London: In a finding that paves the way for fourth-generation biofuels and dramatic crop improvements, scientists have got a fix on how plants regulate the amount of carbon dioxide they use after taking it in from the air.

For instance, when there is not enough sunlight, plants put the brakes on the amount of carbon dioxide they use to make food. But as sunlight increases, the brakes are rapidly released, in a process called the Calvin cycle.

In a new study, researchers at the University of Essex have found that this variable speed control mechanism works thanks to a special relationship between two enzymes 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 are unable to function, slowing the Calvin cycle. The darker it is, the more PRK-GAPDH partnerships are formed.

Conversely, greater sunlight helps them break apart rapidly, speeding up the Calvin cycle.

Said Christine Raines, who led the study: "If we can understand these processes, we can use the knowledge to develop and improve food and biofuel crops."

Tom Howard, who contributed to the research, added: "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." IANS