Molecular visualization of pectin and DNA by ruthenium red

Apple fruit pectin was visualized in the electron microscope by the Kleinschmidt technique with Pt/Pd rotary shadowing, and also on benzalkonium-treated, especially thin carbon films using ruthenium red stain. Apple pectin molecules formed reticulate associations, which were partly dispersed after increasing the charge density of the molecules by enzymatic demethylation. Sycamore callus pectin molecules were visualized by the benzalkonium-ruthenium red technique as short rows of intensely electrondense dots, 3 nm across. Using the same technique, short sections of the ϕX174 RF DNA double helix were visualized and the existence of the B conformation in solution directly confirmed. These observations confirm the nature of chromotropism as indicated by physical studies and provide new evidence on the staining reactions of ruthenium red.