Mitotic arrest by Melatonin

We are testing the hypothesis that migration of the newly formed mouth (i.e., oral membranellar band) in stentor is homologous to mitotic chromosomal movement and that both types of movement within single cells depend directly on microtubule elongation. The following compounds synchronously delay the migration of the oral membranellar band as an exponential function of concentration: Colcemid, podophyllotoxin, β-peltatin and vinblastine. Delay for these compounds can be described by the equation, y = kxn, where y is delay in hours and x is concentration of mitotic spindle inhibitor in moles/l. We discovered that the animal pineal gland hormone, melatonin (5-methoxy n-acetyl tryptamine), also specifically and reproducibly delays oral band regeneration according to an equation of this form. Thus we predicted that melatonin would arrest mitosis. We report here a colchicine-type disruption of the mitotic apparatus in onion root tips by melatonin. Two closely related tryptamine derivatives, n-acetyl serotonin and serotonin were inactive in both the stentor and onion assays: they neither delayed band migration in stentor as an exponential function nor induced mitotic arrest in onion