SYMBIOTIC AND NON-SYMBIOTIC PLANT HEMOGLOBINS: FUNCTIONS AND EVOLUTION
At present 3 types of hemoglobins are found in plants: symbiotic (Sgb), non-symbiotic (Nsgb) and truncated (Trgb). Symbiotic hemoglobins are synthesizing only during formation of nitrogen-fix- ing symbiosis and work as oxygen reservoirs and transporters. These hemoglobins can also partici- pate in detoxification of reactive nitrogen species. Non-symbiotic and truncated hemoglobins are localizing in tissues of both symbiotic and non-symbiotic organs. Non-symbiotic hemoglo- bins provide plant adaptation to flood hypoxia. It is proposing that evolutional transfer of non- symbiotic hemoglobins to symbiotic ones was ac- companied with changing of Fe coordination from hexa to penta state. It was resulted in decreasing of activation energy of oxygen binding to heme and allowed hemoglobins to bind and transport oxygen what is necessary for support of nitrogenfixation in nodules.