Development of endodermal Casparian bands and xylem in lateral roots of broad bean

摘要

A clearing and fluorochrome staining procedure for broad bean (Vicia fabaL. cv. Windsor) roots with laterals was devised which allowed observation of their tracheary elements and Casparian bandsin situ. The Casparian band of the main root overlying the primordium disappeared early in its development and the margins of the remaining band were displaced outward during subsequent growth of the lateral. The Casparian band matured centripetally in parenchyma across the base of the lateral as far as the endodermis of the lateral and then acropetally into the lateral itself. Casparian bands of the laterals were always connected to those of the main roots. In actively growing roots, the primordium may have emerged as far as 2.7ensp;mm from the main root and still contain no differentiating xylem or Casparian band. Longer laterals contained differentiating xylem 3ensp;mm from the tip and maturing Casparian bands 5ensp;mm from the tip. In nongrowing roots, some primordia not yet emerged from the main root had mature xylem tracheary elements 0.4ensp;mm from the tip and mature Casparian bands 0.25ensp;mm from the tip.Key words: Casparian band, primary xylem, lateral roots, endodermis.