VISUALIZATION OF THE RADICLE WITHIN THE AXIS OF DEVELOPING AND GERMINATING BRASSICA-NAPUS L EMBRYOS

A method is presented for visualizing the exact radicle territory with in the developing embryo axes of Brassica napus L. (rape). The reactiv e dye, Procion Blue MX-R, when used for embryo axes in tote, showed a definite staining pattern. The basal boundary of the stained region (l evel L2) did not coincide with the basal radicle cap boundary (level L I), and, on average, 16 rhizodermal cells were observed between these boundaries in maturing and mature embryos. In all stages of developing embryos, from the torpedo stage to maturity, the embryo hypocotyl was not stained, and the stained region revealed the proper radicle terri tory. This conclusion was based on the following observations: (1) the staining patterns in the developing, developed and germinating embryo s were similar; (2) direct observations of the basal part of the stain ed L1-L2 region demonstrated that its cells began fast elongation 24 h r after seed imbibition and began root hair formation just before the completion of elongation; (3) root hairs did not emerge after decapita tion of the entire stained region which was done 24 hr after the begin ning of seed imbibition; (4) at this time (24 hr post-initiation of im bibition) decapitation at level L1 stopped radicle growth for 24 hr, a nd hairs emerged in the apical portion of the axes; and (5) cross-sect ions of the L1-L2 zone of seedlings revealed a vascular system typical of root. Stainability is a complex reaction which combines interactio n of the dye with the surface of radicle cells and its penetration int o outer tissue cells of the radicle. Differential stainability of the hypocotyl and the radicle within the axes of developing and germinatin g B. napus L. embryos might be partially related to the presence of cu ticle on the hypocotyl surface and its absence on the radicle surface.