Hemoglobin is a protein-iron compound found within the red blood cells of most vertebrates and is responsible for the cell's red pigment. These red blood cells carries oxygen from the lungs to the rest of the tissue cells throughout the rest of the body. Just as hemoglobin transports oxygen in humans, they have also been found transporting oxygen within plants. In plants, there are two types of hemoglobin that can be found; symbiotic and non symbiotic. Oxygen is used in the mitochondria of plant cells. Symbiotic hemoglobin known as leghemoglobin, is foun"d in the root nodules of leguminous plants. Leghemoglobin functions as an oxygen carrying red pigment caused by symbiotic nitrogen fixation. The nitrogen fixing bacteria Rhizobia is what affects the roots of the plants causing leghemoglobin to be produced as a part of the symbiotic interaction between the bacterium and the plants. Leghemoglobin supplies the respiring bacterium cells with oxygen just as hemoglobin supplies vertebrate cells with oxygen. The three-dimensional structures of the two oxygen carrying pigments are very similar suggesting they may have shared a common aqncestor. Non symbiotic is the second type of plant hemoglobin that also shows a different structure from hemoglobin and leghemoglobin but, they all are similar. Again suggesting a common ancestor or even a mutation in the symbiotic leghemoglobin resultimg in non symbiotic hemoglobin. Non symbiotic plant hemoglobin are found ubiquitous in plants including in the roots, unlike leghemoglobin that are found only in bacterium affected plant roots. They are found in low concentrations in plant tissue throughout the plant resulting from growth within an environment with limited O2 concentration . These non symbiotic hemoglobin proteins have the higest affinity for oxygen out of vertebrate hemoglobin and leghemoglobin. They are said to function as oxygen level sensors, oxygen transporters, and many other...
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