Growth‐Factors and Nucleic Acid Synthesis in <i>Helianthus tuberosus</i>

Abstract

Abstract The study of the physiological significance of polyamines in higher plants has induced us to examine both the relationship between these compounds with indol‐3yl‐acetic acid (IAA) and the site of action of polyamines in the cell. Slices of dormant tubers of Helianthus tuberosus were activated with water, 2 × 10 ‐6 M IAA, 10 ‐4 M spermidine and two different concentrations of actinomycin D alone and with spermidine. The RNA synthesis caused by spermidine was similar to that caused by IAA. These data agreed with the hypothesis that the nucleic acid synthesis caused by IAA could be mediated by polyamine synthesis previously observed. Besides 10 ‐4 M spermidine removed the inhibition of 1.5 × 10 ‐6 M actinomycin D on nucleic acid synthesis. As the interaction necessarily occurs between spermidine and actinomycin at the DNA level, it therefore was possible to demonstrate that the primary site of action of spermidine in protein synthesis might occur on DNA also in vivo.