26 Feb 2015

Unlocking the Secrets of Photosynthesis

From Our Changing World, 9:20 pm on 26 February 2015

By Alison Ballance

Sun shining through a tree's leaves. Plants take energy from sunlight, water and carbon dioxide, and use photosynthesis to produce sugars and oxygen, splitting water in the process.

Plants take energy from sunlight, water and carbon dioxide, and use photosynthesis to produce sugars and oxygen, splitting water in the process. Photo: Wikimedia Commons

“From my perspective plants are machines that capture light. And they’re able to take light energy and turn it into chemical energy, and use that process to extract carbon dioxide from the atmosphere and generate sugars. So leaves are factories turning solar energy into food.” Julian Eaton-Rye

Biochemist Julian Eaton-Rye, from the University of Otago, is fascinated by the process of photosynthesis, and in awe of plants’ ability to do things like split water.

Julian’s work focuses on the water splitting process, which happens in Photosystem II, near the beginning of photosynthesis. “What’s remarkable about that process,” says Julian,” Is that if you want to do that yourself, you’re going to have to heat it up to about 2000 degrees Centigrade, because you’re breaking it apart – and water is phenomenally stable. So to break it apart is a thermodynamic challenge, and Photosystem 2, this first step in photosynthesis, has evolved just once in evolution – about 2.5 billion years ago – to split water and use this abundant source of material as a fuel source to drive the biosphere.”

Julian uses the cyanobacterium Synechocystis as his model plant, and his research focuses on proteins and how they are constantly broken and repaired.

Chloroplasts, visible in the cells of Plagiomnium affine or the many-fruited thyme moss, carry out photosynthesis.

Chloroplasts, visible in the cells of Plagiomnium affine or the many-fruited thyme moss, carry out photosynthesis. Photo: CC BY-SA 3.0 Kristian Peters

“The chemistry of Photosystem 2 is so challenging that it actually damages the enzymes as it operates normally,” says Julian. “So there’s this cost, that to use this wonderful source of energy the protein structure actually damages itself and needs to be repaired.”

Julian believes that if we can understand how this protein repair mechanism works, it could lead, for example, to more efficient photovoltaic panels – at the moment these have a limited life, but Julian believes it should be possible to greatly extend this.

Another result of understanding the water splitting process could be the creation of low temperature water-splitting technology to produce hydrogen as a source of fuel. Modifying plants so they can better survive in arid environments, or hot and cold environments, is another possible outcome that could lead to better food production.

Biochemist Julian Eaton-Rye with flasks of antibacterial which are helping him understand how photosynthesis can split water.

Biochemist Julian Eaton-Rye with flasks of antibacterial which are helping him understand how photosynthesis can split water. Photo: RNZ / Alison Ballance

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