Differences in Root Microscopic Structure of Root Mutants lrn1, prl1 and Wild Type in Oilseed Rape (Brassica napus L.)

Both lrn1 and prl1, two Brassica napus root mutants insensitive to exogenous cytokinin, show phosphorus efficiency. Compared with‘Ningyou 7’(WT) plants, lrn1 produces more lateral roots and prl1 has longer primary roots under 0.2 μmol/L cytokinins (6-BA) treatment by hydroponics. In this study, differences in root hair, differentiation of epidermal cells and anatomical structure of the root tip of all three genotypes under ddH₂O and 0.2 μmol/L 6-BA were studied with stereomicroscopy, non-sliced squash method and paraffin sectioning. Results showed that the root hair number at the zone of maturation in lrn1, prl1 and WT at ddH₂O was significantly less than that under 0.2 μmol/L 6-BA treatment. Under 0.2 μmol/L 6-BA treatment, the root hair length and density of WT was the longest and highest, while that of prl1 was the shortest and lowest, and that of lrn1 was between WT and prl1 3 days after germination (DAG3). The zone of cell division and cell elongation of lrn1, prl1 and WT were shortened under 0.2 μmol/L 6-BA DAG6. The meristem areas of lrn1 and prl1 were greater than that of WT, and there were no differences between these two mutants. Moreover, cell structure of the root cap of lrn1 and prl1 were normal, whereas, that of WT was abnormal. Periblem cell arrangements of lrn1 were closer than that of WT and prl1. Under 0.2 μmol/L 6-BA DAG9, lrn1 had four lateral roots, whereas prl1 and WT had no lateral roots. Longer primary root length of prl1 was closely related to its larger meristem area; and more lateral roots in lrn1 under 0.2 μmol/L 6-BA treatment were due to higher cell density in the plerome in the zone of cell division.