Auxin-induced cell wall loosening in the presence of actinomycin D.

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Abstract
An Instron stress-strain analyzer was used to determine the effects of various treatments on the extensibility (WEx) of Avena coleoptile cell walls. Auxin caused an increase in WEx even when RNA synthesis was inhibited by more than 90% with actinomycin D. Furthermore, the effect of auxin on WEx persisted even after auxin-induced elongation had been completely blocked by the actinomycin. It is apparent that RNA synthesis is not necessary for auxin-induced wall loosening, but is necessary for some other factor required for elongation. Cyanide completely prevented an effect of auxin on WEx. Aerobic metabolism was apparently necessary for the induction of wall loosening by auxin. Removal of auxin from sections resulted in a parallel decrease in the growth rate and in WEx. It would appear that wall loosening is used up in elongation.