Development of the primary root and mobilisation of reserves in etiolated seedlings ofBrassica napus grown on a slowly rotating clinostat

The effect of the slow rotating clinostat (1 rpm) on the growth of the primary root was studied on Brassica napus seedlings. After 5 d in darkness, the primary root was longer and thinner in seedlings grown on the clinostat than in seedlings grown in the vertical position. However, the breakdown of lipid reserves, sucrose level and transport of 14C-labeled sucrose from the cotyledons to the primary root, were not altered by growth on the clinostat. Moreover, the activity of isocitrate lyase, one of the two enzymes necessary for the conversion of lipids into glucids also was also not modified in the cotyledons of clinorotated seedlings. Thus, there was clear evidence that clinorotation had a direct effect on the growth of the primary root that was independent of the mobilisation of lipid reserves in the cotyledons. As a sink, the primary root had the same strength on the clinostat as in the vertical position, but the reserves were used in a different way. The increase in root elongation on the clinostat could be due to the slight, but continuous, omnilateral gravitropic stimulation due to the rotation of the seedlings about a horizontal axis.