Stomata Open the Door


Next up in the Frozen series… Love may open the door to our hearts, but stomata are the gatekeepers of gas exchange in plants. Here’s the Disney version for your reference.


[Guard Cell1:] Okay, do you feel like we need some CO2?

[Guard Cell2:] I love CO2!

[CO2:] All my life has been just cell walls in my face
And then suddenly I bump into you

[Guard Cell1:]
I was thinking the same thing! ‘Cause like
I’ve been sensing all night, we need some uptake
And maybe it’s the potassium talking or the full vacuole
[Guard Cell2:] [giggles]

[Guard Cell1:] But with you…
[Guard Cell2:] But with you

[Guard Cell1:] I open up…
[Guard Cell2:] I make a space…

And finally those guard cells make a pore!
Stomata, open the door!
Stomata, open the door!
Stomata, open the door!

[Guard Cell1:] With you!
[Guard Cell2:] With you!
[Guard Cell1:] CO2!
[Guard Cell2:] O2 too!
[CO2:] Stomata, open the door…

[Guard Cell1:] I mean it’s crazy…
[Guard Cell2:] What?

[Guard Cell1:] We expose all of the-
[Guard Cell2:] Mesophyll!

[CO2:] That’s what I was gonna say!

[Guard Cell 2:] I’ve never met some cell-

[Guard Cells:]
Who expands so much like me!
Jinx! Jinx again!
Our spatial synchronization
Can have but one explanation

[Guard Cell1:] You-
[Guard Cell2:] And I-
[Guard Cell1:] Were-
[Guard Cell2:] Meant-

[Guard Cells:] Developmentally!

[Guard Cell1:] Say goodbye…
[Guard Cell2:] Say goodbye…

[Guard Cells:]
To the H2O flying past
I think we shouldn’t transpire anymore!

We need to shut this door!
We need to shut this door!
If we want to live much more!

[Guard Cell1:] With you!
[Guard Cell2:] With you!
[Guard Cell1:] Sorry CO2!
[Guard Cell2:] Me too!

[CO2:] Dang it! They shut the door!

[Guard Cell1:] Can I say something crazy?
[Guard Cell2:] [giggles]
[Guard Cell1:] Do this again tomorrow?
[Guard Cell2:] Can I say something even crazier? Yes!


Guard cells, those crazy kids! Am I right? This song only makes them seem fickle. In real life, the motions of the guard cells of the stomata are tightly controlled. They comprise the respiratory system of plants allowing the entry of CO2 and exit of O2 at designated locations on the leaf. Check out this video with excellent illustrations of how these guard cells work together in the plant.

As explained in the video, the opening and closing of stomata must be a tightly controlled process. Plants need to open them up in order to allow for the entry of CO2 and exit of O2. Obviously, this is linked to photosynthetic activity, which increases during the day and ceases at night. Yes, even though those ‘dark’ or light-independent reactions would continue to occur at night, the biggest demand is during the day. Carbon fixation can still occur at night with whatever CO2 reserve remains in the air spaces of the mesophyll layer of the leaf. Stomatal opening is also controlled by CO2 concentration in the atmosphere. When CO2 concentrations are low, more stomata must be opened for longer periods to take in the necessary amount. In the case of increased atmospheric CO2 concentrations, the opposite is true, and plants can leave more of their stomata closed.

All of this gas exchange comes at the expense of water; water loss is the price plants pay for increased access to CO2. During a typical day, the demand for CO2 at night doesn’t justify the water-cost of having the stomata open. When water is at a premium, other signals can override stomatal opening even during the day. For example, the plant hormone ABA is produced at the onset of drought conditions and guard cells respond to this molecule by closing the stomata.

Given that the open/closed state of stomata is dependent on so many environmental factors, guard cells must have systems for integrating many combinations of molecular signals. Guard cells must be able to sense and respond to light, CO2 concentration, plant hormones like ABA, as well as the overall photosynthetic productivity of mesophyll cells. This means that have sophisticated regulatory networks that sort out all of these signals. The exact details of how this works are active areas of research by plant scientists.

Scientists have unraveled many details regarding how exactly guard cells change their shape to create the open or closed states. The path to opening the stomatal door hinges on the activity of an ATPase proton pump at the plasma membrane of the guard cells. This moves H+ ions out of the guard cells. The resulting proton gradient triggers the opening of a gated K+ channel to move K+ ions into the cell in an attempt to keep the appropriate charge balance across the membrane. This movement of positively charged ions also causes the redistribution of negatively charged ions like Cland malate into the guard cells. This change in ion distribution as well as the relative concentrations of sugars within the cell drives the movement of water into the guard cells by osmosis. The increased turgor pressure from the influx of water causes the guard cells to take on the kidney shape which opens the stoma. Signals that trigger the closing of the stoma reverse these ionic distributions, causing the cells to lose water, become flaccid and close the aperture of the stoma.

Finally, stomata are not only interesting to plant scientists. Plant pathogens have long since noticed these openings to interior plant tissue, and have come up with ways to exploit this interest for their own sinister purposes. The fungus Fusicoccum amygdali produces the toxin fusicoccin which activates the proton ATPase pump, in turn causing stomata to irreversibly open. This strategy creates access points for fungal hyphae invasion and ultimately plant death from infection and wilting caused by the constant loss of water through open stomata. Thus, even in the plant world it’s deadly to be betrayed from within by a signal that should have been simpler to interpret.




References and Links:


3 thoughts on “Stomata Open the Door

  1. Pingback: Frozen: A Plant Science Parody | New Under The Sun Blog

  2. sarahjose

    I’ve just played the song and sung along. 😀 I sent it to my entire lab this afternoon and I’m thinking we need to have a lab singalong in the near future!

    Every time I see a closed stoma I’ll feel bad for the CO2 now though!


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