Confuse Some Plants Inner Workings
By Dawn Lyons
November 20, 1996
URBANA, Ill., Nov.
20--Chilly nights can mean internal turmoil for warm-weather plants like
tomatoes, soybeans and corn, resulting in reduced yields, U.S. Department of
Agriculture scientists say.
Scientists with USDAs Agricultural Research Service have discovered
that when overnight temperatures dip below 50 degrees Fahrenheit, crucial
biochemical processes that typically occur inside the plant at night may shut
down--only to revive in the next days warmer temperatures and clash with
daytime biochemical activities. The result: less efficient photosynthesis,
slashed yields and a possible explanation for the geographic limits imposed on
plants by their temperature sensitivity.
Plants have an internal timekeeping mechanism called circadian rhythm that
regulates the internal processes over a 24-hour period, explains ARS plant
physiologist Don Ort at the agencys Photosynthesis Research Unit here.
There are specific reactions that are timed to occur at a given period of
day or night, Ort says. If they occur at the same time, they
compete and stall photosynthesis, just as competing foot movement would
paralyze a runner.
For example, temperatures might drop below 50
degrees at 10 p.m., stalling nighttime biochemical processes in a tomato plant.
When the weather warms up again at 8 a.m., the plant may resume its interrupted
nighttime processes. But at the same time, the plants internal clock
kicks off the regularly scheduled daytime biochemical activity, resulting in
competition with the lingering night processes.
ARS scientists have shown that the activity of two critical enzymes, sucrose
phosphate synthase and nitrate reductase, are regulated by a circadian rhythm
that is disrupted by cool temperatures in chill-sensitive plants like tomatoes.
The scientists hope to use this information to override low-temperature
sensitivity in several economically important crops. If we can improve
the plants ability to tolerate lower temperatures, even by one or two
degrees, we would significantly improve the biological efficiency and
productivity of these crops, Ort says.
A report on Orts work is featured in the October issue of
Agricultural Research, the monthly magazine of the Agricultural Research
Service. The magazine is accessible on the World Wide Web in PDF file format
Scientific contact: Donald Ort, Photosynthesis Research Unit,
Agricultural Research Service, USDA, 190 ERML, 1201 W. Gregory Drive, Urbana,
Ill. 61801; phone: (217) 333-2093, email@example.com.