Abstract
Double-stranded DNA and in a lesser degree ATP reduce the inhibitory action of actinomycin D on auxin-induced elongation growth. The reduction of inhibition by DNA is significant in the initial phase of elongation up to the 4th hour of growth. The effect of ATP is similar but less pronounced. Both substances applied jointly do not completely abolish the inhibitory action of actinomycin D. The foregoing data and the kinetic characteristic of the auxin-induced elongation in the presence of actinomycin D suggest that this antibiotic inhibits growth by blocking synthesis of RNA essential for elongation growth and causes, moreover, certain distinct cellular changes which cannot be explained by the inhibition of DNA-depend RNA synthesis.