Apoplastic tracer studies in the leaves of a seagrass. I. Pathway through epidermal and mesophyll tissues

Abstract

The apoplastic tracers Cellufluor and lanthanum nitrate were used at the light and electron microscope levels, respectively, to study the pathway taken by solutes from the water column through epidermal and mesophyll tissues in leaves of the seagrass Thalassodendron ciliatum (Forssk.) Den Hartog. Cellufluor penetrated walls of both epidermal and mesophyll cells within 4 h of exposure. For the next 20 h it continued to accumulate in epidermal and mesophyll walls, but to a greater extent in epidermal walls. Similar results were obtained with lanthanum nitrate. Heavy deposits of lanthanum frequently occurred in epidermal walls, as well as within extracytoplasmic spaces adjoining the highly invaginated plasmalemma of epidermal cells. The results suggest that the epidermis is an important site for absorption and that an unimpeded apoplastic pathway exists between epidermal and mesophyll tissues.