Ferric chelate reduction by sunflower (Helianthus annuusL.) leaves: influence of light, oxygen, iron-deficiency and leaf age

Abstract

The presence of ferric chelate reducing activity in sunflower [Helianthus annuus L.) leaves has been studied by submerging leaf discs in a solution with Fe(III)-ethylenediaminetetra-acetate (FeEDTA), batho-phenanthroline disulphonate (BPDS) and vacuum infiltration. The effect of different factors on the Fe(III) reduction rate was studied. Ferric reduction rate was about 10-fold higher in the light than in darkness. The light effect was greatly inhibited by 3-(3,4-dichloro-phenyl)-1,1-dimethylurea (DCMU), a photosystem II inhibitor. Several inhibitors of redox systems [cis-platinum (II) diamine dichloride (cis-platin), p-nitro-phenylacetate (p-NPA) and p-hydroxymercuribenzoic acid (pHMB)] decreased the FeEDTA reduction rate. The greatest inhibition was produced by the - SH group reagent pHMB (17% of control, in light). The FeEDTA reduction rate was much higher in the absence of O₂ than with air or 100% O₂. Superoxide dismutase (SOD) decreased FeEDTA reduction with air in the light. Young leaves reduced Fe(III)-chelate at a higher rate than did older leaves. In iron-deficient plants, leaves did not exhibit enhanced ferric chelate-reducing activity as was observed in roots. It is suggested that at least two different redox systems or two states of the same redox system work in the light and in darkness.