Involvement of Superoxide Radical in Extracellular Ferric Reduction by Iron-Deficient Bean Roots

Toxic effects of Heterosigma akashiwo do not appear to be mediated by hydrogen peroxide

“…Alternatively, in nonsiderophore systems, one method of iron uptake is the reduction of free ferric iron or organically bound ferric iron mediated by ferric chelate reductases (Schmidt 1999). It has been suggested that superoxide may be the electron-rich intermediate that acts in conjunction with these reductases to maintain the high degree of reducing power (Cakmak et al 1987). Recently, it has been shown that H 2 O 2 production by H. akashiwo is inversely proportional to iron availability (Twiner and Trick 2000), suggesting a relationship between iron and ROS.…”

The pH Requirement for in Vivo Activity of the Iron-Deficiency-Induced "Turbo" Ferric Chelate Reductase (A Comparison of the Iron-Deficiency-Induced Iron Reductase Activities of Intact Plants and Isolated Plasma Membrane Fractions in Sugar Beet)

“…In our case, when using plants grown with CaCO,, this ratio decreased from values of 10 at pH 6.0 to less than 3 at pH 6.5. The FC-R activity has been shown to be pH dependent in excised roots of bean (Cakmak et al, 1987) and rape (Toulon et al, 1992). In bean, the ratios of FC-R activity in Fe-deficient and control plants were approximately 20, 17, 12, and 5 at pH 6.0, 6.5, 7.0, and 7.5 (data estimated from figure 2 in Cakmak et al [1987]).…”

“…The FC-R activity has been shown to be pH dependent in excised roots of bean (Cakmak et al, 1987) and rape (Toulon et al, 1992). In bean, the ratios of FC-R activity in Fe-deficient and control plants were approximately 20, 17, 12, and 5 at pH 6.0, 6.5, 7.0, and 7.5 (data estimated from figure 2 in Cakmak et al [1987]). In rape, the decrease in FC-R activity was marked at pH values above 6.0, although no data were reported for control, Fe-sufficient plants.…”

“…The relationships among a11 of these different responses within strategy I, however, are not clear. The increase in the capacity to reduce Fe is thought to be due to the existence of a Fe reductase enzyme in the PM of the deficient plants (Bienfait, 1985(Bienfait, , 1988aCakmak et al, 1987). The existence of not only one, but two, different Fe reductases in the plant root PM was postulated by Bienfait and co-workers in a series of papers (Bienfait et al, 1983Bienfait, 1985Bienfait, , 1988a.…”

The generation of oxygen radicals during host plant responses to infection

“…Aver'yanov [6] has observed a superoxide-generating system in intact pea roots which is enhanced following wounding. H0 2 /0 2~ may also be involved in the reduction of extracellular transition metal ions by some dicotyledon roots under conditions of nutrient deficiency [26,27].…”