Independence of Effects of Auxin on Cell Wall Methylation & Elongation

Abstract

Ethionine has been usedto separate the effects of auxin on cell wall methylation and elongation in the Avena coleoptile. The auxin-induced increase in the rate of transfer of methyl groups to both the cold-water-soluble and hot-water-soluble pectic fractions of the wall is completely inhibited by 0.05 [image] DL-ethionine. This inhibition occurs whether the methyl donor is methionine or formaldehyde and whether the methyl donor is added prior to or at the same time as the ethionine. Under the same conditions, 0.05M ethionine causes some inhibition of elongation but does not eliminate the effect of auxin on elongation. Thus auxin-induced elongation can occur under conditions where auxin-induced methylation of pectic substances is completely suppressed. The effects of auxin on cell wall methylation and elongation must be independent. The transfer of methyl groups from formaldehyde to pectins is enhanced by auxin. Ethionine inhibits this transfer. Transfer of ethyl groups from ethionine to the cell wall does not appear to occur in the Avena coleoptile. In the absence of added sugars, auxin does not cause any measurable increase in amount of any of the pectic fractions. Methylation in the Avena leaf is insensitive to auxin.