How guard cell chloroplasts gain energy

Figure 1: Staining of NTT transporter (blue, left panel) and starch granules (yellow, right panel) with GC.Credit: University of Hong Kong

Whether guard cells (GCs) perform photosynthesis has been debated for decades.Previous studies have suggested that guard cell chloroplasts (GCC) cannot fix CO.2 However, subsequent studies argued that this was not the case. Until recently, it was controversial whether GCC and / or GC photosynthesis played a direct role in stomatal movement. Dr. Boon Leong LIM, an associate professor of bioscience at the University of Hong Kong (HKU), worked with Dr. Diana SANTELIA from ETH Zurich to discover and unravel the true fuel source for GC.The findings were recently published in a prestigious journal Nature Communications..

In the morning, sunlight opens the stomata, which are the small pores of the leaves of the plant. This is CO2 And O2 To promote photosynthesis. The stomatal openings consume large amounts of the cellular energy currency, adenosine triphosphate (ATP), but the source of ATP in the stomatal openings remains unknown. Several studies suggest that GCC performs photosynthesis and exports ATP to the cytosol to energize the stomatal openings.In mesophyllochloroplasts, ATP and NADPH (nicotinamide-adenine dinucleotide phosphate) are produced from the optical system used as a fuel to immobilize CO.2..

By adopting the Planter Fluorescent Protein Sensor, HKU’s team of Dr. Boone Leonlim can visualize the real-time production of ATP and NADPH in the model plant Arabidopsis chloroplast cell chloroplast (MCC). I did. “But GCC was unable to detect the production of ATP or NADPH during illumination. I was confused by this unexpected observation and turned to Dr. Diana Santeria of ETH Zurich, an expert in guard cell metabolism. “Dr. Lim said.In the last 10 years, Santelia Lab has been starching Glucose metabolism In the guard cells (GC) surrounding the stomata on the surface of the leaf.

How guard cell chloroplasts gain energy

Figure 2: Model of coordination between starch and malic acid metabolism and stomatal function in guard cells.Credit: University of Hong Kong

In a collaborative effort, the team has shown that unlike mesophyll cells (MC), GC photosynthesis is less active. The sugars synthesized and supplied by MC are imported into the GC and consumed by mitochondria to produce ATP at the stomatal opening. Unlike MCC, GCC takes up cytosolic ATP via a nucleotide transporter (NTT) on the chloroplast membrane and activates starch synthesis during the day. At dawn, while MC begins to synthesize starch and export sucrose, GC breaks down starch into sugar to provide energy and increase turgor pressure to open pores. Therefore, the function of GCC, which acts as a reservoir for starch, is important for stomatal openings. While MC is modifying CO2 Calvin-Benson-Bassham (CBB) cycle, with chloroplasts via CO2 Fixation in the cytosol is the main pathway for CO2 Assimilation in GC, where the downstream product malate is present, is also an important solute for increasing stomatal turgor pressure. In conclusion, GC acts more like a sink (receives sugar) than a source (providing sugar) tissue. Their function is closely correlated with the function of MC and regulates CO efficiently.2 Uptake through pores and CO2 Fixed with MC.

“I was very excited when Dr. Lim contacted me to cooperate with this project,” said Dr. Diana Santeria. “We’ve been trying to clarify these basic questions using a molecular genetics approach. Combining their expertise was a winning strategy,” she continued. Dr. Sheyli LIM, the first author of the article and a former PhD. Students in Lim’s group said: “The in-plant fluorescent protein sensor we have developed is a powerful tool for visualizing dynamic changes in the concentration of energy molecules in individual plant cells and organelles, and is of some importance in plant bioenergy. Can solve problems. Publish our findings at Nature Communications We are using this new technology. ”

Rethinking the energy flow of photosynthetic plant cells

For more information:
Shey-Li Lim et al, Arabidopsis guardian chloroplasts import cytosol ATP for starch turnover and stomatal opening. Nature Communications (2022). DOI: 10.1038 / s41467-022-28263-2

Quote: How chloroplasts in guard cells acquire energy (February 10, 2022) February 10, 2022

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How guard cell chloroplasts gain energy

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