An amaz­ing re­ac­tion hap­pens when a plant gets hurt, new re­search finds

Tehran Times - - SCIENCE -

When plants are un­der attack - say, for in­stance, by an in­sect mak­ing a tasty leaf meal - their de­fense sys­tems are raised in other parts. How do they know to do that?

Ac­cord­ing to new re­search, plants use the same sig­nal­ing mol­e­cules that an­i­mals use in their ner­vous sys­tem. Our green friends don’t have nerves, ex­actly - but they cer­tainly have some­thing sur­pris­ingly sim­i­lar.

The re­search in­volved us­ing flu­o­res­cent pro­teins to mark and watch the sig­nals as they travel in waves through plants in re­sponse to a stres­sor.

“We know there’s this sys­temic sig­nal­ing sys­tem, and if you wound in one place the rest of the plant trig­gers its de­fense re­sponses. But we didn’t know what was be­hind this sys­tem,” ex­plained botanist Si­mon Gil­roy from the Univer­sity of Wis­con­sin-Madi­son.

An elec­tri­cal charge fires

What they did know is that if a plant gets wounded, an elec­tri­cal charge fires, prop­a­gat­ing across the plant. The un­known part was what trig­gered that charge and helped prop­a­gate it - but that’s not even what the re­searchers were try­ing to study.

What they were orig­i­nally look­ing at was how plants re­spond to grav­ity by study­ing in­creases in cal­cium. So botanist Masat­sugu Toy­ota ge­net­i­cally en­gi­neered a mus­tard plant that would let the re­searchers ob­serve changes in cal­cium con­cen­tra­tion in real-time.

He in­tro­duced a pro­tein that only flu­o­resces in the pres­ence of cal­cium. And then the re­searchers cut a leaf to see if they could de­tect cal­cium changes.

In an­i­mals, an ex­cited nerve cell re­leases an amino acid called glu­ta­mate, which trig­gers a wave of elec­tri­cally charged cal­cium ions that prop­a­gate to cells far­ther and far­ther away from the site.

As you can see from the videos, what hap­pened to the plants is noth­ing short of in­cred­i­ble. Waves of light flow out from the source of the wound, spread­ing through the plant at the speed of about a mil­lime­ter per sec­ond.

It’s a lot slower than an­i­mal nerve sig­nals, which can travel up to 120 me­ters per sec­ond (268 mph), but for plants this is su­per speedy com­mu­ni­ca­tion.

De­fen­sive hor­mones

The re­searchers dis­cov­ered that once the wave hits, de­fen­sive hor­mones rise in that re­gion of the plant.

This tells the plant to mount its de­fenses, such as an in­crease in nox­ious chem­i­cals that will make the plant un­palat­able to munch­ing in­sects, or as is known in the case of grass - the re­lease of smelly volatiles that sig­nal par­a­sitic wasps to come and lay their eggs in in­sects that might be eat­ing it.

But what was trig­ger­ing the cal­cium waves? Just like in an­i­mals, the re­searchers be­lieved it might be glu­ta­mate, which is also found in plants. And pre­vi­ous re­search pub­lished in 2013 re­vealed that plants miss­ing glu­ta­mate re­cep­tors also did not have an elec­tri­cal threat re­sponse.

So the re­search team wounded plants with­out glu­ta­mate re­cep­tors to see if there was an ef­fect on cal­cium flow.

“Lo and be­hold, the mu­tants that knock out the elec­tri­cal sig­nal­ing com­pletely knock out the cal­cium sig­nal­ing as well,” Gil­roy said.

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