EFFECT OF IN-VIVO IRON SUPPLEMENTATION ON OXYGEN RADICAL PRODUCTION BY SOYBEAN ROOTS

Both total iron content and the in vitro rate of iron reduction were h igher in roots grown in the presence of exogenously added iron (up to 500 mu M) than in roots grown in absence of supplemented iron. In vivo generation of reactive O-2 species by intact roots was assessed emplo ying 2',7'-dichlorofluorescein diacetate oxidation to a fluorescent pr oduct. Roots developed in the presence of 500 mu M Fe-EDTA, showed sig nificantly increased fluorescence (64%), as compared to roots develope d in absence of added iron, suggesting that iron supplementation led t o oxidative stress in vivo. At the subcellular level, iron content and Fe-EDTA reduction rate were significantly increased in microsomes iso lated from roots developed in the presence of exogenously added iron, as compared to microsomes from roots grown in the absence of iron. Mic rosomes from Fe supplemented plants exhibited a 51% increase in 2',7'- dichlorofluorescein diacetate oxidation rate, a 55% increase in supero xide anion generation, and a four-fold increase in hydroxyl radical pr oduction as compared to controls. Iron supplementation did not affect the activity of antioxidant enzymes or the content of total thiols, ho wever alpha-tocopherol content was significantly decreased in the homo genates and the microsomes isolated from roots supplemented with iron, as compared with values in roots developed in absence of iron. These data suggest that in vivo iron supplementation increased oxygen radica l generation.