When I was an undergraduate, one of my favorite courses was a seminar in biological clocks and circadian rhythms taught by Hugh Wilcox at Syracuse. Biological clocks have fascinated biologists since the 19th century, but until recently it was not possible to look at the mechanisms underlying daily variation in behavior. With the advent of molecular biology, it is now possible to look directly at genes expressed at various times of day. The trick is to separate gene expression that is cued by an external signal, like sunrise, from gene expression cued by an organisms internal clock.
Charles Darwin was probably the first to recognize that plants vary through the day and night in the rate of growth and movement. Most often, plants grow more at night than during the day.
Using DNA microarrays, Todd Michael and his colleagues have found that a group of genes related to expression of plant growth regulators in Arabidopsis are at a maximum during the night and are associated with a growth spurt just before dawn. The peak in gene expression was associated with expression of phytohormone regulatory elements. It appears that peaks in growth during the night are related to circadian variation in expression of regulatory elements with external cues (light and dark periods) setting the clock.
This research contributes to our rapidly increasing body of knowledge about how plants regulate themselves and optimize their use of resources throughout the day-night cycle.
Citation:
Michael TP, Breton G, Hazen SP, Priest H, Mockler TC, et al. 2008 A Morning-Specific Phytohormone Gene Expression Program underlying Rhythmic Plant Growth PLoS Biology Vol. 6, No. 9, e225 doi:10.1371/journal.pbio.0060225
Links:
