MICROSCOPIC OBSERVATIONS OF THE IRON PLAQUE OF A SUBMERGED AQUATIC PLANT (VALLISNERIA-AMERICANA MICHX)

The immediate interface between the root cell wall and the iron plaque of Vallisneria americana Michx (wild celery), a submerged freshwater plant collected in lakes of the St. Lawrence River system, Quebec, Canada, was examined. Based on transmission electron microscope observations and X-ray diffraction data, the iron plaque of V. americana is composed mainly of amorphous Fe material (occurring as filaments and dispersed material) and some crystalline particles (needles and nodules) composed of goethite and/or lepidocrocite. Energy dispersive spectroscopy also revealed the presence of Mn-rich particles in the plaque. Impurities, such as quartz and clays, were present inside the root iron coating, as were micro-organisms (bacteria) which are postulated to play an indirect role in the deposition of iron oxyhydroxides on the root.