屋久島における標高傾度に沿った土壌窒素・リン可給性の相互作用を介した土壌－植生系の分化

京都大学0048新制・課程博士博士(農学)甲第21968号農博第2358号新制||農||1070(附属図書館)学位論文||R1||N5219(農学部図書室)京都大学大学院農学研究科地域環境科学専攻(主査)教授 北山 兼弘, 教授 小杉 緑子, 教授 舟川 晋也学位規則第4条第1項該当Doctor of Agricultural ScienceKyoto UniversityDGA

Leaf trichomes in Metrosideros polymorpha can contribute to avoiding extra water stress by impeding gall formation

Background and Aims: Plants inhabiting arid environments tend to have leaf trichomes, but their adaptive significance remains unclear. Leaf trichomes are known to play a role in plant defence against herbivores, including gall makers. Because gall formation can increase water loss partly through increased surface area, we tested the novel hypothesis that leaf trichomes could contribute to avoiding extra water stress by impeding gall formation, which would have adaptive advantages in arid environments. Methods: We focused on Metrosideros polymorpha, an endemic tree species in the Hawaiian Islands, whose leaves often suffer from galls formed by specialist insects, Hawaiian psyllids (Pariaconus spp.). There is large variation in the amount of leaf trichomes (0–40 % of leaf mass) in M. polymorpha. Three gall types are found on the island of Hawaii: the largest is the ‘cone’ type, followed by ‘flat’ and ‘pit’ types. We conducted laboratory experiments to quantify the extent to which gall formation is associated with leaf water relations. We also conducted a field census of 1779 individuals from 48 populations across the entire range of habitats of M. polymorpha on the island of Hawaii to evaluate associations between gall formation (presence and abundance) and the amount of leaf trichomes. Key Results: Our laboratory experiment showed that leaf minimum conductance was significantly higher in leaves with a greater number of cone- or flat-type galls but not pit-type galls. Our field census suggested that the amount of trichomes was negatively associated with probabilities of the presence of cone- or flat-type galls but not pit-type galls, irrespective of environmental factors. Conclusion: Our results suggest that leaf trichomes in M. polymorpha can contribute to the avoidance of extra water stress through interactions with some gall-making species, and potentially increase the fitness of plants under arid conditions

Synthesis of a Novel Pyrazine-Pyridone Biheteroaryl-Based Fluorescence Sensor and Detection of Endogenous Labile Zinc Ions in Lung Cancer Cells

A small extent of endogenous labile zinc is involved in many vital physiological roles in living systems. However, its detailed functions have not been fully elucidated. In this study, we developed a novel biheteroaryl-based low molecular weight fluorescent sensor, 3-(phenylsulfonyl)-pyrazine-pyridone (5b), and applied it for the detection of endogenous labile zinc ions from lung cancer cells during apoptosis. The electron-withdrawing property of the sulfonyl group between the phenyl ring as an electron donor and the pyridone ring as a fluorophore inhibited the intramolecular charge transfer state, and the background fluorescence of the sensor was decreased in aqueous media. From the structure-fluorescence relationship analysis of the substituent effects with/without Zn 2+ , compound 5b acting as a sensor possessed favorable properties, including a longer emission wavelength, a large Stokes shift (over 100 nm),a large fluorescence enhancement in response to Zn 2+ under physical conditions, and good cell membrane permeability in living cells. Fluorescence imaging studies of human lung adenocarcinoma cells (A549) undergoing apoptosis revealed that compound 5b could detect endogenous labile zinc ions. These experiments suggested that the low molecular weight compound 5b is a potential fluorescence sensor for Zn 2+ toward understanding its functions in living systems

Feeding behaviour and digestion physiology in larval fish – current knowledge and gaps and bottlenecks in research

Food uptake follows rules defined by feeding behaviour that determines the kind and quantity of food ingested by fish larvae as well as how live prey and food particles are detected, captured and ingested. Feeding success depends on the progressive development of anatomical characteristics and physiological functions and on the availability of suitable food items throughout larval development. The fish larval stages present eco-morpho-physiological features very different from adults and differ from one species to another. The organoleptic properties, dimensions, detectability, movements characteristics and buoyancy of food items are all crucial features that should be considered, but is often ignored, in feeding regimes. Ontogenetic changes in digestive function lead to limitations in the ability to process certain feedstuffs. There is still a lack of knowledge about the digestion and absorption of various nutrients and about the ontogeny of basic physiological mechanisms in fish larvae, including how they are affected by genetic, dietary and environmental factors. The neural and hormonal regulation of the digestive process and of appetite is critical for optimizing digestion. These processes are still poorly described in fish larvae and attempts to develop optimal feeding regimes are often still on a ‘trial and error’ basis. A holistic understanding of feeding ecology and digestive functions is important for designing diets for fish larvae and the adaptation of rearing conditions to meet requirements for the best presentation of prey and microdiets, and their optimal ingestion, digestion and absorption. More research that targets gaps in our knowledge should advance larval rearing

