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 Post subject: Touchy Plants
PostPosted: Sat 21. Apr 2012, 03:18 
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From: Editor, ENN
Published April 11, 2012 04:20 PM



Touchy Plants



Plants just sit and grow. They do not see, smell or touch or do they? A new study by Rice University scientists reveals that plants can use the sense of touch to fight off fungal infections and insects. The study, which will be published in the April 24 issue of Current Biology, finds that plant defenses are enhanced when plants are touched. Rice University biologists found that plant defenses against leaf-eating herbivores, like this cabbage looper caterpillar, are activated by the plant's sense of touch. "From previous studies, we knew that plants change their growth in response to touch but we didn’t know how these growth changes were activated," said Wassim Chehab, a faculty fellow in Rice’s Department of Biochemistry and Cell Biology and lead author of the new study. "We used a widely studied plant, Arabidopsis thaliana, to test the idea that the touch-induced growth was regulated by a plant hormone called jasmonate."

In the study of plant physiology plant perception is a term used to describe mechanisms by which plants recognize changes in the environment.
Examples of stimuli which plants perceive and can react to include chemicals, gravity, light, moisture, infections, temperature, oxygen and carbon dioxide concentrations, parasite infestation, physical disruption, and touch. Plants have a variety of means to detect such stimuli and a variety of reaction responses or behaviors.

These responses are generally slow, taking a number of hours to accomplish, and can best be observed with time-lapse cinematography, but rapid movements can occur as well.

Jasmonate plays a critical role in initiating plant defenses against plant-eating insects. When jasmonate levels go up, the plant increases production of metabolites that give herbivores an upset stomach. Jasmonate defenses, which also protect against some fungal infections, are employed by virtually all plants, including tomatoes, rice and corn. The new study provides the first evidence that these defenses are triggered when plants are touched. In the study, students touched the plants in a laboratory, but the researchers say the touch-induced response could also be activated by animals, including insects, and wind.

“Plants can’t move, so it makes sense for them to have a highly developed sense of touch to react quickly to changes in their environment,”� said study co-author Janet Braam, professor and chair of Rice’s Department of Biochemistry and Cell Biology.

The famed Venus flytrap uses its sense of touch to rapidly close and trap insects. But in prior research at Rice, Braam and her colleagues showed that Arabidopsis was also extremely responsive to touch. In 2000, her lab used tools of biotechnology to produce a plant that glowed with light wherever it was touched. They also showed that Arabidopsis plants that were touched regularly grew much shorter and slower — much like trees exposed to a windy coastline will grow short and bent.

Braam said. “Our experiments show that plants that are repeatedly touched maintain high levels of jasmonate and therefore have enhanced insect and fungal tolerance. In addition, we found that eliminating key genes required for jasmonate production results in the inability of plants to grow shorter and slower when touched.”�
Wassim Chehab and Janet Braam

“There are multiple signals that can influence the jasmonate response,”� Chehab said. “Touch is one, but we also recently found that this response can be mediated by the plant’s internal clock, or circadian rhythm. It’s a complicated picture, but by piecing it together, we get a clearer understanding of plant pest resistance.”�

Further information at Rice University


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