Visible light causes cellular metabolism effects even in cases where the tissue or specimen does not have specialized photoreceptors, report biologists in PNAS Early Edition. That could be a problem for the many researchers who assume natural light or fluorescent microscopy causes no change in living tissue.
J. Brian Robertson from Middle Tennessee State University and colleagues studied changes in yeast respiration in the presence of blue and green light, finding that light can be used to control short period respiratory oscillations in yeast.
“Under certain conditions bursts of light can be used to kick start a non-respiring culture of yeast into (respiratory) oscillation,” says Robertson, “and that continuous bright light application can be used to destroy an oscillation.”
Molecular biologists have known for some time that blue light can affect respiration in yeast and other organisms as the photons destroy cytochromes, and other molecules that contain iron. Cytochromes serve as catalysts in oxidation-reduction reactions.
“This effect had previously only been described (in yeast) as affecting growth rates and oxygen consumption,” Robertson says. “We discovered light also affected metabolic rhythms” Robertson says. “Most other organisms have specialized photoreceptors that permit light to modulate their rhythms. But here, yeast use an unexpected mechanism for modulating their rhythms.”
The oscillations under study were short period (so-called ultradian) rhythms having periods between 90 and 250 minutes. The authors conclude that light affects circadian respiratory oscillations by inhibiting the activity of cytochromes, thereby inhibiting electron transport and oxidative phosphorylation. For the moment, it is uncertain if this mechanism is adaptive, or simply a side-effect. Whatever the case, Robertson is hopeful that the properties of light can be turned to the task of controlling yeast in culture. Trained in a lab that studied approximately 24-hour circadian rhythms, “it seemed like an obvious question for me to ask whether yeast rhythms were affected by light as well,” he says.
But the most broad-reaching implication of the study, he says, is that lab scientists working with living tissues have a new variable to consider. As they shine a light on living cells and tissues, they may be changing the very system they’re seeking to understand.