Characterization of Carrot Cell Wall Protein : I. EFFECT OF alpha, alpha'-DIPYRIDYL ON CELL WALL PROTEIN SYNTHESIS AND SECRETION IN INCUBATED CARROT DISCS

A single glycoprotein accounts for the majority of radioactivity secreted to the cell wall when incubated carrot (Daucus carota) discs are labeled with radioactive proline or arabinose. The ferrous chelator α,α′-dipyridyl prevents the synthesis of this protein. A new proline-labeled protein is made in the presence of α,α′-dipyridyl and is secreted to the cell wall. The protein has little, if any, carbohydrate attached to it and has a molecular weight of 55,000 daltons. This protein appears to be the nonhydroxylated, nonglycosylated form of the major cell wall glycoprotein. α,α′-Dipyridyl does not prevent proline label from becoming tightly (presumably covalently) bound to the cell wall, providing further evidence that hydroxylation and arabinosylation are not required for the covalent attachment of proteins to the cell wall. Messenger RNA extracted from incubated carrot discs produces a product which electrophoreses similarly to the protein made in the presence of α,α′-dipyridyl. The possible use of the carrot disc system to study gene structure and regulation is discussed.