The Occurrence of Synaptonemal Complexes in the Slime Mold Echinostelium Minutum De Bary

Elongate tripartite structures termed synaptonemal complexes have been observed during meiotic prophase in a number of sexually reproducing animals and plants (5, 10, 11, 12, 13, 17) . A complex seen in longitudinal section ("frontal view," 14) appears as three parallel strands . Apparently this triple-stranded structure forms along the entire length of synapsed homologous chromosomes and is a concomitant of chiasma formation and crossing over (4, 13, 14, 15) . On the basis of cytochemical observations it is generally agreed that the synaptonemal complex is composed of protein and nucleic acid (4, 14) . Both DNA (4) and RNA (21) have been reported as components; however, conclusions regarding their presence and localization are inconsistent . The synaptonemal complex is a valuable indicator of meiosis in studies of the life histories of organisms with minute chromosomes such as myxomycetes. That the postcleavage spore is the site of meiosis in the life histories of four of the five orders of the subclass Myxogastromycetidae (9) is indicated by synaptonemal complexes demonstrated by ultrastructural studies (1, 3) . In this report we present the first description of normal and anomalous synaptonemal complexes (14) in a species of the Echinosteliales . The arrangement of the anomalous synaptonemal complexes with the biphasic nucleolus of Echinostelium minutum de Bary has to the best of our knowledge not been previously observed in any member of the Protista .