Fine Structure of the Cell Wall of Carrot Parenchyma Revealed by Quick-Freeze, Deep-Etch Electron Microscopy.

The cortical parenchyma cell wall of the naturally grown carrot root was investigated using quick-freeze, deep-etching electron microscopy. The primary cell wall consisted of numerous fibrous components about 10 nm in diameter, and granular components around and among the fibrous components. When the tissue was treated with polygalacturonase, the granular components were digested away from the cell wall, and the fibrous components in the disordered alignment remained. The granular components might be of pectic substances and have a cementing role among the fibrous components. The middle lamella was formed by the fibrous, reticular and granular substances. A calcium-induced pectic gel showed a reticular structure composed of fibrillar materials 3 to 15nm in diameter. This suggests that the fibrous components are considered to contain the fibrillar type of pectic substances. When the tissue was treated with polygalacturonase, a meshwork structure still remained in the middle lamella and the intercellular space located at the tricellular junction, where a crossed-layered structure of the meshwork was observed and remained even after the tissue was boiled for 30 min before the enzyme treatment. These facts suggest that the pectic substances might not contribute to the meshwork structure in the middle lamella. [ABSTRACT FROM PUBLISHER]