Pectin‐protein Interaction as a Basis for Auxin‐induced Alteration of Protein Heat Coagulability

G alston , A rthur W., R avindar K aur , N irmala M aheshwari , and S atish C. M aheshwari . (Yale U., New Haven, Conn.) Pectin‐protein interaction as a basis for au xin‐induced alteration of protein heat coagulability. Amer. Jour. Bot. 50(5): 487–494. Illus. 1963.—The in vivo administration of 2,4‐D or other auxins to etiolated or green pea stem sections results in a decreased heat coagulability of the macromolecular components of the particle‐free cytoplasm of these tissues. Addition of auxin to homogenates is without effect. Gibberellins alone are also without effect, but may enhance the in vivo action of auxin. The altered heat coagulability may become apparent as soon as 4–6 hr after auxin administration, though longer induction periods are sometimes necessary. The auxin eff'ect is prevented by general metabolic inhibitors and most effectively by ethionine, whose inhibitory action is completely reversed by methionine. Electrophoresis on paper and on starch revealed no major differences between the proteins of control and auxin‐treated stems. Approximately 90% of the weight of the heat coagulum can be accounted for as protein; small quantities of nucleic acids, lipids, polysaccharides and pectins are also present. The “soluble pectin” content of the homogenate before heat coagulation is at least doubled by auxin treatment. This increase is also inhibited by ethionine, whoso effect is annulled by methionine. Addition of citrus pectin to control homogenates stabilizes the proteins against heat coagulation. It thus appears likely that the effect of auxin on the heat coagulability of the cytoplasmic proteins can be explained through effects on the metabolism of the materials which have been called “cold‐water‐soluble pectins.”