Plants And Mammals Respond To Light In Similar Way

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Article Date: 01 Jul 2008 - 0:00 PDT

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A new report published in the open-access journal PLoS Biology examines the effect that light has on humans and animals. Most of us are familiar with how light affects the growth and development of plants (phototropism, for example, describes how plants grow towards light), but researcher Nathalie Hoang and colleagues set out to explore light's impact on humans and mammals.

Plants have photoreceptor proteins called cryptochromes that take in blue light to help the plant grow and develop seedlings. Cryptochromes are also present in mammals, and the researchers studied those found in flies, mice, and humans. In humans, cryptochromes have been shown to have an effect on regulating the circadian clock (the 24 hour cycle of biochemical, physiological or behavioral processes), but we still do not know much about exactly how these cryptochromes operate.

In plants, blue light exposure leads to a reduction in flavin pigments, which activates the cryptochromes and begins growth and seedling development. Hoang and colleagues used this idea to expose flies, animals, and humans to blue light. The researchers measured the number of oxidized flavins after blue light exposure and found that prolonged exposure led to a decrease in the number of flavins.

The similarity in how blue light affects flavin levels in plants and animals, however, should not lead to an assumption that flavins affect circadian rhythms in the same way. For example, mice that lacked the cryptochromes Mcry1 and Mcry2 seemed to completely lose circadian rhythm behaviors (such as wheel-running), but these behavioral changes occurred with or without light exposure.

The authors write: "We demonstrate that light induces a change in the redox state of flavin bound to the receptor in both human and Drosophila cryptochromes. Photoreduction from oxidized flavin and subsequent accumulation of a semiquinone intermediate signaling state occurs by a conserved mechanism that has been previously identified for plant cryptochromes. These results provide the first evidence of how animal-type cryptochromes are activated by light in living cells. Furthermore, human cryptochrome is also shown to undergo this light response. Therefore, human cryptochromes in exposed peripheral and/or visual tissues may have novel light-sensing roles that remain to be elucidated."

Human and Drosophila cryptochromes are light activated by flavin photoreduction in living cells
Hoang N, Schleicher E, Kacprzak S, Bouly JP, Picot M, et al.
PLoS Biology (2008). 6(7): e160.
doi:10.1371/journal.pbio.0060160
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About PLoS Biology

PLoS Biology is an open-access, peer-reviewed general biology journal published by the Public Library of Science (PLoS), a nonprofit organization of scientists and physicians committed to making the world's scientific and medical literature a public resource. New articles are published online weekly; issues are published monthly. For more information, visit http://www.plosbiology.org

About the Public Library of Science

The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. For more information, visit http://www.plos.org

Written by: Peter M Crosta
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