Science Advances: Plants can also be "remotely controlled"

Posted by Ilsa Miller on August 4th, 2021

Plants have very small stomata on their leaf surfaces, i.e., stomata. With their help, they regulate the influx of carbon dioxide in photosynthesis. They also use stomata to prevent water shortage and wilting during drought.

There are two guard cells around the stomata. If the internal pressure of these cells drops, they relax and close the pores. If the pressure increases, the cells separate and the pores widen.

Thus, stomatal movement is regulated by guard cells. The signaling pathways in these cells are very complex and humans intervene directly in them. However, researchers at Julius-Maximilians-Universität of Würzburg have discovered a way to remotely control stomatal movement—using light pulses.

Photoproteins extracted from algae

The researchers successfully did this by introducing a photosensitive switch in the protective cells of tobacco plants. This technique is derived from optogenetics. It has been successfully applied to animal cells, but its application in plant cells is still in its infancy.

A team led by Professor Rainer Hedrich, a JMU biophysicist and expert in protective cells, described their approach in Science Progress. JMU researchers Shouguang Huang (first author), Kai Konrad, and Rob Roelfsema participated.

The team used a photosensitive protein from the alga Guillardia theta as a photoswitch, the anion channel ACR1 from the channel rhodopsin group. In response to light pulses, this switch ensures that chloride ions flow out of guard cells, followed by potassium ions. The guard cells lose internal pressure, relax, and the pores close within 15 min. “The light pulse is like a remote control of stomatal movement,” Hedrich said.

Confirmed the negative channel hypothesis

"By exposing ACR1 to light, we have bridged the cell's own signaling chain, thus demonstrating the hypothesis that opening of anion channels is necessary and sufficient for stomatal closure," Hedrich summarized the results of this study. Exposure to sunlight almost completely prevented transpiration in plants.

With this knowledge, more anion channels can now be cultured in the guard cells of plants. Plants grown in this way can close stomata more quickly in response to upcoming heat waves and thus better cope with periods of drought.

“Anion channels in plants are activated under stress; this process depends on calcium. In a subsequent optogenetic project, we wanted to use the calcium-conducting channel rhodopsin, specifically allowing calcium to flow into guard cells by exposure to light and to understand in detail the mechanism of anion channel activation,” Hedrich outlined his future research goals.

Basic science research can also benefit from the results of Würzburg: “Our new optogenetic tool has great research potential," said Professor JMU. “With it, we can have new insights into how plants regulate their water consumption and how carbon dioxide fixation and stomatal movement are coupled.”

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