Activated oxygen and antioxidant defences in iron-deficient pea plants

22 Pags. The definitive version, with Figs. and Tabls., is available at: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-3040
Iron (Fe) deficiency in pea leaves caused a large decrease (44–62&) in chlorophyll a, chlorophyll b and carotenoids, and smaller decreases in soluble protein (18&) and net photosynthesis (28&). Catalase, non-specific peroxidase and ascorbate peroxidase activities declined by 51& in young Fe-deficient leaves, whereas monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase activities remained unaffected. Ascorbate peroxidase activity was highly correlated (r2= 0. 99, P < 0. 001) with the Fe content of leaves, which allows its use as an indicator of the Fe nutritional status of the plant. Fe deficiency resulted in an increase of CuZn-superoxide dismutase but not of Mn-superoxide dismutase. The content of ascorbate decreased by only 24& and those of reduced and oxidized glutathione and vitamin E did not vary. The low-molecular-mass fraction of Fe-sufficient leaves contained 30–65 μg (g dry weight)−1 Mn. This concentration was 15–60 times greater than that of Fe and Cu in the same fraction, and was further enhanced (1. 5- to 2. 5-fold) by Fe deficiency without causing Mn toxicity. The concentration of catalytic Fe, that is, of Fe active for free radical generation, was virtually zero and that of catalytic Cu did not change with severe Fe deficiency. Because catalytic metals mediate lipid and protein oxidation in vivo, the above findings would explain why oxidatively damaged lipids and proteins do not accumulate in Fe-deficient leaves.
I.I.O. and J.F.M. were the recipients of predoctoral fellowships from the Comunidades Autónomas del País Vasco and Aragón, respectively, and Y. Gogorcena was the recipient of a postdoctoral contract from the Mininsterio de Educación y Ciencia. This work was supported by grant PB92-0058 from the Dirección General de Investigación Científica y Técnica to M.B. and grant 93-0318 from the U.S. Department of Agriculture to R.V.K.