In a realm imperceptible to the human eye, plants envelop themselves in a delicate mist of airborne compounds, employing this ethereal language for communication and self-defense. Comparable to scents, these compounds serve to repel hungry herbivores and alert neighboring plants to impending threats. While scientists have recognized these plant defense mechanisms since the 1980s, the process of how plants receive and respond to these aerial alarms has remained a significant gap in our understanding.

Addressing this knowledge gap, a team of Japanese researchers, led by molecular biologists Yuri Aratani and Takuya Uemura from Saitama University, utilized real-time imaging techniques to unravel the mysteries of plant communication. The researchers conducted experiments involving the transfer of compounds emitted by injured and insect-infested plants onto undamaged counterparts, observing the responses using a fluorescence microscope.

Leaves from tomato plants and Arabidopsis thaliana, a common mustard family weed, were subjected to caterpillar attacks (Spodoptera litura). The researchers, having genetically modified these plants with a biosensor that fluoresces green upon detecting an influx of calcium ions, monitored the responses of intact Arabidopsis plants to the danger cues.

The study revealed that volatile compounds released by wounded plants induce calcium signals in Arabidopsis. Two specific compounds, Z-3-HAL and E-2-HAL, were identified as key contributors to this response. The researchers further determined that guard cells, which form stomata on plant surfaces, play a crucial role in initiating the response. Stomata, akin to the plant’s ‘nostrils,’ act as gatekeepers, responding to the airborne compounds and subsequently triggering calcium signals in mesophyll cells—the inner tissue of leaves.

By engineering fluorescent sensors exclusively in guard, mesophyll, or epidermal cells, the researchers pinpointed the precise cells that first respond to the danger cues. The orchestrated response sequence, where guard cells generate calcium signals followed by mesophyll cells, provided a detailed understanding of how plants react to airborne warnings.

In essence, this groundbreaking study, led by senior author Masatsugu Toyota, has unveiled the intricate story of when, where, and how plants decode and respond to the subtle ‘warning messages’ wafting through the air from their distressed neighbors.

By Impact Lab