Growth inhibition of crown‐gall tissues in relation to the structure and activity of DNA

Abstract

The growth of crown‐gall cells cultured in vitro (Nicotiana tabacum L. cv. White Burley and Parthenocissus tricuspidata cv. Veitchii) is inhibited by alstonine (BG‐8), a plant alkaloid, the anti‐cancer effect of which has previously been demonstrated on animals and plants. The growth of normal cells is only slightly affected. The inhibitory effect of BG‐8 on crown‐gall cells is antagonized by indole‐3‐acetic acid (IAA) added to the culture medium. Kinetin associated with IAA does not prevent this inhibitory effect. BG‐8 present in the culture medium containing the two types of hormones seems to modify the later hormonal requirement of Parthenocissus crown‐gall tissues.BG‐8 exhibits high binding affinity for crown‐gall DNA and, therefore, strongly inhibits its in vitro synthesis. The alkaloid has practically no effect on DNA from healthy cells. The inhibition by BG‐8 is dependent on the level of DNA strand separation and on the origin and nature of the tissues (crown‐gall DNA is more destabilized than healthy DNA; DNA from habituated tissues is intermediate). IAA and kinetin have opposite effects on the in vitro strand separation of the DNAs from crown‐gall cells and, consequently, antagonistic effects on DNA replication (IAA stimulates and kinetin inhibits). It is possible to establish a close relationship between in situ development of crown‐gall tissues of the two species studied (in the presence or absence of BG‐8 or cell‐growth factors), in vitro DNA synthesis and DNA strand separation.