Abstract
All plants examined to date possess non-symbiotic hemoglobin that is genetically and structurally distinct from its symbiotic counterpart (leghemoglobin). Although the ubiquitous distribution of this hemoprotein in the plant kingdom strongly suggests its potential importance, the physiological function remains unknown. To examine the possible participation in inorganic nitrogen/reactive nitrogen metabolism, we studied on an Arabidopsis non-symbiotic hemoglobin, AtGLB1, and found:
(1) AtGLB1 mRNA increased in response to nitrate and nitrite.
(2) Recombinant AtGLB1 (rAtGLB1) exhibited peroxidase activity.
(3) rAtGLB1 was nitrated on its tyrosine residues when nitrite was used as the electron donor in peroxidase reaction, indicating the formation of nitrogen dioxide from nitrite.
These results suggest that AtGLB1 might be involved in nitrite metabolism. Nitrite, a metabolic intermediate in nitrate assimilation, is regarded a reactive nitrogen species whose accumulation is poisonous to plants. Possible roles of AtGLB1 will be discussed in view of defense against nitrite toxicity.
