A team of Biotechnology and Biological Sciences Research Council
(BBSRC) funded scientists at the University of Essex has discovered a new
mechanism that slows the process of carbon dioxide fixation in plants.
The research, published today (4 March 2008) in the Proceedings of the
National Academy of Sciences, increases our understanding of this process,
which may ultimately lead to crop improvement and ?fourth generation?
biofuels. The mechanism, which helps to regulate the way in which plants
absorb carbon dioxide (CO2) from the atmosphere and turn it into sugars,
acts by putting the brakes on sugar production when there is not enough
energy from sunlight available. As sunlight increases, the brakes are
rapidly released and carbon dioxide fixation speeds away.

Plants are dependent on sunlight to capture carbon dioxide, which is
turned into important sugars via a process called the Calvin cycle. As a
result, as the amount of sunlight varies during the day (e.g. through cloud
cover or shading from other plants), they must also be able to vary the
speed at which they capture carbon dioxide from the atmosphere. This ensures
that when there is a lot of sunlight, it is taken full advantage of but that
when sunlight drops, so does CO2 uptake. This ability to maximise energy use
is important for plants and prevents the loss of important metabolic
resources. Because they essentially stay in one place, plants must have many
unique abilities to adapt to their environment as it changes around them.

The question is how does this variable speed control actually work"
The BBSRC-funded research shows for the first time how the Calvin cycle can
be regulated in response to a changing light environment via a molecular
mechanism. There is a special relationship between two enzymes that are
involved in the Calvin cycle ? phosphoribulokinase (PRK) and
glyceraldehyde-3-phosphate dehydrogenase (GAPDH). When light levels
decrease, the two enzymes tend to stick together and therefore cannot
function, thus slowing the Calvin cycle. The darker it is, the more
PRK-GAPDH partnerships are formed and the slower the Calvin cycle becomes.
In the light, they break apart rapidly and the Calvin cycle is allowed to
speed up.

This fundamental research has revealed a novel mechanism and provides
a better understanding of the regulation of CO2 fixation in plants. This
work will underpin strategies to increase the amount of carbon dioxide
absorbed by plants thereby increasing yield for food and biofuel production,
and may ultimately feed into the development of ?fourth generation?
biofuels.

Research Leader, Professor Christine Raines of the University of
Essex, said: ?Although this research focuses on the fundamental biological
processes that plants use, ultimately, if we can understand these processes,
we can use the knowledge to develop and improve food and biofuel crops.?

Dr Tom Howard, who contributed to the research, said: ?Plants have
evolved a fascinating way to cope with variations in their local
environments. Unlike animals, they cannot move on to look for new food
sources. This research helps to unlock one way that plants deal with the
ultimate variable ? the amount of sunshine they receive.?

Professor Nigel Brown, BBSRC Director of Science and Technology said:
?With a growing world population and increasing demands for energy we need
to consider new ways to improve food and fuel production. Sophisticated
basic research in areas which have been studied for many decades, such as
this work funded by BBSRC, furthers our understanding of natural processes
that have the potential to be harnessed to meet future challenges.?


[www.bbsrc.ac.uk]