Scientists discover molecule behind birds' magnetic sense
Some birds, notably migratory species, are able to detect the Earth's magnetic field and use it to navigate. New results from a team of Franco-German researchers suggest that light-sensitive molecules called cryptochromes could be the key to the birds' magnetic sense.
Cryptochromes are photoreceptors which are sensitive to blue light, and they are involved in a number of processes linked to the circadian cycle, such as growth and development.
Birds' ability to detect magnetic fields is affected by light; this 'sixth sense' only works properly in the presence of blue or green light, while light of other wavelengths disrupts the magnetic sense.
The scientists realised that the cryptochromes could well be involved in the perception of the magnetic field, as they have all the physical and chemical properties needed, notably the absorption of blue and green light and the formation of 'radical pairs' - molecules which respond to magnetic fields. Crucially, the retina of birds' eyes is rich in cryptochromes.
Unable to test their hypothesis on migratory birds, the researchers turned to a laboratory plant, Arabidopsis thaliana, with similar properties. It is known that the activation of their cryptochromes by blue light influences the behaviour of these plants; for example it inhibits the growth of the hypocotyle (stem).
To determine whether the magnetic field influences the function of the cryptochromes, researchers from France's National Centre for Scientific Research (CNRS) and universities in Frankfurt and Marbourg grew the plants in the presence of blue and red light and magnetic fields of varying strengths. They found that increasing the magnetic field only increases the inhibition of the growth of the hypocotyle in the presence of blue light. When red light is used, the plant uses other photoreceptors called phytochromes, and the growth of the hypocotyle is not affected by changes in the magnetic field. Furthermore, mutant plants which have no cryptochromes are also insensitive to changes in the magnetic field.
The study shows for the first time that in plants, the work of the cryptochromes is affected by magnetic fields and suggests that the mechanisms of magnetic field perception in plants, and by extension in migratory birds, use the same photosensitive molecules. The researchers also suggest that, as cryptochromes have been strongly conserved throughout evolution, all biological organisms could have the ability to detect magnetic fields, even if they do not use them.