Microphyll structure and chloroplast diversity in Selaginellaceae
| Autor: | Shau-Fu Li, 李紹輔 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 Selaginellaceae are a member of the Lycophyta. This family is monogeneric and cosmopolitan, having highly diverse species. The leaves of Selaginella are tiny with single veins and are termed microphylls. They contrast with megaphylls (usually larger with multiple veins) of other divisions of vascular plants. One novel trait, monoplastidy (one large chloroplast per photosynthetic cell), is only known in the vascular plant genus Selaginella. In contrast, the vast majority of vascular plants have many small chloroplasts per photosynthetic cell. However, the prevalence of monoplastidy and the association between it and morphological traits are unknown, and the ecophysiological implications are unclear. The aims of this study are to further explore the chloroplast traits and microphyll structures of Selaginella to better understand morphological features affecting adaptation to specific environments. Samples of 59 taxa of Selaginella (including a few herbarium specimens) collected from the Old- and New- World were studied using various techniques of microscopy to understand leaf structures and shape, number, size, and location of chloroplasts. Light environments of studied taxa were estimated from preliminary observations, field measurements and descriptions in local floras. Four native species in Taiwan were selected to obtain environmental data, including light intensity, temperature and humidity in their habitats during September 2012 to September 2014. In addition, a phylogeny tree constructed from plastid rbcL sequences from GenBank and collected materials were associated with the chloroplast traits. Based on leaf cell types and arrangements, eight leaf types of Selaginellaceae were delineated in this study. Leaf complexity varies between species, from simple fE(S) (thin leaf with funneled epidermal cell) type, with mainly two epidermal cell layers only, to EPS (Epidermis-palisade-spongy) or fEPS (funneled epidermal cell-palisade-spongy) type with palisade and spongy tissues differentiated. The leaves are typical microphylls, except mV (multiple veins) type with multiple veins. Based on the number of chloroplasts per dorsal epidermal cell, three chloroplast categories are delineated: (1) monoplastidy (M), (2) oligoplastidy (OL), and (3) multiplastidy (Mu). According to location, monoplastidy can be divided into ME (monoplastidy in dorsal epidermal cells), and MM (monoplastidy in mesophyll cells, but not in dorsal epidermal cells). In this study, 40 out of 59 taxa were found to have monoplastidy. Diversity of monoplastids includes cupped-shaped, bilobed, and giant disk-shaped. The giant disk chloroplast is a new type of monoplastid in Selaginella. The size of chloroplasts varies greatly, ranging from 3 to 26 µm in diameter. Most ME and MM species grow in deep shade environments. OL species grow in partial shade places. Mu species always grow in full sunlight or arid regions. Based on the results of phylogeny, leaf character and ecophysiology, the species of basal group Selaginella (e.g. S. deflexa) tend to have simpler leaf structures than other Selaginella species. Most species grow in the tropical and subtropical regions are dorsiventral, developing complex leaf structures. Mu was found in the most basal lineage (subgenus Selaginella), which suggests that the ancestral chloroplast condition in Selaginella is the typical condition for vascular plants, likely reflecting a common ancestor of all vascular plant chloroplasts. In contrast, M was found in some taxa of two subgenera (Gymnogynum and Stachygynandrum) indicated its derived status. Among ME species, 3 species with bizonoplasts might have evolved independently within subgenus Stachygynandrum. Hence, bizonoplast is a polytopic trait in this phylogeny. Selaginellaceae are one of the most ancient living vascular plant groups. Their novel chloroplast diversity, including various types of monoplastidy, which only occurs in Selaginella within vascular plants, may reflect is basal phylogenetic status maintaining plastid plasticity that has been lost in more derived groups. The strong association of monoplastidy with deep shade environments suggests that it may be an adaptation to deep shade. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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