New research adds insight into how plants breathe

Through photosynthesis plants convert carbon dioxide from the atmosphere into glucose and oxygen, it just takes a little water and sunlight.

It’s often referred to as: “breathing in” carbon dioxide (CO2) and “breathing out” oxygen (O2), and the process occurs in stomata on the surface of the leaves.

Stomata are like minuscule mouths which open and close to control the amount of gas being exchanged between the plant and the atmosphere. This is essential for regulating photosynthesis and water use, as plants lose water through stomata too.

It’s no surprise then that the opening and closing of stomata isn’t random. And researchers have now discovered the molecular mechanism that occurs inside plant cells to regulate these rhythmic stomata movements throughout the day. 

The new study is published in Nature Communications.

Stomata are each made up of 2 paired guard cells with a pore in between. Plants increase or decrease the size of this opening by swelling or shrinking the guard cells, respectively.

They do this by pumping ions into and out of the cells, hence causing water to diffuse into or out of the cells due to osmosis.

Both external environmental and internal factors determine to what extent the stomata open and when. In general stomata close to prevent water loss at night and during conditions of water stress, in response to the stress hormone abscisic acid (ABA). Sunlight then induces them to open during the day.

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Credit: CRAG

Researchers studied the model plant Arabidopsis thaliana in periods of controlled light and dark to identify the proteins and genes involved in this process.

They found that a family of proteins named Phytochrome Interacting Factors, or PIFs, accumulate at the end of the night period to induce stomata opening in the morning.

PIFs are transcription factors – proteins that control the expression of genes. They found that the accumulation of PIFs triggers the expression of the KAT1 gene, a guard cell-specific potassium (K+) channel.

In the morning the presence of light activates the KAT1 protein, which triggers the intake of potassium ions and the swelling of guard cells, therefore causing stomata to open. Light also induces the breakdown of PIFs to make sure that KAT1 isn’t expressed throughout the day.

The authors think that under stress conditions, such as low humidity or drought, accumulation of the stress hormone ABA could override this PIF-mediated signal by repressing KAT1 expression to prevent stomata opening in the morning and preserve water.

“How ABA might repress PIF-mediated induction of KAT1 is currently unknown,” they write.

“Correct timing and speed of stomatal movements through the day/night cycle is critical for optimised carbon uptake, photosynthesis, water use efficiency, and control of plant physiology.

“Therefore, understanding how the day/night cycle regulates stomatal movements can provide targets to optimise plant yield with improved water use.”

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