CO2 regulates stomata opening
Stomata, the pores on the underside of the leaf, let CO2 in for photosynthesis and water vapour out. Regulation of these openings is of great importance for the plant. Are these pores open too long during hot dry days, then a plant loses lots of water, but when they are close there can be no photosynthesis and the plant starves. Now researchers show that by an increasing of CO2 in the atmosphere plants are not using this to fix more energy but for saving water.
The closing and opening of the stomata goes accompanied by an increase or decrease of the internal pressure in the guard cells of stomata. the cell regulates this by pumping potassium ions in or out of the cell. This in turn activates the process of osmosis, the movement of water from one side of the membrane to the other side in order to keep the ion concentration – in this case potassium ions – on both sides of the membrane as equal as possible. Extra water in the guard cells of the stomata allows them to swell and close the pore. Less water has the opposite effect.
Less potassium pumps
Through adding a fluorescent tag to the potassium pump KAT1 the researchers noticed that by an increase of CO2 there are less KAT1 potassium pumps in the membrane. To check if the cell actively removes those potassium pumps the researchers used a locally deactivated the tag. Under normal CO2 levels no new signal appeared, but at higher CO2 levels a new signal was quickly observed. The only way a new signal could appear that quickly was by placing a new potassium pump with an active tag into that area.
For removing and placing proteins in the cell membrane the cell uses a system called SNARE. The proteins of the SNARE system are able to create a small membrane bubble using the membrane around the protein that they want to remove, in such a way that the to removed protein is part of that newly formed membrane bubble. The SNARE system can also intergrade those membrane bubbles into the cell membrane.
SYP121 is one of the proteins of the SNARE-system that recognises proteins that the cell wants to remove from the membrane. The researchers checked if SYP121 also recognises KAT1 by an increase of CO2. In plants without SYP121 the potassium pump KAT1 remained in the cell membrane by an increase of CO2.
Efficient water use
The researchers expected that by an increase of CO2 more SYP121 would bind to KAT1. But when they checked this, they found that the opposite occurred. This suggest that not the binding of SYP121 to KAT1, but the not binding of SYP121 to KAT1 signals that KAT1 needs to be removed by the SNARE-system.
Lastly the researchers analysed the effect that of the removal of the potassium pump has on plants growing under increase CO2 levels. Plants without SYP121, who can’t adjust the numbers of their potassium pumps in response to CO2, appeared to grow less at higher CO2 levels. These plants also closed and opened their stomata slower than plants with SYP121. In addition, plants without SYP121 had a lower water use efficiency.
Al together this study shows that the stomata of plants react to the amount of CO2 in the air. Not as much as to increase the amount of CO2 that they take up, but to limit the amount of water that evaporates.
Literature
Yu, Z., Waghmare, S., Farami, S., Blatt, M.R., and Karnik, R. (2026). CO2-sensitive K+ channel traffic affects stomata and whole-plant water use. J. Integr. Plant Biol.00: 1–18. https://onlinelibrary.wiley.com/doi/10.1111/jipb.70269
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