MadSci Network: Botany
Query:

Re: Why do daisies close their petals at night?

Date: Fri Mar 26 17:51:50 1999
Posted By: Hurley Shepherd, Agricultural Research, USDA Southern Regional Center
Area of science: Botany
ID: 921963157.Bt
Message:

The closing of some species of flowers at night has been seen for hundreds of years, but no one knows the precise reason. One idea is that it conserves the attractant chemicals of the flower from being released at night when there are no pollinators around. In this way the plant doesn't waste its resources.

The same thing happens to leaves of many plants, also. This closing of flowers or leaves is called "nyctinastic" which means "night closing". These processes are controlled by a timing mechanism inside the plant, not by the sun going down and coming up. This is called a "circadian rhythm" because it happens about once every 24 hours (circadian means "about one day"). You can tell it is a circadian rhythm by putting the plant in constant light or dark, and the closing and opening will still happen at about the same time as those left in day and night conditions. You can try this yourself! (Be aware that the rhythm will only last a few days, because the plant needs light to keep the clock going.)

You might find more by searching under "nyctinastic" or "circadian". You'll find that people have circadian rhythms, too.

For a good introduction to nyctinastic movement and some experiments, try:

http://bioclox.bot.biologie.uni-tuebingen.de/Html_we/Buch/current/node93.ht ml

To visit a laboratory site of scientists who are working on circadian rhythms in plants, go to: http://www.lifesci.ucla.edu/mcdbio/Faculty/E.Tobin/lab/labhomepage/newresearchpa ge.html


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