The effect of auxin on ribosomal protein phosphorylation of germinating maize (Zea mays) tissues was investigated. Twodimensional gel electrophoresis and autoradiography of [32P] ribosomal protein pattems for natural and synthetic auxin-treated tissues were performed. Both the rate of 32P incorporation and the electrophoretic pattems were dependent on 32P pulse length, suggesting that active protein phosphorylation-dephosphorylation occurred in small and large subunit proteins, in control as well as in auxin-treated tissues. The effect of ribosomal protein phosphorylation on in vitro translation was tested. Measurements of poly(U) translation rates as a function of ribosome concentration provided apparent Km values significantly different for auxintreated and nontreated tissues. These findings suggest that auxin might exert some kind of translational control by regulating the phosphorylated status of ribosomal proteins.

Pérez, L., Aguilar, R. and Sánchez‐de‐Jiménez, E. 1987. Effect of an exogenous auxin on maize tissues. Alteration of protein synthesis and phosphorylation. ‐ Physiol. Plantarum 69: 517–522.A synthetic auxin 2‐(2‐methyl‐4‐chloro)phenoxypropionic acid (MCPP), analogue of 2,4‐D, alters maize (Zea mays L. H‐30) germination while inducing callus formation. The effect of this auxin on protein synthesis and phosphorylation of the embryonic tissues was explored. Total cytoplasmic proteins were analysed for 14C or 32P incorporation into trichloroacetic acid precipitable material. MCPP significantly stimulated protein synthesis as well as protein phosphorylation. The protein synthesis pattern was highly altered in the presence of MCPP as analysed by two‐dimensional gel electrophoresis. Analyses by Sephadex G‐100 chromatography and by two‐dimensional gel electrophoresis of phosphorylated proteins indicate that the effect of MCPP on protein phosphorylation was only quantitative.

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