Plasma membrane‐bound NADH: Fe³⁺‐EDTA reductase and iron deficiency in tomato (Lycopersicon esculentum). Is there a Turbo reductase?

Abstract

1990. Plasma membrane-bound NADH: Fe'+-EDTA reductase and iron deficiency in tomato {Lycopersicon esculentum). Is there a Turbo reductase? -Physiol. Plant. 79: 339^346.The properties of NADH-dependent Fe^*-EDTA reductase in plasma membranes (PM) from roots of iron-deficient and -sufficient tomato plants \Lycopersicon esculentum L. (Mill.) cv. Abunda] were examined. Iron deficiency resulted in a 3-fold increase of in vivo root iroB-chelate reductase activity with a K^ (Fe'+-EDTA) of 230 M.ln purified root PM, average specific activities of ferric chelate reductase of 410 and 254 nmol Fe (mg protein)"' min'' were obtained for iron-deficient and -sufficient plants, respectively. In both cases, the PM-bound activity showed a pH optimum at pH 6.8. Activity depended on NADH and not on NADPH and on the presence of detergent. The activity was inhibited 40-50% by superoxide dismutase (EC 1.15.1.1) and ca 30% by oxygen. Kinetic analysis of the membrane-boand enzyme revealed a K^ (Fe'^-EDIA) of ca 200 \iM for both iron-stressed and -sufficient plants. For NADH, Kjn values around 230 \iM were obtained. The ferric chelate reductase could be solubilised from salt-washed PM with Triton X-100 at a protein:detergent ratio of 1:2.8 (w/w). The Triton-soluble fraction revealed one enzyme-stained band in native polyacrylamide electrophoresis. Although the membranes showed no nitrate reductase (NR; EC 1,6.6.1) activity, anti-spinach NR immunoglobulin G (IgG) recognized a 54 kDa band both in the PM and the Triton-soluble fraction, but not in the enzymatically active material obtained from the native gel. No evidence could be found for the synthesis of a new, biochemically distinct PM-bound ferric chelate reductase under iron deficiency, which might be identified as the so-called Turbo reductase. It is concluded that iron deficiency in tomato induces increased expression of a ferric chelate reductase in root PM, which is already present in iron-sufficient plants and probably also in plants,, which do not contain the Turbo reductase, like the grasses. The iron reductase is not identical with the recently reported PM-associated nitrate reductase.

Cu2+ Reduction by Tomato Root Plasma Membrane Vesicles

“…The specific activity of the reduction of Cu was lower than the Fe-chelate reductase activity, measured with Fe citrate. PM vesicles isolated from Fe-deficient plants exhibited higher levels of Fe-citrate reductase activity than did vesicles from Fe-sufficient plants, as has been observed previously (Buckhout et al, 1989;Bruggemann et al, 1990;Chosack et al, 1991;Holden et al, 1991;Valenti et al, 1991). There was an increase in the rate of Cu reduction by PM vesicles from Fe-deficient plants over that seen in Fe-sufficient plants.…”

“…Fe-chelate reductase activity has been been measured and characterized in PM vesicles isolated from a number of plant species in recent years (Buckhout et al, 1989;Bruggemann et al, 1990;Schmidt et al, 1990;Chosack et al, 1991;Holden et al, 1991;Schmidt and Janiesch, 1991;Valenti et al, 1991). PM vesicles provide a logical system for investigating the identity of the enzyme in the PM responsible for Cu reduction and the nature of the activity.…”

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)

“…Vol. 11 O, 1996 Briiggemann andMoog, 1989) and subsequently in strategy I plants such as tomato (Buckhout et al, 1989;Briiggemann et al, 1990;Holden et al, 1991Holden et al, , 1992Valenti et al, 1991), bean (Schmidt and Janiesch, 1991b), Plantago (Schmidt et al, 1990), Geum urbanum (Schmidt and Janiesch, 1991a), Vigna unguiculata (Briiggemann et al, 1993), and Arabidopsis tkaliana (Moog et al, 1995). However, the PM from Fe-deficient plants usually exhibits FC-R activities biochemically similar to those of PM from control plants.…”

Redox enzymes in the plant plasma membrane and their possible roles

“…However, polyclonal antibodies raised against the soluble NR from spinach leaves did not cross-react with purified PM-associated NADH-Fe 3+ -EDTA oxidoreductase from tomato roots indicating that the two enzymes are not closely related (Brüggemann et al 1990). Similar experiments have not been done with the 205 kDa NADH-Fe 3+ -EDTA oxidoreductase from barley roots.…”