Hemoglobin-like protein that exhibits an unusual concentration-independent binding of O(2) and CO. May promote shoot organogenesis from root explants in vitro (PubMed:11526234, PubMed:21741261). Inhibits RGLG3 and RGLG4 ubiquitination activity (PubMed:27497447). Binds 1 heme group per subunit. The absorbance spectrum of deoxy-GLB3 is unique as the protein forms a transient six-coordinate structure with absorption peaks at 538 and 565 nm after reduction and deoxygenation, which slowly converts to a five-coordinate structure with an absorption peak at 548 nm. Homodimer when ferric (Probable). Interacts with RGLG3 and RGLG4 (PubMed:27497447). Expressed ubiquitously, with higher levels in root tissue than in shoot tissue. Slight reduction of the number of shoots produced by root explants in vitro; root explants are first cultured on an initial auxin-rich callus induction medium (CIM) followed by a transfer onto a cytokinin-containing shoot induction medium (SIM). Belongs to the truncated hemoglobin family. Group II subfamily.