Circumnutations of Arabidopsis thaliana Seedlings

Abstract The hypocotyls of Arabidopsis thaliana seedlings exhibit circumnutations with different frequency ranges. Using a picture-analysis system, two types of oscillations were distinguished, short period (SPN) and long period nutations (LPN). The period of the SPNs is between 20 and 60 min, decreases with increasing temperature (between 20° and 30°C; Q 10 of 2.0) and increases with age. The SPNs changed frequently between circular and pendular movements. The circumnutation usually occurred clockwise, but the direction could change. For SPNs to occur, a minimum growth rate of 0.05 mm/h was required. The period of the LPNs ranged from 1 to 8 h. Peaks occurred around 95 and 200 min. The movements of the LPNs are mostly counterclockwise. The oscillation could change from circular to elliptic or pendular. In contrast to SPNs, LPNs were found also at low growth rates. Under red light and in the strain Landsberg erecta the circumnutations were especially slow. Short and long period oscillations can occur simultaneously or separately in different plants. In cases of simultaneous occurrence the quotient between the period lengths of the LPN and SPN was not constant. The number of occurrences of these frequencies depended on the strain and on external factors such as temperature and light. In continuous bright white light phases of circumnutations alternated with quiescent periods. This behaviour was circadian and correlated with growth bursts.