Phosphorylation of Ribosomal Proteins Induced by Auxins in Maize Embryonic Tissues

The effect of auxin on ribosomal protein phosphorylation of germinating maize (Zea mays) tissues was investigated. Two-dimensional gel electrophoresis and autoradiography of [(32)P] ribosomal protein patterns for natural and synthetic auxin-treated tissues were performed. Both the rate of (32)P incorporation and the electrophoretic patterns were dependent on (32)P 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 K(m) values significantly different for auxin-treated and nontreated tissues. These findings suggest that auxin might exert some kind of translational control by regulating the phosphorylated status of ribosomal proteins.