Team provides new insight into photosynthesis

Apr 04, 2013
Advanced optical probes using femtosecond lasers enable light harvesting processes to be examined in exquisite detail. Anticlockwise from top right: Purple bacteria and the structure of the light harvesting complex that gives these cells their distinctive purple color. This special protein incorporates molecules of bacteriochlorophyll and carotenoid to capture the energy from sunlight. The lower part of the figure shows the protein data recorded from two-dimensional laser spectroscopy. Credit: Evgeny Ostroumov

Pigments found in plants and purple bacteria employed to provide protection from sun damage do more than just that. Researchers from the University of Toronto and University of Glasgow have found that they also help to harvest light energy during photosynthesis.

Carotenoids, the same pigments which give orange color to carrots and red to tomatoes, are often found together in plants with chlorophyll pigments that harvest solar energy. Their main function is photoprotection when rays of light from the sun are the most intense. However, a new study published in Science this week shows how they capture blue/green light and pass the energy on to chlorophylls, which absorb red light.

"This is an example of how nature exploits subtleties that we would likely overlook if we were designing a solar energy harvester," says Greg Scholes, the D.J. LeRoy Distinguished Professor in the Department of Chemistry at the University of Toronto and lead author of the study.

A series of experiments showed that a special "dark state" of the – a hidden level not used for at all – acts as a mediator to help pass the energy it absorbs very efficiently to a chlorophyll pigment.

The researchers performed broadband two-dimensional electronic spectroscopy – a technique used to measure the and its dynamics in atoms and molecules – on light-harvesting proteins from purple bacteria. The aim was to characterize in more detail the whole sequence of quantum mechanical states of carotenoids that capture light and channel energy to bacteriochlorophyll molecules. The data revealed a signature of a special state in this sequence that was predicted decades earlier, and sought ever since. The results point to this state's role in mediating from carotenoid to bacteriochlorophyll.

"It is utterly counter-intuitive that a state not participating in light absorption is used in this manner," says Scholes. "It is amazing that nature uses so many aspects of a whole range of quantum mechanical states in carotenoid molecules, moreover, and puts those states to use in such diverse ways."

The other significant aspect of the work is that the existence of these dark states has been speculated for decades and that the report by Scholes and his colleagues is the clearest evidence to date of their existence.

"We found a smoking gun for the state predicted decades ago and argued about ever since," says Scholes.

"The energy transfer processes in natural light-harvesting systems have been intensively studied for the last 60 years, yet certain details of the underlying mechanisms remain controversial. Our work really clears up this particular mystery," says Richard Cogdell, the Hooker Professor of Botany at the University of Glasgow, co-author of the report.

"It makes us look differently at the potential of molecules as building blocks," Scholes says. "Just imagine one molecule, a carotenoid, that can be used to harvest light, photoprotect, convert to a 'safety valve' in bright to dissipate excitations, or even be employed as a heat transducer by such as are found in the black hole on the island of San Andros in the Bahamas."

Explore further: Friction harnessed by proteins helps organize cell division

More information: "Broadband 2D Electronic Spectroscopy Reveals a Carotenoid Dark State in Purple Bacteria," by E.E. Ostroumov et al. Science, 2013.

Related Stories

Discovery brings organic solar cells a step closer

Jan 15, 2009

Inexpensive solar cells, vastly improved medical imaging techniques and lighter and more flexible television screens are among the potential applications envisioned for organic electronics.

Lessons to be learned from nature in photosynthesis

Sep 23, 2011

Photosynthesis is one of nature's finest miracles. Through the photosynthetic process, green plants absorb sunlight in their leaves and convert the photonic energy into chemical energy that is stored as sugars ...

Researchers Identify Key Molecules in Photosynthesis

Dec 02, 2009

(PhysOrg.com) -- Chemistry professor Harry Frank led an international group of researchers that identified the molecules in algae which direct the organisms to convert sunlight into oxygen. The findings may ...

Recommended for you

For cells, internal stress leads to unique shapes

11 hours ago

From far away, the top of a leaf looks like one seamless surface; however, up close, that smooth exterior is actually made up of a patchwork of cells in a variety of shapes and sizes. Interested in how these ...

Adventurous bacteria

12 hours ago

To reproduce or to conquer the world? Surprisingly, bacteria also face this problem. Theoretical biophysicists at Ludwig-Maximilians-Universitaet (LMU) in Munich have now shown how these organisms should ...

Revealing camouflaged bacteria

14 hours ago

A research team at the Biozentrum of the University of Basel has discovered an protein family that plays a central role in the fight against the bacterial pathogen Salmonella within the cells. The so cal ...

User comments : 0

More news stories

More vets turn to prosthetics to help legless pets

A 9-month-old boxer pup named Duncan barreled down a beach in Oregon, running full tilt on soft sand into YouTube history and showing more than 4 million viewers that he can revel in a good romp despite lacking ...

Revealing camouflaged bacteria

A research team at the Biozentrum of the University of Basel has discovered an protein family that plays a central role in the fight against the bacterial pathogen Salmonella within the cells. The so cal ...

New clinical trial launched for advance lung cancer

Cancer Research UK is partnering with pharmaceutical companies AstraZeneca and Pfizer to create a pioneering clinical trial for patients with advanced lung cancer – marking a new era of research into personalised medicines ...

'Chief Yahoo' David Filo returns to board

Yahoo announced the nomination of three new board members, including company co-founder David Filo, who earned the nickname and formal job title of "Chief Yahoo."