Suspension-cultured endosperm cells from L. multiflorum secrete into the medium an arabinogalactan-protein in which the protein moiety is rich in hydroxyproline. When cells are grown in the presence of proline labelled with 14C or 3H, the imino acid is rapidly removed from the medium and radio- activity can subsequently be detected in extracellular trichloracetic acid-soluble, ethanol-insoluble material. In this fraction, which contains the arabinogalactan-protein and other polysaccharides, radioactive label is distributed between proline and hydroxyproline. α,α'-Dipyridyl, a chelator of ferrous ion, has no effect on the total radioactivity secreted but markedly alters the distribution of radioactivity in favour of peptidyl proline. Although this inhibition of peptidyl proline hydroxylation can be reversed by ferrous or zinc ions, it is not possible to conclude that ferrous ion, which is required for hydroxylation in other systems, participates specifically in the reaction in ryegrass endosperm cells. Concomitant with the inhibition of proline hydroxylation, α,α'-dipyridyl suppresses the biosynthesis or secretion of extracellular arabinogalactan-protein and arabinoxylan.
Gene expression analyses reveal metabolic specifications in acute O2-sensing chemoreceptor cells
