LOCALIZATION OF CELL-WALL PROTEINS IN RELATION TO THE DEVELOPMENTAL ANATOMY OF THE CARROT ROOT APEX

A panel of monoclonal antibodies that recognize a class of cell wall proteins, related to the hydroxyproline-rich glycoproteins, has been assembled and characterized in relation to their restricted patterns of binding amongst the cells comprising the carrot root apex. The occurrence of the epitopes at the surface of cells and intercellular spaces in the region of the apex between the meristematic initials and the region of cell expansion indicates dynamic patterns that reflect aspects of the development of the anatomical pattern. The monoclonal antibody JIM11 reacts with the surface of cells in the central root cap and the region of the meristem. As the cortex/stele boundary becomes established the reactivity is seen in the inner cortical layers and finally in the whole cortex. Later in development the JIM11 epitope is also expressed by two pairs of pericycle cell files adjacent to the phloem region and also by the epidermis. The JIM12 monoclonal antibody is unreactive with cells in the region of the root cap and the meristem but is reactive with intercellular spaces formed at the junction of the oblique and radial walls in the double-layered sectors of the pericycle opposite the xylem poles. This epitope is also transiently expressed by the two phloem sieve tube element mother cells. Later in development JIM12 recognizes the future metaxylem cells. The antibody JIM20 recognizes all the cells and intercellular spaces recognized by JIM11 and JIM12. Immune-chemical analyses indicate crossreactivity with carrot taproot extensin and Solanaceous lectins.