Scientists discover energetics behind plant breathing (guard cell and stomata)

In the morning, sunlight triggers stomata, which are tiny pores on plant leaves, to open. This let carbon dioxide in and oxygen out to boost photosynthesis. The opening of stomata consumes a large amount of adenosine triphosphate (ATP), the cellular energy currency, but the sources of ATP for stomata opening remained obscure.
Now researchers shows that guard cells (GCs) photosynthesis is poorly active. Sugars synthesised and supplied by mesophyll cells (MCs) are imported into GCs and consumed by mitochondria to generate ATP for stomatal opening. Guard cell chloroplasts (GCCs) take up cytosolic ATP via the nucleotide transporters (NTTs) on chloroplast membrane to energise starch synthesis in daytime. At dawn, while MCs start to synthesise starch and export sucrose, GCs degrade starch into sugars to supply energy and increase turgor pressure for stomatal opening. Hence, the function of GCCs to serve as a store of starch is important for stomatal opening. While MCs fix CO2 in chloroplasts via the Calvin–Benson–Bassham (CBB) cycle, anaplerotic CO2 fixation in the cytosol is the main pathway of CO2 assimilation in GCs, where the downstream product malate, is also an important solute to increase turgor pressure for stomatal opening. In conclusion, GCs behave more like a sink (receive sugars) than a source (provide sugars) tissue (e.g. MCs). Their function is tightly correlated with that of MCs to efficiently coordinate CO2 uptake via stomata and CO2 fixation in MCs. The findings were recently published in the journal Nature Communications.
Shey-Li Lim, Sabrina Flütsch, Jinhong Liu, Luca Distefano, Diana Santelia, Boon Leong Lim (2022) Arabidopsis guard cell chloroplasts import cytosolic ATP for starch turnover and stomatal opening. Nature Communications.