Ligule development and fine structure in two heterophyllous species of Selaginella

Abstract

Ligules of Selaginella pilifera and S. uncinata were studied by light and electron microscopy. These ligules can be anatomically divided into tip, neck, and basal regions. The upper part of the ligule base is composed of very dense polygonal cells containing many ribosomes, endoplasmic reticulum (ER), and Golgi bodies. In S. pilifera, callose-like walls are secreted around these cells. The lower part of the base consists of wedge-shaped glossopodial cells and the adjacent two layers of sheath cells. Transfer-cell-like walls separate the glossopodium and upper sheath layer, whereas walls containing prominent plasmodesmata separate the two sheath layers. A continuous cuticle covers the entire ligule. During early ontogeny, all ligule cells are highly RNA positive, whereas later only the polygonal base cells stain densely. The anatomy and development of the ligule suggest that it is an active structure. The results of this study are compared with previous studies, especially in relation to ligular function.

Micromorphology of outer exospore coatings inSelaginellamegaspores

“…A number of researchers have studied the genus from different viewpoints, ranging from anatomical (Hebant & Lee, 1984) and morphological (Lyon, 1901;Horner & Arnott, 1963;Horner et al 1975;Dengler, 1983;Page, 1989;Webster, 1992) to palaeobotanical (Bek et al 2001;Cottnam et al 2000) and most recently to phylogenetic and taxonomic investigations (Korall et al 1999;Korall & Kenrick, 2002). Phylogenetic analyses of DNA sequence data agree that Lycophytes (including Selaginella, Isoetes Linnaeus and Huperzia Bernardi) form a distinct clade, branching off from other tracheophytes early in land plant evolution (Pryer et al 2001, Quandt et al 2004).…”

Comparative Morphology of the Glossopodia of Three North American Isoetes Ligules

“…Ligule ontogeny is also dissimilar between Selaginella and Isoetes. In Selaginella the ligule develops from two rows of superficial cells (Smith, 1900a;Horner et al, 1975;Gifford and Foster, 1989), whereas the Isoetes ligule originates from a single epidermal cell (Smith, 1900a;Bhambie, 1963;Sporne, 1966;Gifford and Foster, 1989). In both, the ligules are attached to the adaxial leaf surface just distal to the sporangium, produce callose, achieve maturity before their corresponding leaves, and both lack chlorophyll, starch, and intercellular spaces (Smith, 1900a;Bierhorst, 1971;Horner et al, 1975;Jagels and Garner, 1979;Kristen and Biedermann, 1981;Webster, 1992).…”

Physiological anatomy and function of the membranous grass ligule

“…Unlike the grass ligule, there has been sustained interest in, and debate surrounding, the function of these organs over the past 25 yr (e.g. Sigee, 1974Sigee, , 1975Sigee, , 1976Horner et al, 1975 ;Kristen & Biedermann, 1981 ;Kristen et al, 1982 ;Bilderback, 1987). Although an in-depth review of lycopsid ligule biology is beyond the scope of this article, some comments about these organs are warranted in so far as they relate to grass ligule biology.…”

“…Although an in-depth review of lycopsid ligule biology is beyond the scope of this article, some comments about these organs are warranted in so far as they relate to grass ligule biology. The information on lycopsid ligules is summarized from accounts in Sigee (1974Sigee ( , 1975Sigee ( , 1976, Horner et al (1975), Kristen & Biedermann (1981), Kristen et al (1982), and Bilderback (1987). Table 4 summarizes some of the salient features of the ligules of Selaginella and Isoetes and compares them with the membranous ligule of Lolium.…”

“…Table 4 summarizes some of the salient features of the ligules of Selaginella and Isoetes and compares them with the membranous ligule of Lolium. The published electron microscope studies on the ligule of Selaginella (Sigee, 1974(Sigee, , 1975(Sigee, , 1976Horner et al, 1975) conclude that, although ultrastructurally it appears to be highly active in synthesis of polysaccharides, it is not secretory, but may represent a vestigial structure which once was secretory. However, this view is contradicted by the light microscope study of Bilderback (1987) who suggested that the Selaginella ligule ' may be glandular ' in view of the association of ' mucilage bodies ' near the ligule in the axils of the leaves.…”