INTERACTION OF LIGHT AND GRAVITROPISM WITH NUTATION OF HYPOCOTYLS OF ARABIDOPSIS-THALIANA SEEDLINGS

Etiolated seedlings of Arabidopsis thaliana nutated under conditions o f physiological darkness while about ten percent of monitored individu als exhibited regular elliptical nutation, circumnutation. Pre-irradia tion with red light prevented occurrence of circumnutation without hav ing an effect on the average rate of the nutational movement. Phototro pic response of seedlings to unilateral blue light appeared to be supe rimposed over nutation. Throughout gravitropism, some seedlings contin ued to exhibit nutation suggesting that these two processes are indepe ndently controlled. Based on these results, we suggest that nutation i n Arabidopsis probably is not controlled by the mechanism predicted by the theory of gravitropic overshoots.