Too much sun is not a good thing, for people or for plants
- Sep 20, 2017
- Homepage News, Faculty & Staff, Research, Biochemistry, Plant Biology
“You’ve got a harvest of sunshine, a sky full of blue,” according to the lyrics of an old Jimmy Dean song. But too much sun is not necessarily a good thing. To protect ourselves, we can apply sunscreen. What do plants do?
Fluorescence methods reveal differences in photosystem II activity of the wild type (left two) and MPH2 mutant (right two) plants following high light stress growth. Mutants displayed severely reduced PSII activity compared to the wild type.
Scientists have an increasingly sophisticated understanding of mechanisms that ensure efficient photosynthesis under laboratory-controlled light conditions. But less is known about the regulation of photosynthesis when plants experience rapid and extreme changes in sunlight, which can potentially cause harmful effects on photosynthetic efficiency and productivity.
Rob Last, Michigan State University Barnett Rosenberg Professor, and postdoctoral researcher Jun Liu, are working to better understand these mechanisms. The results of their research were published this month in the Proceedings of the National Academy of Sciences (PNAS).
The MSU researchers have discovered the critical role played by MPH2, a protein in the lumen of the chloroplast thylakoid membrane required for the repair of photosystem II (PSII) when damaged by excess light energy. They found that the loss of MPH2 in the flowering plant Arabidopsis thaliana causes PSII repair deficiency under changing light.
“Photosynthesis has a balancing act. Energy from sunlight is essential for conversion of carbon dioxide and water into biomass and chemical energy. Too much energy from the sun destroys the ability of PSII to function, and these damaged reaction centers must be repaired to allow them to get back to the business of photosynthesis,” said Last, who holds joint appointments in MSU’s Departments of Plant Biology, and Biochemistry and Molecular Biology in the College of Natural Science.
They have also discovered that mutants in this protein—and many other previously described PSII repair mutants—suffer when grown under dynamically changing light conditions.
“This is in contrast to mutants that are defective in preventing damage, which do not seem to suffer under dynamic light conditions,” Last said. “This difference between repair and protection mechanisms has potential importance for designing 'resilient' crop plants that are productive under stressful and dynamic conditions.”
“The amount of sun that shines on plants fluctuates enormously on timescales from seconds to seasons,” Liu said. “I find it fascinating that this molecular mechanism allows photosynthetic organisms to thrive despite these huge changes.”
The researchers found that repair is not only required for PSII maintenance under static photoinhibitory light conditions but is also a regulatory mechanism enabling plant adaptation to natural, ever-changing light environments. These findings advance the understanding of the elaborate PSII repair system in higher plants.
"Testing the importance of PSII repair to algae and cyanobacteria under fluctuating light conditions may offer insight into the evolution of photosynthesis," Liu said. "We are excited about the possibility that understanding the role of MPH2 and other PSII repair proteins could lead to breeding and genetic engineering of crops that can endure harsh climates and dynamic environments to sustainably meet the increasing demands for food, fuel and fiber in this time of changing climate and rapid population growth."