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

Abstract

Si deposits in the endodermis of the seminal root of Sorghum bicolor (L.) Moench., following culture in nutrient solution containing 100 ppm SiO₂ for 7 days, were investigated by transmission electron microscopy. Si microassay was carried out by means of the EMMA-4 system. Endodermal ultrastructure is discussed. EM micrographs of the Si deposits reveal information regarding their formative processes and indicate a considerable involvement with the cellulosic structure of the inner tangential wall (ITW). The initial deposits are believed to be composed structurally of particles designated as primary spherical units. The EMMA-4 conclusively indicated that Si was localized and confined to the ITW, and the implications of this result for previous studies are considered. Current evidence from studies of endodermal function, as well as root translocation physiology, is utilized in arriving at tentative mechanisms for silicic acid transport and subsequent Si deposition on the ITW.