The Ultrastructure and Electron-probe Microassay of Silicon Deposits in the Endodermis of the Seminal Roots of Sorghum bicolor (L.) Moench

Si deposits in the endodermis of the seminal root of Sorghumbicolor (L.) Moench., following culture in nutrient solutioncontaining 100 ppm SiO₂ for 7 days, were investigated by transmissionelectron microscopy. Si microassay was carried out by meansof the EMMA-4 system. Endodermal ultrastructure is discussed. EM micrographs of theSi deposits reveal information regarding their formative processesand indicate a considerable involvement with the cellulosicstructure of the inner tangential wall (ITW). The initial depositsare believed to be composed structurally of particles designatedas primary spherical units. The EMMA-4 conclusively indicated that Si was localized andconfined to the ITW, and the implications of this result forprevious studies are considered. Current evidence from studies of endodermal function, as wellas root translocation physiology, is utilized in arriving attentative mechanisms for silicic acid transport and subsequentSi deposition on the ITW.