Iron deficiency differently affects peroxidase isoforms in sunflower

The response of both specific (ascorbate peroxidase, APX) and unspecific (P OD) peroxidases and H2O2 content of sunflower plants (Helianthus annuus L. cv. Her) grown hydroponically with (C) or without (-Fe) iron in the nutrien t solution were analysed to verify whether iron deficiency led to cell oxid ative status. In -Fe leaves a significant increase of H2O2 content was dete cted, a result confirmed by electron microscopy analysis. As regards extrac ellular peroxidases, while APX activity significantly decreased, no change was observed in either soluble guaiacol or syringaldazine-dependent POD act ivity following iron starvation. Moreover, guaiacol-dependent POD activity was found to decrease in both ionically and covalently-cell-wall bound frac tions, while syringaldazine-POD activity decreased only in the covalently-b ound fraction. At the intracellular level both guaiacol-POD and APX activit ies underwent a significant decrease. The overall reduction of peroxidase a ctivity was confirmed by the electrophoretic separation of POD isoforms and , at the extracellular level, by cytochemical localization of peroxidases b y diaminobenzidine staining. The electrophoretic separation, besides quanti tative differences, also revealed quantitative changes, particularly eviden t for ionically and covalently-bound fractions. Therefore, in sunflower pla nts, iron deficiency seems to affect the different peroxidase isoenzymes to different extents and to induce a secondary oxidative stress, as indicated by the increased levels of H2O2 However, owing to the almost completely la ck of catalytic iron capable of triggering the Fenton reaction, iron-defici ent sunflower plants are probably still sufficiently protected against oxid ative stress.