Newly identified enzymes may help plants sense elevated CO2

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Washington, December 14 (ANI): Biologists have identified plant enzymes that may help plants sense elevated carbon dioxide (CO2) to use water more efficiently, which could help to engineer crops that take advantage of rising greenhouse gases.

Plants take in the CO2 they need for photosynthesis through microscopic breathing pores in the surface of leaves.

But for each molecule of the gas gained, they lose hundreds of water molecules through these same openings.

The pores can tighten to save water when CO2 is abundant, but scientists didn't know how that worked until now.

A team led by Julian Schroeder, professor of biology at the University of California, San Diego, has identified the protein sensors that control the response.

It was found that enzymes that react with CO2 cause cells surrounding the opening of the pores to close down.

"The discovery could help to boost the response in plants that do not take full advantage of elevated levels of the gas," said Schroeder.

"It could be that with these enzymes, you can improve how efficiently plants use water, while taking in CO2 for photosynthesis. Our data in the lab suggest that the CO2 response can be cranked up," he added.

Schroeder's team identified a pair of proteins that are required for the CO2 response in Arabidopsis, a plant commonly used for genetic analysis.

The proteins, enzymes called carbonic anhydrases, split CO2 into bicarbonate and protons.

Plants with disabled genes for the enzymes fail to respond to increased CO2 concentrations in the air, losing out on the opportunity to conserve water.

Several types of cells in plant leaves contain carbonic anhydrases, including those responsible for photosynthesis, but Schroeder's team showed that the enzymes work directly within a pair of cells, called guard cells, that control the opening of each breathing pore.

By adding normal carbonic anhydrase genes designed to work only in guard cells, they were able to restore the CO2-triggered pore-tightening response in mutant plants.

The researchers found that adding extra copies of the genes to the guard cells actually improved water efficiency.

"The guard cells respond to CO2 more vigorously," said Honghong Hu, a post doctoral researcher in Schroeder's lab and co-first author of the report.

"For every molecule of CO2 they take in, they lose 44 percent less water," he added. (ANI)

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