Structure and Function of the Root Cap of Lolium temulentum L. (Poaceae): Parallels with the Ligule

Structure of the root cap ofLolium temulentum L. and of thechemistry of its secretory product were investigated with conventionaltransmission electron microscopy, zinc iodide–osmium tetroxideimpregnation, and use of protein and polysaccharide localizationtechniques at the ultrastructural level. Structural and functionalinformation concerning the root cap is compared with that previouslyobtained for the membranous ligule of this species. Similaritiesbetween root cap cells and adaxial epidermal cells of the liguleare described and discussed. It is concluded that both systemsare secretory and represent a similar response to the commonproblem of easing the passage of growing organs against thesoil or other plant parts. Darnel; Gramineae; grasses; ligule; Lolium temulentum L.; Poaceae; root cap; secretion; ultracytochemistry; ultrastructure; zinc iodide-osmium tetroxide impregnation