By quieting their "noisy" photosynthetic antennae networks and tuning them to their environments, solar-powered organisms achieve remarkably efficient light energy harvesting, according to a network theory report. It takes a new approach to investigating the question of how power-output of photosynthetic organisms is organized so efficiently, identifying a universal concept that underlies this impressive ability that could be used to improve the design of future solar technologies. In a related Perspective, Christopher Duffy writes, "The finding ... is important, because it suggests that the evolutionary driving force behind the development of photosynthetic antennae is not maximization of efficiency but the cancellation of noise." During photosynthesis, photons from the sun are absorbed by a network of light energy-harvesting antennae and transferred as electronic excitations to the reaction centers, where they are converted into chemical energy that plants and other photosynthetic organisms use to drive their metabolism. Light-harvesting antenna complexes - a modular assembly of various protein and light-absorbing pigment molecules - are remarkably effective: They can achieve nearly perfect quantum efficiency, converting each absorbed photon into a chemically usable electron despite ever-changing lighting conditions and complex physiology. Although light-harvesting varies in form and function across the range of photosynthetic life, whether a common set of "design" principles underlies such effective systems is unknown. Trevor Arp and colleagues applied a network theory model to reveal the most basic requirements needed for optimal light-harvesting in three distinct photosynthetic niches - full sun, under a canopy of leaves and underwater. Arp et al. found that by using two pigments that absorb slightly different wavelengths of light in a narrow range of the spectrum, photosynthetic organisms in different environments mitigate sudden changes in solar energy and minimize the potential for energy fluctuations or "noise" in the output of light-harvesting antennae. The results show how light-harvesting antennae can be evolutionarily tuned for maximum power conversion. They also provide a basis to explain the variation in wavelength dependence observed among some photosynthetic organisms.
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Journal
Science