APOPLASTIC AND SYMPLASTIC PATHWAYS IN LEAVES AND ROOTS OF THE SEAGRASS HALODULE-UNINERVIS (FORSSK) ASCHERSP

The apoplastic tracers Cellufluor and lanthanum nitrate, and the symplastic tracer uranin, were used to study pathways for transport in leaves and roots of the seagrass Halodule uninervis (Forssk.) Aschers. An apoplastic pathway was shown to exist in most leaf tissues except in the region of the median vein where Casparian bands in bundle sheath cell walls prevented the penetration of the tracers into vascular tissues. Entry of uranin into leaf tissues was limited. The tracer remained in the protoplast of leaf epidermal cells and did not move symplastically into adjacent leaf tissues. Casparian bands in walls of root exodermal cells blocked further apoplastic movement of tracers into root tissues. In contrast, a symplastic pathway was shown to exist from the water column to the root cortex. The results are discussed in relation to the significance of apoplastic and symplastic transport in this seagrass.