Science & Technology (Commonwealth Union) – Photosynthesis has been a crucial process often learnt in basic biology. Many different scientists from across the world played a crucial role in what we know about photosynthesis today. Dutch physiologist, Jan Igenhousz played a crucial role in what we know about photosynthesis.
To endure different atmospheres where photosynthesis is challenging, some organisms rely on unusual adaptations. Scientists from Osaka Metropolitan University in Japan, have discovered that a freshwater alga can tap into far-red light as an extra energy source by arranging ordinary chlorophyll in a remarkable configuration.
Far-red light falls outside the most efficient range for photosynthesis in many organisms. However, in places such as shaded forests and cloudy waters where this light is prevalent, plants and algae still manage to photosynthesize, effectively generating energy from extremely limited options.
Ritsuko Fujii, the lead author and associate professor at the Graduate School of Science and the Research Center for Artificial Photosynthesis at Osaka Metropolitan University pointed out that while certain cyanobacteria rely on specialized chlorophylls to capture far-red light, many plants and algae accomplish a similar outcome by reorganizing standard chlorophyll a into cooperative clusters within their photosynthetic antenna systems.
On its own, chlorophyll a cannot absorb far-red light. This raises the question of how these organisms are able to carry out photosynthesis under such conditions.
To investigate, the research team examined the freshwater eustigmatophyte alga Trachydiscus minutus. This species accumulates large amounts of a light-harvesting protein capable of utilizing far-red light. Although the alga can photosynthesize under normal lighting, the abundance of this protein becomes particularly advantageous in dim environments where light is scarce.
Fujii indicated that the organism generates a unique photosynthetic antenna known as a red-shifted violaxanthin–chlorophyll protein (rVCP), despite containing only chlorophyll a, this structure is able to absorb far-red light.
By applying cryo-electron microscopy, the research team mapped the structure of rVCP with a high resolution of 2.4 Å. Their analysis revealed a previously unknown configuration: a tetramer built from two distinct heterodimers. This unusual arrangement positions chlorophyll a molecules very close together, enabling them to create unusually large clusters of pigments.
To explore how this configuration influences light absorption, the scientists combined the structural findings with multiscale quantum-chemical modelling.
“Our analysis showed that three chlorophyll clusters within each heterodimer play a major role in absorbing far-red light,” explained Fujii. “Importantly, this absorption arises purely from energy delocalization across multiple chlorophyll molecules, independently of the charge-transfer effects that are thought to drive similar red-shifted systems.”
These results uncover a fundamentally new way that organisms adjust the wavelength of light they absorb. In this system, the protein framework precisely manages how identical chlorophyll molecules interact, without altering the pigment chemically. This explains why these organisms can thrive in challenging environments.
The discovery also carries real-world potential. Certain eustigmatophytes are valued for their ability to accumulate oils, making them strong candidates for sustainable biofuel production. Using organisms capable of photosynthesis under far-red light could allow oil generation in places that are usually unsuitable.
The distinctive tetrameric arrangement of rVCP could also serve as a novel template for protein engineering. Since the positioning of pigments is directed by the protein’s sequence, this structure may guide the design of artificial or improved photosynthetic systems.
Fujii indicated that as there is growing interest in extending photosynthesis into the far-red spectrum to enhance global productivity, their next step is to understand how this complex transfers captured energy to the photosystem and explore ways to optimize that process.
These findings were reported in the Journal of the American Chemical Society.
