Photosynthetic algae evolve unique pigments to shield from sunlight and boost energy efficiency

Photosynthetic algae evolve unique pigments to shield from sunlight and boost energy efficiency
by Riko Seibo
Tokyo, Japan (SPX) Oct 23, 2025

Marine green algae have developed a remarkable defense against the harmful effects of excess sunlight, according to a study by Osaka Metropolitan University and its international research partners. The investigation revealed that a pigment called siphonein acts as a protective shield, enabling algae to maintain efficient photosynthesis without risking damage from overexposure to light.

The research focused on the marine alga Codium fragile, which, like land plants, contains light-harvesting complexes equipped with chlorophyll to absorb sunlight. However, Codium fragile stands out due to its incorporation of unique carotenoids, notably siphonein and siphonaxanthin, which allow effective use of green light under water.

"Organisms use carotenoids to quickly dissipate excess energy, or quench these triplet states, through a process called triplet-triplet energy transfer (TTET)," said Ritsuko Fujii, associate professor at Osaka Metropolitan University. Using a specialized electron paramagnetic resonance spectroscopy method, the team directly observed that Codium fragile's carotenoids eliminate potentially damaging chlorophyll triplet states far more effectively than in spinach plants.

The scientists discovered that siphonein's placement in the light-harvesting antenna structure is crucial for this energy-dissipating process, and further quantum chemical simulation confirmed the electronic structure's key role in preventing oxidative harm while improving photosynthetic performance.

Algae's evolutionary adaptation, shown in this study, not only helps them withstand bright marine sunlight but may pave the way for bio-inspired improvements in solar energy technology. The team now hopes to identify structural features in carotenoids that maximize energy quenching, potentially revolutionizing the design of artificial photosynthetic and renewable energy systems.

"Our research has revealed that the antenna structure of photosynthetic green algae has an excellent photoprotective function," stated Alessandro Agostini, University of Padua, co-lead author of the study. "We hope to further clarify the structural characteristics of carotenoids that increase quenching efficiency, ultimately enabling the molecular design of pigments that optimize photosynthetic antennae," Fujii said.

Research Report:Siphonein enables an effective photoprotective triplet quenching mechanism in green algal light-harvesting complexes