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Contact: Diana Lutz
Washington University in St. Louis

Why Are Nodules Red?

Caption: An iron-containing protein not unlike the hemoglobin in our red blood cells colors root nodules. Called leghemoglobin (leg- for "legume") it ferries oxygen to the respiring bacteria, just as hemoglobin ferries oxygen to our respiring cells. But leghemoglobin holds oxygen much more tightly than hemoglobin and dispenses it more stingily because oxygen can poison the bacterial enzyme that fixes nitrogen.

Credit: Hari Krisnan

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