PUB - Publikationen an der Universität Bielefeld

Symbiotic hemoglobins provide O2 to N2 -fixing bacteria within legume nodules, but the functions of nonsymbiotic hemoglobins or phytoglobins (Glbs) are much less defined. Immunolabeling combined with confocal microscopy of the Glbs tagged at the C-terminus with green fluorescent protein was used to determine their subcellular localizations in Arabidopsis and Lotus japonicus. Recombinant proteins were used to examine NO scavenging in vitro and transgenic plants to show S-nitrosylation and other in vivo interactions with NO and ABA responses. We found that Glbs occur in the nuclei, chloroplasts, and amyloplasts of both model plants, and also in the cytoplasm of Arabidopsis cells. The proteins show similar NO dioxygenase activities in vitro, are nitrosylated in Cys residues in vivo, and scavenge NO in the stomatal cells. The Cys/Ser mutation does not affect NO dioxygenase activity, and S-nitrosylation does not significantly consume NO. We demonstrate an interaction between Glbs and ABA on several grounds: Glb1 and Glb2 scavenge NO produced in stomatal guard cells following ABA supply; plants overexpressing Glb1 show higher constitutive expression of the ABA responsive genes Responsive to ABA (RAB18), Responsive to Dehydration (RD29A), and Highly ABA-Induced 2 (HAI2), and are more tolerant to dehydration; and ABA strongly up-regulates class 1 Glbs. We conclude that Glbs modulate NO and interact with ABA in crucial physiological processes such as the plant's response to dessication. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.