partly released again as we consume or burn them. But if photosynthesis was accelerated, part of the extra CO₂ absorbed could be stored in some way, in the soil for example, and this could make a considerable contribution to the climate agreement goals – a difference of some 4 gigatons CO₂ a year, Klein Lankhorst estimates.

This is all possible. And it would have guaranteed results, leading to more economic activity and growth. And yet it isn’t easy to obtain financing for research into accelerating photosynthesis. Thankfully, opinions in Brussels are shifting: the European Commission has declared yield improvement in agriculture a priority in view of the major world problems (food, energy, climate). Research into photosynthesis fits right in. But in the Netherlands itself, it remains difficult to get things moving.

Over recent years Klein Lankhorst led a national research programme called Biosolar Cells. It studied both the acceleration of photosynthesis in plants and algae, and the mimicking  of nature: artificial photosynthesis for the production of, for example, hydrogen, which is a fuel, or methanol, a raw material for the chemical industry,.

But Biosolar Cells was financed by the Natural Gas Funds, which were at that time partly used for knowledge development and scientific research. The government closed down this source of funding, however, bringing to an end programmes such as Biosolar Cells and many more.

Wageningen University and Utrecht University may receive an investment subsidy for lab facilities in both cities for accurate experimental research into photosynthesis. Klein Lankhorst: “This would allow us to see exactly what happens in the plant, above and below ground.” Fundamental scientific research, in fact. But for a follow-up of the former research programme, the government demands cooperation with the industry. And companies are hard to convince that investing in a long-term project is a good investment.

Klein Lankhorst: “I haven’t been able to persuade the obvious candidates, such as energy companies. They show an interest in a few wind turbines, perhaps a field of solar cells here or there, but that’s it. The chemical sector will require much more biomass to move towards green chemistry, but doesn’t want to compete with food production as that is a fight they’d lose. We can make sure that the biomass will be available. Yet, they’re not interested. Reducing climate risks is of the essence to insurers, but they aren’t interested in investing in research into reducing those risks either.”

Breeding companies

Companies that will definitely benefit from adjustments to the engine of photosynthesis are those involved in breeding and seed production; a global sector in the Netherlands. But even they aren’t jumping at the chance to invest. Not yet, anyway. They do see opportunities on the horizon but beyond their timeline. “Great idea,” many of them say. “Come back in five years.”

This is a typically Dutch problem Klein Lankhorst explains: the gap between fundamental research and innovation. “We know that we will make significant progress, but we need ten to 15 years to realise applicable and responsible applications. For instance, when accelerating photosynthesis, you don’t want the crop to need any more water or artificial fertiliser than is absolutely necessary because climate change will reduce the amount of water available to agriculture.

"This means you have to look carefully at how to  develop such plants. It will take time to ensure that the extra productivity goes to where it is needed, such as the fruit or grain. And there are many other preconditions we need to take into account. But we will be successful. And we don’t need that much money, especially compared to other branches of science like particle physics or nuclear fusion. An international research programme into photosynthesis would require approximately one billion for ten years.”

A bargain, Klein Lankhorst laughs: “Over the same period, a multinational would spend the same amount on their Friday socials alone.”

What is photosynthesis?

Plants, algae and some bacteria produce from carbon dioxide (CO₂) and water (H₂O) sugars (C₆H₁₂O₆), which can be used for many purposes, including as a building block for cell material, as an energy source or as a nutrient. These sugars are the result of photosynthesis.

Judging by the end product, photosynthesis might be thought to be a simple process. But appearances can be deceiving as the underlying machinery is extremely complex. Photosynthesis is a combination of many biophysical processes and chemical reactions which are catalysed by various enzymes. The mechanism is so complicated that the last of these enzymes was only identified several years ago. And it’s still unknown how many genes regulate the photosynthesis process; it could be hundreds or even thousands.

The photosynthesis engine consists of two large blocks. In the first, sunlight is used to make energy-rich substances that can be stored in the cell. This block is known as the light reaction. In the second, the dark reaction, the stored energy is used to make glucose from carbon dioxide and water.

Unravelling photosynthesis is a story that started in the mid-seventeenth century, when Jan van Helmont, a physician and scientist from Brussels, showed that as plants became larger the soil in which they grew did not become lighter. Helmont concluded that water was the source of their growth, not the soil.

It took a century and a half before it became clear this was only half the story, and that plants also needed CO₂ to grow. This discovery was the result of an observation by the versatile British scientist Joseph Priestley, who saw that a candle under a bell jar would go out long before it was burnt to the stump, but that this didn’t happen when a plant was under the same jar. Priestley spoke of ‘injured air’ that was healed by the plant.

The Dutch physician Jan Ingenhousz then showed that plants needed sunlight to do so. Not long after, Swiss scientists Jean Senebier and Nicolas-Théodore de Saussure discovered that ‘injured air’ is actually CO₂ absorbed by the plant. In exchange, the plant emits oxygen which allows the candle to burn.

Oxygen is a waste product of photosynthesis which is emitted into the atmosphere by the plant. This emission is one of the largest environmental disasters in the history of the Earth. Oxygen is an aggressive and destructive substance which the plant isn’t able to process. It wasn’t part of the Earth’s original atmosphere, but currently takes up some 20 per cent.

With their emissions, plants created their own potential destruction and they had to adapt significantly to survive. But on the other hand, via photosynthesis oxygen has made possible the existence all life forms which are not self-sufficient, including mankind.

Source: www.trouw.nl