Time was, only the most spiritually inclined believed that plants cry out when they’re in trouble. Last February, though, biochemist Ilya Raskin and his colleagues at Rutgers University published a paper suggesting that they think so, too. The tobacco plants they studied signal their distress not with sound but with a chemical—salicylic acid, or aspirin.
Researchers first found salicylic acid a century ago in willow bark, and many plants seem to produce the chemical. But it was not until six years ago that Raskin and other researchers discovered that plants use the acid to alert their immune system to start fighting infection. This past year, Raskin found that the aspirin can also take to the air—not only activating an immune response in the plant that produced it but switching on the resistance of nearby plants. This is the first case, says Raskin, of plants communicating to fend off disease. Plants can’t run away, and they can’t make noises or sounds, he says. But they are wonderful chemists.
Raskin studied tobacco plants infected with tobacco mosaic virus, which forms dark blisters on leaves and causes them to pucker and yellow. The sick plants produce salicylic acid in large quantities. He and his colleagues found that some of the acid turns into methyl salicylate, a volatile chemical that evaporates from diseased parts of plants. When the researchers pumped air from infected tobacco plants over healthy ones, the healthy plants absorbed the methyl salicylate and turned it back into salicylic acid. That triggered the production of immune-system proteins, making the healthy plants more resistant to the disease. On the other hand, when the researchers removed the methyl salicylate first, the rest of the air caused no increase in the healthy plants’ immunity.
Raskin sees crops one day being treated with aspirin instead of pesticides. In the case of fruits and vegetables, which are still alive long after their harvest, salicylic acid could even help them resist disease while they are being stored. Instead of spraying toxic chemicals and poisons to kill pathogens, Raskin says, this is supplying the plants with a natural substance to boost their own immunity.