Brussels, 01 Sep 2004
A group of scientists from the Netherlands, the UK and the US has discovered how the component parts of photosynthesis fit together within the cell membrane - and the process is much more complex than previously thought.
Photosynthesis is the reaction that allows plants and bacteria to take in sunlight and convert it into chemical energy by turning carbon dioxide and water into carbohydrates and oxygen.
'Photosynthesis is the single most important chemical reaction on Earth and it is fascinating to see for the first time how nature has overcome the problem of harvesting and utilising solar energy,' said project participant Professor Neil Hunter from the UK's University of Sheffield.
Although scientists have known for some time about the individual components involved in photosynthesis and their structure, this is the first time that anyone has succeeded in establishing how they all fit together and work as a system.
Professor Hunter explained how the project team used an Atomic Force Microscope that 'feels' the shape of individual molecules and then converts this into a picture illustrating the system within an individual cell membrane. 'We have discovered nature's way of collecting light for photosynthesis,' he said.
'We already know that during photosynthesis, light is collected by an antenna made up of two light harvesting [LH] complexes - LH1 and LH2 - and then passed to a reaction centre where it is converted into chemical energy. However, these were like individual jigsaw pieces and we had yet to see the full picture,' said Professor Hunter.
The research showed how groups of LH2 complexes pick up light and then pass it around among themselves until the light comes across an LH2 complex that is touching one of the larger LH1 complexes. The energy then circulates around the LH1 complex or passes to another LH1 until it moves on to the reaction centre.
'We found that the LH2 complexes are structured in an antenna-like shape, and when light is scarce they cooperate by joining together to allow them to make the best possible use of the limited light available,' said Professor Hunter. The LH1 complexes are each attached to their own reaction centre, and the team believes that if an LH1 takes in light whilst its reaction centre is 'busy', then it will keep passing the energy on to neighbouring LH1 complexes, until an unoccupied reaction centre is found.
'We hope to test this particular theory further, but the purpose of both these systems would be to maximise the efficiency of photosynthesis. The process of harvesting light energy is over 95 per cent efficient, which is an incredible figure,' said Professor Hunter.
Professor Hunter believes that this new knowledge not only increases understanding of photosynthesis, but also has implications for molecular science: 'By looking at the world on an individual molecular level, scientists have the opportunity to learn more about an incredible number of biological systems and processes.'