Nodulation in Light- and Dark-grown Macrozamia communis L. Johnson Seedlings in Sterile Culture

The ability of aseptically cultured Macrozamia communis seedlingsto form apogeotropic root nodules in light and darkness wasexamined. In darkness, apogeotropic root nodules developed atthe junction of the primary-root and the cotyledonary node.More acropetally formed lateral-roots were not nodular and weretypical ageotropic or plagiotropic secondary-roots. When thesecultures were exposed to light, all of the roots became typical,apogeotropic cycad root nodules. Light stimulated dichotomousbranching of nodules previously formed in the dark. Nodulesexposed to light were more papillose than those maintained indarkness. Light also inhibited primary and secondary-root elongation. Macrozamia communis, cycad apogeotropism, dichotomous branching, light induction, root nodulation sterile culture