Seed reserves and early symbiotic protocorm development of Platanthera hyperborea (Orchidaceae)

Seeds of the terrestrial orchid Platanthera hyperborea consist of a thin testa and a simple embryo without a cotyledon. Epidermal and parenchyma cells of the embryo contained lipid and protein as storage reserves. Many of the protein bodies had globoid crystals identified by their P, Ca 2+ , Mg 2+ , and K + content. Germination occurred with either Rhizoctonia cerealis or Ceratorhiza goodyerae-repentis as the fungal symbiont on Warcup's medium. The fungus entered through dead suspensor cells and triggered protocorm development and concomitant utilization of lipid and protein reserves. Fungal hyphae formed pelotons with protocorm cells initially, and these went through stages of vacuolation and collapse. Some hyphae stored small numbers of polyphosphate bodies. Clumps of degenerated hyphae were usually encased within material that stained positive with aniline blue, presumably callose.