Application of lanthanum and uranyl salts as tracers to demonstrate apoplastic pathways for transport in glands of the carnivorous plant Utricularia monanthos.

Lanthanum nitrate and uranyl acetate were used as opaque tracers in electron microscopy to demonstrate an apoplastic pathway within external and internal glands in the trap of the bladderwort Utricularia monanthos. Deposits of the tracers occurred in the cell walls but not in the protoplasts of intact cells. Cytochemical staining for polysaccharides showed that the tracers were confined to the non-impregnated regions of the wall. Only in the arms of quadrifids and bifids and the terminal cell of external glands an apoplastic pathway, extending from the external medium through the walls of the terminal cells and into the wall ingrowths of the pedestal cell, was demonstrated by the penetration of the tracers. The lateral cell wall of the pedestal cell is impermeable to the movement of tracers where it is completely impregnated. The routes that these apoplastic pathways might provide for water transport during the resetting of the trap are discussed.