Plants growing close together can warn one another about environmental stress, helping their neighbours survive conditions that would otherwise cause serious damage.
In experiments with thale cress (Arabidopsis thaliana), researchers grew plants either in isolation or packed so closely that their leaves touched. When exposed to intense light, isolated plants suffered severe damage, while crowded plants coped much better by rapidly activating their defences.
Within just one hour, densely grown plants switched on more than 2,000 genes involved in protection against a wide range of stresses. Isolated plants showed little additional gene activity, indicating they were unable to mount the same response.
The findings suggest that stressed plants send warning signals to nearby neighbours. The study showed that crowded plants released hydrogen peroxide, a molecule known to trigger defensive responses. Crucially, this is the first evidence that hydrogen peroxide can pass from one plant to another, acting as an alarm signal that prepares surrounding plants for incoming stress.