Influences of Forest Management on the Functional Diversity of Soil Microbial Decomposition

本研究では，人間の管理によって変化した樹木種の多様性が，土壌微生物の分解機能の空間的多様性にどのような影響を与えるのかについて，京都周辺の3つの森林（常緑広葉樹林，里山林，ヒノキ林）を比較して評価した．各森林から表層土壌を一定間隔で10コア採取し，コア毎に土壌懸濁液を作成し，31種類の有機物が基質として含まれるエコプレートに添加して25度で96時間培養し，土壌微生物による基質の分解度を吸光度を用いて測定した．得られた30コア×31有機物分解度のマトリクス・データに，主成分分析を適用して，コア間の分解機能のばらつきを評価した．樹木種多様性は，常緑広葉樹林＞里山林＞ヒノキ林の順に低下した．主成分分析の結果，常緑広葉樹林と里山林に比べて，単一樹種のヒノキ林では分解機能のコア間のばらつきが有意に小さかった．以上の結果は，樹木種多様性の著しい低下が土壌微生物の分解機能の空間的多様性の低下を引き起こすことを示唆した．森林の生物多様性を守るために，森林管理を行う際には地上部の多様性のみならず，地下部の多様性にも目を向ける必要がある． In this study, we investigated if/how reduced tree-species diversity due to human interference affects the spatial variability of soil microbial activities by comparing three forest types, which commonly occur in Kyoto (i.e. evergreen broad-leaved forest, satoyama forest, and hinoki-cypress plantation). We collected ten soil cores from the topsoil at regular intervals in each forest. Soils from each core were diluted 100 times in extracting solution and suspended solids were inoculated to a piece of the Biolog EcoPlate, which contains 31 types of organic compounds for microbial community profiling. Inoculated EcoPlates were incubated at 25°C for 96 hrs. Decomposability of each organic compound was assayed by reading spectral absorbance. A principal component analysis (PCA) was applied to the derived data matrix consisting of 30 cores and 31 compounds. Tree species richness decreased in the order of evergreen broad-leaved forest > satoyama forest > hinoki plantation. Results of PCA indicated that the variability among cores was significantly reduced in the hinoki forest than in the other two forests. This suggests that the spatial variability of soil microbial communities/activities is significantly reduced under the mono-specific canopy of the hinoki forest. Because soil microbial communities are an important aspect of biodiversity in a forest ecosystem, microbial diversity needs to be taken into account for better managing those forests

Demography and selection analysis of the incipient adaptive radiation of a Hawaiian woody species

Ecological divergence in a species provides a valuable opportunity to study the early stages of speciation. We focused on Metrosideros polymorpha, a unique example of the incipient radiation of woody species, to examine how an ecological divergence continues in the face of gene flow. We analyzed the whole genomes of 70 plants collected throughout the island of Hawaii, which is the youngest island with the highest altitude in the archipelago and encompasses a wide range of environments. The continuous M. polymorpha forest stands on the island of Hawaii were differentiated into three genetic clusters, each of which grows in a distinctive environment and includes substantial genetic and phenotypic diversity. The three genetic clusters showed signatures of selection in genomic regions encompassing genes relevant to environmental adaptations, including genes associated with light utilization, oxidative stress, and leaf senescence, which are likely associated with the ecological differentiation of the species. Our demographic modeling suggested that the glaberrima cluster in wet environments maintained a relatively large population size and two clusters split: polymorpha in the subalpine zone and incana in dry and hot conditions. This ecological divergence possibly began before the species colonized the island of Hawaii. Interestingly, the three clusters recovered genetic connectivity coincidentally with a recent population bottleneck, in line with the weak reproductive isolation observed in the species. This study highlights that the degree of genetic differentiation between ecologically-diverged populations can vary depending on the strength of natural selection in the very early phases of speciation