INDUCTION OF FERRITIN SYNTHESIS IN MAIZE LEAVES BY AN IRON-MEDIATED OXIDATIVE STRESS

Oxygen is essential for aerobic life, although reactive oxygen interme diates can be highly toxic to cells. Superoxide radicals and hydrogen peroxide become particularly harmful in vivo due to their reactivity w ith transition metals like iron, producing hydroxyl radicals, which ar e involved in DNA mutagenesis and lipid peroxidation. Con trot of the intracellular concentration of transition metals can prevent hydroxyl radical formation, protecting cells against oxidative damage. The iron storage protein ferritin plays an important role in these processes, and it has been shown that its synthesis is inducible by iron-overload in plants. In this paper, the induction of ferritin synthesis in resp onse to iron-overload is investigated using derooted maize plantlets. In this system, a rapid increase of iron concentration in the leaves i s observed, leading to ferritin mRNA and subunit accumulation. Using t he vp2 maize mutant, it is demonstrated that abscisic acid is not invo lved in this response, in contrast to previous results obtained using plants induced under hydroponic culture. In de-rooted plantlets, ferri tin transcript accumulation is inhibited when plants are co-treated by iron and antioxidant reagents like N-acetyl cysteine or reduced gluta thione. Furthermore, hydrogen peroxide treatment induced a dose-depend ent ferritin mRNA accumulation at a low concentration of iron. It can be concluded from these results that reactive oxygen intermediates are involved in the pathway leading to ferritin synthesis in response to iron in de-rooted maize plantlets. Ferritin emerges, therefore, as an important component of the oxidative stress response in plants.