Natures wonders: new found plant defenses (Introduction)

by David Turell , Friday, December 07, 2018, 23:17 (2176 days ago) @ David Turell

Another defense found:

https://www.sciencedaily.com/releases/2018/12/181207112727.htm

"Plants wounded by e.g. chewing herbivores produce jasmonic acid as a defense signal, as a phytohormone to mount their defense responses -- this includes for example the formation of toxic substances. They even employ volatile derivatives of jasmonic acid to warn their neighbors to fight the rising threat in time.

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"They found that jasmonic acid also is involved in the quick closure of stomata.

"Stomata are adjustable pores formed by two guard cells in the epidermis of plant leaves. They control the uptake of carbon dioxide crucial for photosynthesis and at the same time the plants' water balance. The phytohormone abscisic acid (ABA) represents a key signal for stomatal closure. Plants produce ABA during drought stress to save water.

"During their experiments on guard cell volume control by biotic stress the team from the JMU Chair of Plantphysiology and Biophysics noticed that mechanical wounding of leaves of the model plant Arabidopsis thaliana quickly triggers stomatal closure, too. Surprisingly, this effect was not restricted to the wounded leaf, but also occurred in neighboring leaves.

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"Stomatal closure requires the efflux of anions and potassium mediated by guard cell ion channels. To understand the molecular mechanism that underlie jasmonic acid controlled stomatal closure the Becker team went out searching for mutants that would not respond to jasmonate treatment.

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"'Wounding induces calcium signals in guard cells and in electrophysiological studies we could demonstrate that the calcium-binding CBL1/CIPK5 complex activates the ion channel," Dirk Becker states.

"The research team further identified the protein phosphatase ABI2 to counteract kinase mediated channel activation, thus representing a negative regulator of jasmonate signaling in guard cells. Becker further explains, "Interestingly, ABI2 is the co-receptor for the plant drought hormone ABA. This is indicating molecular crosstalk between the two phytohormones jasmonic acid and abscisic acid." Indeed, together with colleagues from the Pedro Rodriguez lab (Universitat Politecnica Valencia) the team could show that Arabidopsis mutants lacking guard cell ABA receptors are also insensitive to jasmonic acid.

"With their story the international team of plant biologists led by JMU scientist Dirk Becker has made an important step in understanding the molecular framework that allows plants to respond to wounding stress in guard cells. Leaf turgor and photosynthetic rates correlate with stomatal conductance.

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"Plant pathogenic Pseudomonas bacteria are capable of producing a molecular mimicry of jasmonic acid, known as Coronatine. Plant physiologists commonly use Coronatine as a substitute for jasmonic acid in their experiments.

"'In the long term, however," Becker explains, "Coronatine does just the opposite of jasmonic acid in guard cells: it opens stomata providing an entry pathway for the pathogenic bacteria." This puzzling observation shall be resolved in future studies by comparing differentially expressed genes in guard cells after jasmonic acid or coronatine treatment."

Comment: more plant complexity in their defense mechanisms. How did Pseudomonas bacteria learn to mimic jasmonic acid? Trial and error? Did God bother to design this? At times the findings have no apparent explanation.