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Phoenix666 [soylentnews.org] writes:

Compared to the hectic rush of our bipedal world, a plant’s life may appear an oasis of tranquility. But look a little closer. The voracious appetites of pests put plants under constant stress: They have to fight just to stay alive.

And fight they do. Far from being passive victims, plants have evolved potent defenses [nautil.us]: chemical compounds that serve as toxins, signal an escalating attack, and solicit help from unlikely allies.

However, all of this security comes at a cost: energy and other resources that plants could otherwise use for growth and repair. So to balance the budget, plants have to be selective about how and when to deploy their chemical arsenal. Here are five tactics they’ve developed to ward off their insect foes without sacrificing their own wellbeing.

Warning Flares

Rather than pump out chemical defenses 24-7 (a waste of resources), plants hold off production until an attack is underway. As soon as an insect bites a leaf, the leaf sounds the alarm by emitting volatiles—chemical flares that tell other parts of the plant, as well as its neighbors, to start manning the barricades.
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Calls for Backup

Plants also conserve resources by recruiting allies to fight some of their battles for them. Among a plant’s armaments are volatiles that beckon predators of its insect attackers.
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Booby Traps

Why go to the trouble of firing weapons willy-nilly when you can lure your attacker into a carefully set trap? Plants in the Brassicaceae family (including broccoli, cabbage, and mustard) store seemingly harmless compounds known as glucosinolates in cellular compartments next to stores of enzymes called myrosinase. The two reserves are separated only by a thin cell wall. When an unsuspecting herbivore chews through this wall, the myrosinase enzymes mix with the glucosinolates, catalyzing chemical reactions that engulf the attacker in a toxic cloud. (It’s these reactions that give Brassicaceae species their characteristic bitter flavors and antioxidant properties.)
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Spy Games

Some plants have learned the communication codes of their enemies and use them to spread false information. Aphids, for example, release the pheromone β-farnesene when a predator attacks. This warning tells other aphids in the area that they’ve been rumbled and it’s time to skedaddle. Plants often emit β-farnesene during an aphid attack, perhaps in an attempt to scare off their aggressors by aping their distress call. But not just any β-farnesene signal will do.
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Emergency First Aid

During a hard-fought battle, a plant must tend to its injuries. A range of compounds known as green leaf volatiles act as antiseptics, protecting damaged tissue against bacterial or fungal infection. (These volatiles, which make up the fragrance of freshly cut grass, send another warning to neighboring plants, reminding them that danger is at hand.)

The war metaphor is overwrought, but the article adds an interesting dimension to the plants around us.

Original Submission