Endodermis-like sheaths in the submerged freshwater macrophyte Ranunculus trichophyllus Chaix

Light, fluorescence and electron microscopical analysis of the rooted fresh water plant Ranunculus trichophyllus revealed a peculiar anatomical feature . In addition to the true endodermis encircling the root stele, endodermis- like sheaths occurred around each vascular bundle of the leaf segments and of the eustelic stem with its large central cavity, which assumed an anatom ical feature resembling that of some pteridophyte stems. These impermeable sheaths, whose cells differentiate suberized walls, can play a major role i n hampering the apoplastic leakage of the pressurized water solution which flows throughout the plant in xylem vessels and contains the mineral nutrie nts taken up by the roots from the sediment. Moreover, these sheaths can fu nction in preventing flooding of the aerenchymatic cavities of the submerge d organs. In this way the endodermis-like sheaths preserve the correct circ ulation of gas and nutrient solution through the entire organism and assume great significance as a structural mechanism evolved by this species to su rvive and grow underwater. (C) 1998 Annals of Botany Company.