Diversity of silica bodies on microphylls of Selaginellaceae

• Main Authors: Tzu-Yun Lee, 李紫昀
• Other Authors: Chiou-Rong Sheue
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/295979

碩士 === 國立中興大學 === 生命科學系所 === 107 === Silicon (Si) is the second abundant element on the earth surface. Silicate minerals can be weathered and release silicic acid (H4SiO4). Plants take up silicic acid and precipitate it as biogenic silica structures named phytoliths. It has been shown that Equisetum, Poaceae and Cyperaceae have been proved that they can precipitate Si inside cells or on cell walls. Different forms of silica bodies were also found in bryophyte, lycophyte, and ferns. We still have poor understanding and very little information of silica bodies of Selaginellaceae, although a few species had been studied. This is the first systematic study of silica bodies on microphylls of Selaginellaceae. The aims are to explore the diversity of silica bodies, to evaluate their taxonomic value, and to understand find the relationships between silica bodies and phylogeny in Selaginellaceae. Selaginella is the only genus in Selaginellaceae (Lycophyta) which comprises ca. 800 species in the world. In this study, 76 Selaginella taxa, nearly one-tenth species of Selaginella collected from America, Europe, Asia, Australia, and Hawaii were studied. Healthy and mature leaves (microphylls) were detached and cleaned before various microscopic observations. The forms and patterns (on leaves surface) of silica bodies were observed by scanning electron microscope. Free hand sections were conducted to confirm the deposition site and forms of silica bodies. The 3D models of silica bodies were constructed by atomic force microscope (AFM), and the content of composition elements of silica bodies were measured by an energy dispersive X-ray spectrometer (EDS)Last, the relationships between silica bodies and the phylogenetic tree of Selaginellaceae constructed from chloroplast rbcL sequences were assessed. A total of 74 out of the 76 species of Sellaginella studied were found to have silica bodies found on their leaf surfaces. The results show that silica bodies are one of the general features of Selaginella. Following to the International Code for Phytolith Nomenclature, 10 forms of silica bodies in Selaginella were identified. They are papillae, light-protruded papillae, granular, thin-tabular, conical, reniform, rondel, acicular, sinuate carinate and marginal long cell wall with silicon. The results of EDS proved that the peglike projections on leaves of Selaginella are silica bodies. Most of silica bodies contain more then 10% of silicon, but silicon contents of papillae, light-protruded papillae, and thin-tabular silica bodies are less than 10%. Among them, the silicon content of granular silica bodies varies greatly (0.05-22.32%), and papillae silica bodies have the lowest content of silicon (0.93-5.08%). There are eight arrangements of silica body on one epidermal cell, and nine patterns of silica bodies on Selaginella leaves were delineated. Generally very few silica bodies or no silica bodies distributed on the ventral side of dorsal leaves in most Selaginella species with anisophylls. The pattern of conical silica bodies scattered along cell margins of an epidermal cell were only can found in resurrection Selaginella. Silica bodies can be found in all of six common cell types (isodiametric cell, elongated cell, marginal long cell, idioblast, trichome, and few guard cells) of Selaginella, but guard cells only deposit silicon (without specific projections). For the Selaginella species living in sun exposed environments (mostly non-dorsiventral, isophyllous), acicular, conical and thin-tabular silica bodies are their major silica bodies. In contrast, the Selaginella species (all dorsiventral leaves and anisophllous) growing in the understorey of forests (less sunlight) have high diversity of forms of silica bodies (10 forms). There are no relations between the character of silica bodies and plant morphology (creeping or erect) of Selaginella. Unexpectedly, an unusual stomatal type, marginal stomata, was commonly observed in the species living in extreme humid environments (water fall, stream and wet cliff). The result shows that there are no silica bodies in the subgenus Selaginella (Selaginella deflexa) and some of the subgenus Ericetorum (S. gracillima). Since these they are the basal group of this family, it implies that the ancestors of Selaginella might not have silica bodies. In addition, the species with close relationship usually contain similar forms of silica bodies, but there are no relations between patterns of silica bodies (on leaves) and phylogeny of Selaginella. This study has revealed high diversity of silica bodies of Selaginella and confirmed these traits are stable and species-specific. The characters of silica bodies have high taxonomic value to be an aid for solving the identification challenge of Selaginellaceae. Moreover, the change of ability of silicon deposition of Selaginella species during the past 350 million years it is uncovered. A close relation between the forms of silica bodies and light environments implies that the possible optical effects of silica bodies of Selaginella are worthy to explore.