Modification of the gravitropic response of seedling roots of rapeseed {Brassica napus) transformed by Agrobacterium rhizogenes A4 V. Legue, F. Vilaine, M, Tepfer and G, Perbal Legue. V,. Vilaine, E. Tepler. M. and Perbal. G. 1994. Modification ofthe gravitropic response of seedling roots of rapeseed \Bra.ssica napii.\i transformed by Agrobacieiium rhi:ngem's A4,-Physiol, Plant, 91: 559-566. We have e.xamlued the growth and gra\ itropic response of seedling roots of rapeseed {Brassica napus. CrGC5-l) transformed by AgrobacWiiiini rhizogenes .\4. in order to evaluate if this could constitute a new model system for the study of gravitropism. The transformed clone chosen for study had integrated full-length TL-and TR-D.NA from pRi (the root inducing piasmid). and thus included all of the agrobacteriai genes potentially involved in the modified phenotype of transformed plants. In the vertical position, the gnnvth rate of transformed roots was higher than controls. During 24 h of continuous stimulation, the optimal angle for gravitropic bending in normal roots was 135° twith respect to the gravity a.sis). with decreasing response at 90° and 45^, Eor transformed roots, slight curvature developed at 45"' and at 90°. and stronger curvature was observed at 135. though transformed root tips never reached the vertical position. The minimum stimulation time necessary to elicit a response (presentation time) was also determined: it was significantly shorter in normal roots t80 si than in transformed ones * 120 s). The results show that pRi transformed roots are less sensitive to gravity than normal roots.