| Co-Investigator(Kenkyū-buntansha) |
KATO Masahiro National Museum of Nature and Science, Japan, Dept. of Botany, Director (20093221)
HASEBE Mitsuyasu National Institute for Basic Biology, 基礎生物学研究所, Prof (40237996)
FUJII Noriyuki Kumamoto Univ., 理学部, Associate Prof (40305412)
NISHIDA Sachiko Nagoya Univ. Museum, Museum, Assistant Prof (10311490)
WATANABE Yasunori Rissho Univ., Fac. of Sci., Prof (20112477)
喜多 陽子 日本女子大学, 理学部, 学術研究員 (60345262)
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| Budget Amount *help |
¥42,250,000 (Direct Cost: ¥32,500,000、Indirect Cost: ¥9,750,000)
Fiscal Year 2007: ¥7,020,000 (Direct Cost: ¥5,400,000、Indirect Cost: ¥1,620,000)
Fiscal Year 2006: ¥8,580,000 (Direct Cost: ¥6,600,000、Indirect Cost: ¥1,980,000)
Fiscal Year 2005: ¥10,660,000 (Direct Cost: ¥8,200,000、Indirect Cost: ¥2,460,000)
Fiscal Year 2004: ¥15,990,000 (Direct Cost: ¥12,300,000、Indirect Cost: ¥3,690,000)
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| Research Abstract |
Podostemaceae is an aquatic angiosperm that is growing on the rock surface in the river or waterfall. They are subjected to rushing water in the rainy season and exposed in the air in the dry season. The family is widespread in pan-tropic regions all over the world. Because of their peculiar morphology, Podostemaceae plants have been paid much attention since the late 1800s. Recent molecular phylogenetic analyses using cpDNA (e.g. mat K) clearly shows that Podostemaceae belongs to the eudicots, and is close to Classulaceae. Therefore, the peculiar shape of plant body seems to have evolved as a result of adaptation to unique habitats, by so-called saltational evolution. We aimed to clarify the evolutionary history and the mechanism underlying the saltational evolution of Podostemaceae. We conducted botanical expeditions in Africa, Madagascar, South America, and Asia to collect genera of Podostemaceae, and examined them by the comparative development among Podostemaceae genera, the molec
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ular phylogenetic analysis, the molecular genetic analysis, and the am-physiological analysis. The Phylogenetic analysis showed that American, African and Asian Podostemaceae each form monophyletic groups, and their distributions are narrow and local In contrast, Tristicha trifaria (subfamily Tristichoideae) is exceptionally widespread through America and Africa. Our examination suggested that Tristicha trifaria was originated from West Africa (Cameroon), and dispersed to many tropical areas excluding Asia. On the other hand, comparative development clearly showed that the shoot apical meristem (SAM) is totally lacking in Podostemoideae, and leaf primordia arise from the older leaf base associated with cell retardation and separation. This process is similar to the programmed cell death. The other subfamily, Tritichoideae, sister to subfamily Podostemoideae, has SAM typical of angiosperms, and it is supposed that SAMs were missing drastically when Podostemoideae evolved from Tristichoideae. To examine whether the SAM was lost morphologically or genetically, we extracted STM homologous-, WUS homologous-, and CLV3 homologous-genes, three of which are detected in the SAMs of Arabidopsis (a model angiosperm plant). We are now carrying out the in situ hybridization method to detect those homologous genes in the expected area of leaf primordium formation. Eco-physiologically, it was shown that the photosynthetic activity of Podostemaceae flattened or thalloid roots was the highest in the depth of 20cm from the water surface, suggesting that the plant body growing near the water surface is damaged by extensive sunlight. It is interesting to share the photosynthetic behavior with other planktons that lives in water. The epidermal cells interestingly have two types of chloroplasts with quite different sizes, i.e. the very small and the very large ones, in Podostemoideae. The small chloroplasts are located near the upper wall in the epidermal cell, and the large near the bottom wall of the cell, both of which are located side by side with no open space. It seems likely that the small chloroplasts near the upper wall act as barrier of extensive sunlight. Less
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