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Plants have microscopic pores on the surface of their leaves, the stomata. With their help, they regulate the influx of carbon dioxide for photosynthesis. They also use the stomata to prevent too much water loss and dieback during drought.
The stomatal pores are surrounded by two guard cells. If the internal pressure of these cells drops, they relax and close the pore. If the pressure increases, the cells separate and the pore widens.
Stomatal movements are thus regulated by the guard cells. The signaling pathways in these cells are so complex that it is difficult for humans to intervene directly with them. However, researchers at Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, have nonetheless found a way to control stoma movements from a distance – using light pulses.
Photosensitive algae proteins used
The researchers managed to do this by introducing a light-sensitive switch into the guard cells of the tobacco plants. This technology comes from optogenetics. It has been successfully exploited in animal cells, but its application in plant cells is still in its infancy.
The team led by biophysicist JMU and expert in guard cells, Professor Rainer Hedrich, describes their approach in the prestigious scientific journal Scientists progress. JMU researchers Shouguang Huang (first author), Kai Konrad and Rob Roelfsema were significantly involved.
The group used a light-sensitive protein from the alga Guillardia theta as a light switch, namely the anion channel ACR1 of the rhodopsin group. In response to the light pulses, the switch ensures that the chloride flows out of the guard cells and that the potassium follows. The guard cells lose their internal pressure, relax and the pore closes in 15 minutes. “The light pulse is like a remote control for the movement of the stomata,” Hedrich explains.
Anion channel hypothesis confirmed
“By exposing ACR1 to light, we bridged the cell’s own signaling chain, proving the hypothesis that opening anion channels is essential and sufficient for stomata closure,” summarizes Hedrich’s findings. study. Exposure to light had almost completely prevented transpiration of the plants.
With this knowledge, it is now possible to cultivate plants with an increased number of anion channels in guard cells. Plants thus equipped should close their stomata more quickly in the face of approaching heat waves and thus better cope with periods of drought.
“The anion channels in plants are activated during stress; this process depends on calcium. In a follow-up optogenetics project, we want to use calcium-conducting channelrhodopsins to specifically allow calcium to flow into the guard cell upon exposure to light and to understand the mechanism of anion channel activation in detail ” , Hedrich describes the future goals of his research.
Basic scientific research can also benefit from the results of Würzburg: “Our new optogenetic tool has enormous potential for research,” says Professor JMU. “With this, we can gain new knowledge about how plants regulate their water intake and how carbon dioxide uptake and stomatal movements are coupled.”
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