碩士 / 國立嘉義大學 / 生物資源學系研究所 / 100 / The Begoniaceae are dicotyledonous angiosperms. To date, more than 1600 species have been described. The Begoniaceae have two genera, Begonia and Hillebrandia, but Hillebrandia has only a monotypic species, H. sandwicensis. This species-rich family displays high diversity of leaf morphology, and contains many members with remarkable variegated leaves. Thus, the members of Begoniaceae provided ideal materials for this study, which investigated leaf structure and the mechanism of foliar variegation, with implications for ecology and taxonomy in 55 species belonging to 22 sections of Begonia and H. sandwicensis. In addition, a novel plastid, the iridoplast, was studied. This plastid was reported in B. pavonina previously, and was thought to be associated with the phenomenon of iridescence. This study characterized structural features of iridoplasts and asked whether they occur generally in the Begoniaceae.
There are two types of adaxial epidermal cells in Begoniaceae leaves: lens-shaped and flat. The uppermost cell layer of the mesophyll tissue of Begoniaceae leaf is not palisade as occurs generally in dicots. Instead, they are funnel-shaped chlorenchyma. One to eight layers of water storage cells are present between the epidermal and funnel-shaped chlorenchyma on both sides in succulent leaves of Begonia. Observations of leaf development of B. fenicis clarified the origin of water storage cells. The water storage cells are derived from protoderm, and are part of the hypodermis. They are not part of multiple epidermal layers as reported previously.
The leaf structure of Begoniaceae is dorsiventral. Based on the presence or absence of water storage cells, the number of layers of water storage cells, and the size of the epidermal cells, three types of leaf structure are defined. In these definitions, the mesophyll defines the center of the leaf: (1) symmetric, with equal layers of water storage cells on each side in (a) one layer or (b) two layers; (2) asymmetric, with unequal layers of water storage cells on the two sides of the leaf, more layers on (a) the adaxial side or (b) the abaxial side; (3) the absence of water storage cells, divided into two subtypes defined by the relative epidermal cell size on the two sides of the leaf, (a) symmetric, with equal epidermal cell size on each side; (b) asymmetric, with larger epiderminal cells on the abaxial side.
Seven species of Begonia with various foliar variegation patterns were examined to reveal their variegation mechanism and consequent effect on photosynthesis. In the green area of a leaf, funnel-shaped cells are in tight contact with adaxial epidermal cells or water storage cells. In the light area of a leaf, intercellular spaces are commonly found between funnel-shaped cells and adaxial epidermal cells or water storage cells. The chloroplasts from both green and light areas of the leaves of Begonia did not show any observable differences, and the maximum quantum yields of photosynthesis system II (PSII) also did not differ significantly between these two areas. In addition, a cultivar Ficus pumila‘Sonny’(chlorophyll type variegation) was studied as a contrast with Begonia. Only protoplastids were found in white areas of Ficus leaves. The maximum quantum yields of PSII were close to zero in these areas. In addition, variegated young leaves of Blastus cochinchinensis Lour. (Melastomataceae) were observed, but no consistent characteristics of leaf structure were found to be related to variegated leaves. More study of variegated young leaves of this taxon is needed in the future.
The chloroplasts in mesophyll tissue are the main location for photosynthesis in most green plants. However, in 34 species of Begoniaceae chloroplasts were also found in the leaf epidermal cells in this study. However, based on ultratructural characteristics, two types of novel chloroplasts in adaxial epidermal cells were recognized: (1) an iridoplast (3 – 11 μm long): elongated oval- shaped, with no typical grana, but groups of 3 – 4 layers of stacked thylakoid membranes continuously parallel to the long axis of the plastid, (2) a small chloroplast (2 – 4 μm long), similar to a normal chloroplast, with thylakoid membranes and grana.
In order to know whether these special chloroplasts occur in abaxial epidermal cells, six species of Begonia with iridoplasts were observed. Only small chloroplasts were found in the abaxial epidermal cells. In addition, three shade-adapted species of Melastomataceae (Blastus cochinchinensis Lour., Bredia hirsuta Bl.var. rotundifolia (Liu & Lu) S. F. Huang & T. C. Huang and Pachycentria formosana Hayata) were observed, especially for this novel chloroplast. All of them were found to possess small chloroplasts in their adaxial epidermis.
The leaf structural characteristics of Begoniaceae revealed in this show no consistent characteristics within a section. Instead, leaf structure is related to habitat. For example, the species growing under strong light and dry environment tends to have flat adaxial epidermal cells and well developed water storage cells in leaves. Species with the funnel-shaped chlorenchyma, and chloroplasts in the chlorenchyma with well developed grana are typically shade plants. The mechanism of foliar variegation in Begonia is the air space type (structural variegation). In a cultivar of Begonia, it is reported here for the first time a variation on structural variegation where the intercellular space is located between water storage tissue and the top layer of the chlorenchyma. Either iridoplasts or small chloroplasts are found in adaxial epidermal cells in all Begoniaceae species in this study, but these two types of chloroplast appear in adaxial epidermal cells of different species. Some species, however, have iridioplasts in the adaxial epidermis and small chloroplasts in the abaxial epidermis. The notion that iridoplasts and iridescence are associated with each other is challenged by this study, as iridoplasts were found in 18 Begonia taxa but only one of this showed iridescence.
| Identifer | oai:union.ndltd.org:TW/100NCYU5404004 |
| Creators | 包尚弘 |
| Contributors | Chiou-Rong Sheue, Chiung-Ru Yang, 許秋容, 楊瓊儒 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 0 |
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