Actinomycin D and the hormonal induction of amylase synthesis in barley aleurone layers.

The induction of amylase synthesis in barley aleurone layers by gibberellic acid is most sensitive to Actinomycin D (AM) over a short interval late in the lag phase. The duration of the lag phase may be extended as much as 3 fold by lower temperatures over the range 30° to 15° C. At each temperature the AM sensitive period remains close to the end of the lag phase, the period we have previously determined as the stage less sensitive to temperature.Lack of sensitivity to the inhibitor at other periods is not due to failure to penetrate, or to degradation. AM has no effect on tissue respiration, leucine, uridine or uracil uptake, leucine incorporation, or leucine pool size. At all stages it inhibits uracil and uridine incorporation into RNA. Thus AM probably acts by inhibiting RNA synthesis.