The ultrastructure of Cynodon salt glands: the apoplast

The salt glands of Bermuda grass were found to be similar to those of many dicotyledonous plants with respect to the relatively large quantities of chloride that accumulate in the subcuticular collecting chamber of secreting glands. The salt glands of grasses lack the suberized or cuticularized zone that is present in the walls of the glands of dicotyledonous plants that has been hypothesized to prevent the apoplastic backflow of accumulated salts from the collecting chamber to the leaf mesophyll. An ionic lanthanum solution was used to determine whether or not the apoplastic pathway is blocked between the collecting chamber and the leaf mesophyll. The results of the lanthanum tracer study revealed that this pathway is significantly restricted. It was determined that the restriction of the apoplastic pathway was due to the highly lignified condition of the lateral cell walls in the outer portion of the basal gland cell. The lanthanum tracer study also revealed that an apoplastic continuum exists between the leaf mesophyll and a system of membranous extracellular channels that occur in the basal cell. Based on this finding, it was suggested that the extracellular channels may function in the absorption of solutes from the apoplast.