Abstract
Within the last 3-4 years, evidence has accumulated to indicate that hemoglobin proteins exist widely in the plant community. This review presents some of the evidence to support this view and describes some of the properties of a barley hemoglobin. Barley hemoglobin has a strong avidity for oxygen, having an oxygen dissociation constant for oxyhemoglobin of 3 nmol L-1. It is induced under low oxygen tensions, with the induction regulated by ATP, or some consequence of ATP action. Experiments with transformed maize cells indicate that hemoglobin acts to improve the energy status of plant cells under low oxygen stress. It is postulated that hemoglobin acts as an oxygenase in plants. The review is a consequence of a CSPP Gold Medal Presentation at the Plant Biology 1997 Meeting in Vancouver, B.C.Key words: nonsymbiotic hemoglobins, hypoxia, barley, flooding tolerance.