Glowing Plants Indicate Internal Clocks in Action

You can't fool Mother Nature, and it looks as if she won't let you mess with her timetable for life, either. Inside most plants, animals, and microorganisms is an internal biological clock. This clock controls many life functions in a rhythmic pattern, including 24-hour patterns known as circadian rhythms, which help to govern sleep, body temperatures, eating patterns and reproduction. It is because of this internal clock that international travelers feel jet lag, and it also makes Alaskans wake up in the morning in the dark of winter whether we want to or not.

Circadian rhythms interest scientists because these internal clocks control such a wide variety of biological processes in many species. Circadian rhythms are controlled by genes that may be similar in such diverse organisms as bacteria and humans. Identifying which genes regulate the daily cycles of plants may give insight into solving clock-related disorders in humans, such as insomnia and depression.

Until recently, it has been difficult to monitor the effects of the internal clock on some physical processes. While it is relatively simple to measure a change in human body temperature or the onset of fatigue, in organisms like plants it's not always easy to know when the end of photosynthesis occurs. Now, thanks to some innovative research by several scientists, a plant's internal clock can simply be lighted up.

According to an article in Science magazine, associate professor Steve Kay with the University of Virginia, manipulated the DNA of a plant from the mustard family and inserted a firefly gene that controls the production of light. A firefly creates light when an enzyme within the firefly called luciferace breaks down molecules of luciferin. Kay took the firefly's luciferace gene and attached it to part of a gene from the mustard plant that helps to kick-start photosynthesis every morning and stop it every night. Kay inserted this new piece of DNA into other mustard plants.

Kay checked for luciferace by spraying the mustard plants with luciferin, and was delighted to see the samples gave off a green glow corresponding to the plants' circadian rhythms. The plants glowed faintly in the early morning and brightly during the day. As evening approached, the glow faded. Kay now had a visual, measurable indication of the effects of the circadian rhythm in plants.

The next step for Kay and his colleagues was to identify the gene that controls the circadian rhythms and find out which genetic flaws harm it. To do this, they soaked some of the seeds of the genetically altered plant in a chemical that caused mutations. These seeds were then grown into seedlings, sprayed with luciferin, and monitored to see if any glowed at the wrong times. Most of the mutations occurred in genes that were not related to the biological clock, but a few were. These mutants had clocks that were hours longer or shorter than the normal 24-hour cycle of the weed.

Another research group wanted to estimate the total number of clock-controlled genes in a blue-green algae. The scientists, from Vanderbilt, Texas A&M and several Japanese universities, didn't target a specific gene area such as Kay did previously with the mustard plant gene that controls photosynthesis; they instead randomly inserted a luciferace gene from luminescent bacteria into the algae.

They predicted that whenever the luciferase gene landed near a clock-controlled light gene, light would be produced in a rhythmic pattern corresponding to the circadian rhythms of the algae. Surprisingly, over half of their random insertions resulted in the algae giving off light in a rhythmic pattern. This suggests that the biological clock controls hundreds of genes, and according to one of the researchers, it also indicates that a biological clock's control over life's processes is much more widespread than previously thought.

This research, and other along these lines, has revolutionized the study of plant clock genes. Plants that Mother Nature never intended to glow are lighting up in labs all over, and scientists are one step closer to cracking her master plan for life. These techniques may help researchers determine why biological clocks can be affected by exposure to or deprivation of light. With this new information, we are closer to understanding jet lag, sleeping disorders and diseases like Seasonal Affective Disorder.