INATE AND PHOTO-CONTROLLED MITOTIC RHYTHMS IN ONION ROOT-TIP CELLS

Abstract

A four-peaked diurnal rhythm in mitotic activity of dark-grown onion root-tip cells is initiated upon seed imbibition, damps rapidly and is lost within 5 days. It is abolished by continuous white fluorescent light, by continuous blue, green or red radiation, by low temperatures, high osmotica or anoxia. Photoperiodic light controls the well-known two-peaked persistent rhythm. The nature of the zeitgeber for either the inate or the photoperiodically-controlled rhythms is unknown.