Just one hour of sunlight disperses more energy on the earth’s surface than is consumed by humans over an entire year. But for us humans, capturing and directing this energy to meet our needs is still a work in progress. Evolution has done a much better job.
All plants derive energy from the sun. They take light and convert it into food, creating as a by-product the oxygen we rely on. But if they’re exposed to too much light, absorbing this excess energy can cause damage to the plant’s cells. So how is it that these plants and other organisms that depend on the sun for energy manage to regulate the amount of sunlight they take in when it’s cloudy and avoid overexposure on sunny days?
A new paper published in Nature Chemistry
outlines the discovery of two of the mechanisms used in green algae and moss to protect against this excess energy. This defence is called photoprotection. Researchers at MIT and the University of Verona are behind the promising finding, which could have important implication for improving solar energy technology and increasing crop yields.
“It’s a real challenge for photosynthetic systems to adjust to deal with a fluctuating energy sources,” says Gabriela Schlau-Cohen
(MIT), the lead author on the paper and a CIFAR Azrieli Global Scholar
. They have overcome that challenge by evolving a dynamic set of mechanisms that allow them to respond to constantly changing environments in ways machinery we build doesn’t.
Schlau-Cohen and her colleagues explored how a single light-harvesting protein, LHCSR1, known to be responsible for activating the release of excess energy as heat and for converting light energy into heat, does its job.
Using an extremely sensitive microscope capable of examining a single protein, the researchers measured what happens to the protein when exposed to different light conditions and found that it acts as a safety valve, ensuring that energy that exceeds the capacity of the downstream photosynthetic machinery is instead released as heat.
“We found that this dissipation doesn’t just occur through one process, but it occurs through these two different ways that are designed to respond to two different types of changes that you see in solar intensity,” said Schlau-Cohen.
The first photoprotective mechanism gets switched on quickly, within seconds of a sudden change in light such as the appearance of the sun from behind cloud. The second gets switched on more gradually in response to a slower change like the progressive increase of light at sunrise.
Plants tend to turn on photoprotection very quickly in response to sun and they are slow to turn it off, Schlau-Cohen says. That helps plants to survive, but it means that they are not producing as much biomass as they could. A study published in Science
last November showed that speeding up the steps involved in photoprotection boosts biomass production by 15 percent under natural field conditions. If the process was further optimized, it could increase production even more.
Schlau-Cohen’s colleagues at the University of Verona are now creating mutated versions of the LHCSR1 protein, which the researchers plan to test to see if they have the ability to produce more biomass while still offering some photoprotection.
“The more we learn about mechanisms the smarter we can be about how we upregulate. For example maybe we want to turn on some things and turn off some other things as opposed to just turn up everything,” said Schlau-Cohen.