The mystery about plants' internal 'light switches' is slowly being unravelled, thanks to theoretical chemists in Sweden.

Phytochromes in plants are light receptors that are responsible for releasing chemicals that trigger processes in cells like germination or flowering. They work when exposed to red light with a specific wavelength. Two different phytochrome forms exist: one is active and one inactive. Switching between them depends on the light?s wavelength.

Bo Durbeej at Uppsala University and colleagues have used quantum chemical techniques to decipher what happens when the different phytochromes isomerise. They think that the initial step is photochemical, and subsequent isomerisations are heat driven. So far, Durbeej has looked at a single phytochrome in the gas phase, which in itself is a quantum chemical breakthrough, but the hope is to one day understand what happens when the phytochromes interact with surrounding proteins.

Katharine Sanderson