Sulfhydryl Localization and Tetrazolium Reduction. 1. Reversible Inhibition of its Reduction by N-Ethyl Maleimide

The sulfhydryl inhibitor N-ethyl maleimide completely inhibited the reduction of 2,3,5-triphenyltetrazolium chloride in meristematic and embryonic vascular tissues of Coleus sp. stems, Ricinus communis root tips, ungerminated Tea mays embryos, and epicotyls and coleoptiles of germinated Tea mays embryos, in a concentration of 200 mg/lit. Inhibition was reversed by the addition of cysteine or reduced glutathione (200 mg/lit) to the inhibitor medium. N-ethyl maleimide was effective also in blocking the nitro-prusside and 1-(4-chIoromercuriphenylazo)-naphthol-2 sulfhydryl staining reactions, but other substituted maleimides were ineffective in inhibiting the tetrazolium reaction in these tissues. Experiments were conducted to determine the histological pattern of sulfhydryl groups as indicated by a modification of the Bennett 1-(4-chloro-mercuriphenylazo)-naphthol-2 test and a modification of the Rap-kine nitroprusside test in certain plant tissues. A positive correlation was observed between tissues reducing the tetrazolium indicator and tissues exhibiting sulfhydryl localization as indicated by the nitroprusside reagent (trichloroacetic acid pretreated) and 1—(4— chloromercuriphenylazo)—naphthol—2.