Auxin-Induced Regulation of Protein Synthesis in Tobacco Mesophyll Protoplasts Cultivated In Vitro: II. Time Course and Level of Auxin Control.

When protoplasts, previously cultivated in a medium lacking auxin, are transferred to complete medium, proteins whose synthesis is stimulated by the hormone become detectable after about 30 minutes and reach a constant level 2 to 4 hours after the beginning of hormonal treatment. In contrast, proteins whose level of synthesis is reduced by auxin, are only affected after 6 hours of treatment.Short radioactive labelings in deficient medium followed by chases in complete medium show that auxin does not interfere with posttranslational processes.Analysis of in vitro translation products of protoplast RNA shows that the time courses of auxin effects on protein synthesis and mRNA accumulation are perfectly superimposable. This allows us to exclude the possibility that auxin affects the translation process, but indicates that this hormone acts by regulating the concentration of the auxin-sensitive protein mRNAs.