Casparian bands occur in the periderm of XXXX stem and root.

@entity7652 @entity31470 @entity4197 @entity27043 @entity9308
BACKGROUND AND AIMS: Casparian bands are characteristic of the endodermis and exodermis of roots, but also occur infrequently in other plant organs, for example stems and leaves. To date, these structures have not been detected in phellem cells of a periderm. The aim of this study was to determine whether Casparian bands occur in phellem cells using tests that are known to detect Casparian bands in cells that also contain suberin lamellae. Both natural periderm and wound-induced structures were examined in shoots and roots. METHODS: Using @entity27043 as a candidate species, the following tests were conducted: (1) staining with @entity7652 and counterstaining with @entity31470 , (2) mounting sections in concentrated @entity4197 and (3) investigating the permeability of the walls with @entity7652 as an apoplastic, fluorescent tracer. KEY RESULTS: (1) @entity7652 - @entity9308 blue staining revealed a modification in the radial and transverse walls of mature phellem cells in both stems and roots. Three days after wounding through to the cortex of stems, the boundary zone cells (pre-existing, living cells nearest the wound) had developed vividly stained primary walls. By 17 d, staining of mature phellem cells of wound-induced periderm was similar to that of natural periderm. (2) Mature native phellem cells of stems resisted acid digestion. (3) @entity7652 was excluded from the anticlinal (radial and transverse) walls of mature phellem cells in stems and roots, and from the wound-induced boundary zone. CONCLUSIONS: Casparian bands are present in mature phellem cells in both stems and roots of @entity27043 . It is proposed that Casparian bands act to retard water loss and pathogen entry through the primary cell walls of the phellem cells, thus contributing to the main functions of the periderm.
