CLUSTER ROOT DEVELOPMENT IN GREVILLEA-ROBUSTA (PROTEACEAE) - II - THEDEVELOPMENT OF THE ENDODERMIS IN A DETERMINATE ROOT AND IN AN INDETERMINATE, LATERAL ROOT

Light, fluorescence and electron microscopy were employed to follow th e development of the endodermis in cluster roots and lateral roots of Grevillea robusta A. Cunn. ex R. Br. Endodermal cells had three differ ent origins: rootlet endodermis arose from the rootlet meristem; endod ermis covering the primordium shortly after initiation came from divis ion of parental endodermis; cells at the junction between parent and r ootlet endodermis developed from re-differentiated rootlet cortical ce lls. In the cluster root, the Casparian band formed in three ways, and was not initially present opposite the two sets of single xylem eleme nts in the rootlet stele. A new clearing technique was developed that allowed visualization of xylem, suberized endodermis, Casparian band f ormation and phenolic compounds. In lateral roots, endodermal differen tiation was asynchronous, but was related to position relative to prot oxylem poles. However, the observed delay began before these poles had differentiated. At the tip of mature rootlets, which are determinate, the endodermis terminates in a 'dome' of cells, with the initial cell differentiating as an endodermal cell. Results are discussed in terms of determinate development in roots and the spatial and temporal cont exts within which this development takes place.