How did a herbicide make a better weed?
By Chelsie Vandaveer
August 7, 2003
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Common groundsel (Senecio vulgaris Linnaeus) is an annual native to Eurasia. It grows during cool weather. Where winters are mild, groundsel will flower through the winter months; where summers are cool, groundsel will survive as a biennial. The plant is a nuisance in pasture land especially when established in crops like alfalfa used for hay. Whether fresh or dried, groundsel causes liver damage in cattle and horses.
A member of the Asteraceae, groundsel produces an inflorescence, a head of disk florets (greatly reduced flowers). The flowers are self-fertile; each produces a single seed within an achene (a hard dry fruit). The achene is attached to a pappus of feathery bristles designed to carry the seed on the wind. If conditions are good and nothing interrupts the groundsel's life cycle, it can produce up to a million seeds before it dies. ("Common Groundsel, Senecio vulgaris L.", Susan Aldrich-Markham, Weeds, Pacific Northwest Extension Publication, 1994)
Groundsel was controlled by spraying the plants with the herbicide, atrazine. Atrazine is taken up through the roots, transported through the plant, and attaches to the membrane of the chloroplast where photosynthesis takes place. The atrazine molecule replaces a quinone, an electron carrier molecule, but atrazine does not transport electrons.
The energy collected from sunlight is 'short-circuited'; it never gets to the location where the energy is stored as chemical energy in a sugar molecule. The plant starves. ("Applying the Tools of Biotechnology to Agricultural Problems", Genetic Engineering of Plants: Agricultural Research Opportunities and Policy Concerns, 1984, NAP, National Academy of Sciences)
In all the millions of seeds, some groundsels were mutated to an atrazine-resistant variety. The mutation was in a protein of the membrane of the chloroplast. A quinone molecule will still bind to the membrane, but an atrazine molecule will not. Atrazine-resistant groundsel is not as efficient at photosynthesis as its nonresistant variety. It takes longer to grow and flower, but the plants will not be on the endangered species list anytime soon.
Missouri Flora has photographs of common groundsel taken by Dan Tenaglia. To view the photographs, click on the link:
http://www.missouriplants.com/Yellowalt/Senecio_vulgaris_page.html
Series: | 1 | | 2 | | 3 |
killerPlants Tendrils: ~~1~~2~~3~~4~~5~~
Suggested Reading:
What is groundsel? Herbal Folklore - August 4, 2003
Why was it called an old man? What's in a Name? - August 8, 2003
What weed was a treatment for mange? Herbal Folklore - January 5, 2004
What was spirit weed? Herbal Folklore - October 11, 2004
What common weed is called a poorman's weatherglass? What's in a Name? - October 26, 2001
What is the withywind? Weird Plants - November 7, 2002
What lawn weed was once a tonic? Herbal Folklore - January 28, 2002
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