Light-Emitting Nanosensors Track Chemical Signals in Plants

An international research team led by Tedrick Lew and Michael Strano at the Massachusetts Institute of Technology have created a new device for observing variations in waves of hydrogen peroxide as they pass through the tissues of different species of plant. The team said its approach represents an important step forward for the integration of nanotechnology and plant science and could have numerous benefits for agriculture.

Recent studies have shown that when plants are damaged, their cells that surround the wound sites release hydrogen peroxide. This triggers the release of calcium ions in neighboring cells and these ions stimulate the release of more hydrogen peroxide. The result is a chemical wave that propagates throughout the plant. Through this communication system, plant cells are instructed to produce the molecules required to repair the damage. Until now there has been no way for biologists to reliably observe how these waves propagate in real time.

Lew, Strano, and colleagues observed these intricate waveforms using a technique first developed by Strano. The team integrated plant tissues with specialized carbon nanotubes that emit near-infrared light specifically on contact with hydrogen peroxide, which can then be imaged directly with an inexpensive camera. The research team found that these nanobionic plants allow the team to map the time-varying concentrations of hydrogen peroxide throughout entire plants.

The researchers also found that their nanosensors could be integrated harmlessly into a diverse range of plants. This allowed them to investigate hydrogen peroxide propagation in six different plant species including lettuce, spinach, and strawberries, without the need for genetic manipulation. They observed the waves traveling at speeds in the range 0.4 to 3.1 m/s, depending on the species. In addition, information about the different types of stress causing the damage, including infection, heat, and mechanical injury, were encoded into the shapes of the waves.

The researchers believe the technology could have numerous applications in agriculture, potentially enabling farmers to screen their crops for their ability to resist damage from factors like water shortages and extreme heat. It could also lead to studies of how certain crops respond to pathogens that are currently unleashing significant damages, including citrus greening and coffee rust. The team said it now has plans for future research; through further upgrades to their nanosensors, the researchers hope to investigate how signals propagate at cellular levels and to decipher their complex dynamics in more detail.

The study was first described in the journal Nature Plants (www.doi.org/10.1038/s41477-020-0632-4).