OXIDATIVE STRESS IN NITROGEN-FIXING LEGUME NODULES - SOME BIOCHEMICALAND MOLECULAR-BIOLOGY ASPECTS

Leghemoglobin, the oxygen-carrying hemoprotein present in great amount s in legume nodules, can react with hydrogen peroxide to form phenoxyl radicals. These radicals are quenched by at least two processes : the first one involves an intramolecular heme-protein cross-link and the second route results in the formation of intermolecular cross-links an d hence dimeric forms of the protein. They can also interact with peri bacteroid membrane fractions, leading to the generation of additional lipid-derived radicals. This transfer of damage may be of great biolog ical significance during the nodule senescence process. Glutathione, w hich is present at high concentration in nodules, most probably exerts a very important protective role, as it can react with these radicals . Thus, glutathione synthesis is studied in Medicago truncatula : part ial cDNAs corresponding to the two enzymes involved in this synthesis are cloned and show high homology with their Arabidopsis counterparts.