Newly identified enzymes help plants sense elevated CO2 and could lead to water-wise cropsDecember 14, 2009
Plants take in the carbon dioxide 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. Enzymes that react with CO2 cause cells surrounding the opening of the pores to close down they report in the journal Nature Cell Biology online December 13.
The discovery could help to boost the response in plants that do not take full advantage of elevated levels of the gas, Schroeder says. "A lot of plants have a very weak response to CO2. So even though atmospheric CO2 is much higher than it was before the industrial age and is continuing to increase, there are plants that are not capitalizing on that. They're not narrowing their pores, which would allow them to take in CO2, while losing less water," he said. "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."
Plants lose 95 percent of the water they take in to evaporation through these pores, also called stoma. Modifying crops to be more responsive to CO2 could help farmers meet demand for food as competition for water increases. In California, for example, 79 percent of water diverted from streams and rivers or pumped from the ground is used for agriculture according to the California Department of Water Resources.
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.
Adding extra copies of the genes to the guard cells actually improved water efficiency, the researchers found. "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."
The action of carbonic anhydrases is specific to changes in CO2, the researchers found. Mutant plants still open their pores in response to blue light, a sign that photosynthesis can begin. And their pores also shut when water is scarce, a response mediated by a plant drought-stress hormone.
Photosynthesis continued normally in the mutants as well, suggesting that altering CO2 sensitivity wouldn't stunt growth - good news if the goal is to engineer drought-resistant crops with robust yields.
But saving water and surviving heat involves a tradeoff for plants: Evaporation of water through the pores also cools the plant, just like sweat cools human beings. If future growing conditions are hotter and drier, as they are predicted to be in some parts of the world, then modifications to the CO2 response will need to be carefully calibrated.
University of California - San Diego
Related Enzymes Current Events and Enzymes News Articles
Proteins' passing phases revealed
A new method to identify previously hidden details about the structures of proteins may speed the process of novel drug design, according to scientists at Rice University.
New target identified for preventing bone destruction in diseases such as arthritis and cancer
The skeleton is constantly being remodelled by the breakdown of old bone by cells called osteoclasts and the formation of new bone by cells called osteoblasts.
Scientists discover new survival mechanism for stressed mitochondria
Scientists at The Scripps Research Institute (TSRI) have discovered a natural mechanism that cells use to protect mitochondria, the tiny but essential "power plants" that provide chemical energy for cells throughout the body.
Gene therapy bolsters enzyme activity to combat Alzheimer's disease in mice
St. Jude Children's Research Hospital scientists have identified an enzyme that can halt or possibly even reverse the build-up of toxic protein fragments known as plaques in the brains of mice with Alzheimer's disease.
Detailed image shows how genomes are copied
For the first time, researchers at Umea University have succeeded in showing how the DNA polymerase epsilon enzyme builds new genomes.
Treatment target identified for a public health risk parasite
In the developing world, Cryptosporidium parvum has long been the scourge of freshwater.
MD Anderson researchers identify a rescuer for vital tumor-suppressor
A protector for PTEN, a tumor-thwarting protein often missing in cancer cells, has emerged from research led by scientists at The University of Texas MD Anderson Cancer Center published online at Nature Cell Biology this week.
Scientists stitch up photosynthetic megacomplex
When sunlight strikes a photosynthesizing organism, energy flashes between proteins just beneath its surface until it is trapped as separated electric charges.
Researchers find a missing component in effort to create primitive, synthetic cells
A team of Massachusetts General Hospital (MGH) investigators working to create "protocells" - primitive synthetic cells consisting of a nucleic acid strand encased within a membrane-bound compartment - have accomplished an important step towards their goal.
Broken cellular 'clock' linked to brain damage
A new discovery may help explain the surprisingly strong connections between sleep problems and neurodegenerative conditions such as Alzheimer's disease.
More Enzymes Current Events and Enzymes News Articles