Reports of studies supported by Grant-in-Aid for Research from the Graduate School of Biosphere Science, Hiroshima University

基盤研究サポート Grant-in-Aid for Fundamental Research ・環境ウイルスのキャラクタリゼーションに関する基礎研究…中井敏博 ・ウシの行動反応と気質関連遺伝子多型との関係…豊後貴嗣 ・クラスター構造の根を形成する植物の低リン適応特性の解明…和崎

Evaluation of Cellulolytic and Hemicellulolytic Abilities of Fungi Isolated from Coffee Residue and Sawdust Composts

This study focused on the evaluation of cellulolytic and hemicellulolytic fungi isolated from sawdust compost (SDC) and coffee residue compost (CRC). To identify fungal isolates, the ITS region of fungal rRNA was amplified and sequenced. To evaluate enzyme production, isolates were inoculated onto wheat bran agar plates, and enzymes were extracted and tested for cellulase, xylanase, β-glucanase, mannanase, and protease activities using different azurine cross-linked (AZCL) substrates. In total, 18 isolates from SDC and 29 isolates from CRC were identified and evaluated. Four genera (Aspergillus, Galactomyces, Mucor, and Penicillium) and five genera (Aspergillus, Coniochaeta, Fusarium, Penicillium, and Trichoderma/Hypocrea) were dominant in SDC and CRC, respectively. Penicillium sp., Trichoderma sp., and Aspergillus sp. displayed high cellulolytic and hemicellulolytic activities, while Mucor isolates exhibited the highest β-glucanase and mannanase activities. The enzyme analyses revealed that Penicillium, Aspergillus, and Mucor isolates significantly contributed to the degradation of SDC, whereas Penicillium, Aspergillus, and Trichoderma isolates had a dominant role in the degradation of CRC. Notably, isolates SDCF5 (P. crustosum), CRCF6 (P. verruculosum), and CRCF2 and CRCF16 (T. harzianum/H. lixii) displayed high activity regarding cellulose and hemicellulose degradation, which indicates that these species could be beneficial for the improvement of biodegradation processes involving lignocellulosic materials

Metabolic alterations proposed by proteome in rice roots grown under low P and high Al concentration under low pH

Growth inhibition caused by acid soils, especially due to P deficiency and Al stress, is a serious problem for crop production. To comprehend the adaptation mechanisms of rice plants to P deficiency and Al stress conditions, a proteomic analysis of rice roots in hydroponic cultivation was demonstrated. Four hundred and sixty-four detectable proteins spots were separated by 2D-PAGE. Fifty-six of 94 spots selected at random were identified by peptide mass fingerprinting. In general, the proteomic alterations under P deficiency and Al stress conditions were similar trend, indicating that a common metabolic system is responsive to both P deficiency and Al stress. An increase in nucleotide monomer synthesis was indicated from the related proteomic alterations, which mediate the reversible reactions of the triose phosphate/pentose phosphate pool, and the oxidative reactions of the pentose phosphate pathway under both stress conditions. Carbon flow to the TCA cycle and N assimilation were altered in proteomic level. The changes could be contributed to the complementation of TCA components from suppression of photosynthates partitioning from leaves, and partly contribute to organic acid secretion. Induction of S-adenosylmethionine (SAM) synthetase is a significant and unique response to Al stress, suggesting that SAM is related to ethylene-mediated inhibition of root growth and/or the alteration of cell wall structures and polymers in roots

Influence of arsenic stress on synthesis and localization of low-molecular-weight thiols in Pteris vittata

The roles of low-molecular-weight thiols (LMWTs), such as glutathione and phytochelatins, in arsenic (As) tolerance and hyperaccumulation in Pteris vittata an As-hyperaccumulator fern remain to be better understood. This study aimed to thoroughly characterize LMWT synthesis in P. vittata to understand the roles played by LMWTs in As tolerance and hyperaccumulation. LMWT synthesis in P. vittata was induced directly by As, and not by As-mediated oxidative stress. Expression of PvECS2. one of the putative genes of γ-glutamylcysteine synthetase (γECS), increases in P. vittata shoots at 48 h after the onset of As exposure, almost corresponding to the increase in the concentrations of γ-glutamylcysteine and glutathione. Furthermore, localization of As showed similar trends to those of LMWTs in fronds at both whole-frond and cellular levels. This study thus indicates the specific contribution of LMWTs to As tolerance in P. vittata. γECS may be responsible for the As-induced enhancement of LMWT synthesis

Possible solubilization of various mineral elements in the rhizosphere of Lupinus albus L

Lupinus albus L. (lupin) has a high tolerance for phosphorus deficient conditions as its roots can solubilize the unavailable phosphorus in the rhizosphere soil. The roots may also be able to solubilize other elements, but this requires further investigation. In this study, therefore, we conducted two experiments to comprehensively investigate the effects of lupin roots on the mineral dynamics of the rhizosphere soil. First, a mixed cropping experiment was conducted, in which lupin shared a rhizosphere with soybean (Glycine max (L.) Merr.) in a long-term experimental field with four fertilizer treatments: complete fertilization (+NPK), without nitrogen (-N), without phosphorus (-P), and without potassium (-K). The results of shoot dry weight of plants cultivated alone indicated that lupin is highly tolerant to all N, P, and K deficiencies, while soybean can adapt to N deficiency with the help of rhizobia but is less tolerant to P and K deficiencies than lupin. When mixed-cropped with lupin, the concentrations of many elements in the soybean leaf increased, particularly with the -N and -P treatments. Furthermore, soybean growth was significantly improved when cropped with lupin in the -N and -P treatments. Second, a comparison of the elemental profiles of hydroponically and field-soil-grown plants was conducted. Under hydroponic conditions, the rhizosphere effect is negligible when the culture medium is well circulated. The lupin/soybean ratios for leaf mineral concentrations were considerably larger in the field cultivated plants when compared with the hydroponic cultivations for elements such as sodium, potassium, cesium, phosphorus, iron, copper, and molybdenum, as there were lower concentrations of these elements in the soybean leaves in the field. These results indicate that lupin roots can solubilize a variety of insoluble elements in the soil, which may be the reason why lupin can adapt to various nutrient deficient soils. In the lupin rhizosphere, the solubilization of cesium, which is generally strongly fixed by soil minerals and not easily leached, was particularly pronounced. This implies that the surface structure of clay minerals might be altered in the lupin rhizosphere, resulting in the fixed forms of various elements becoming available

Low Phosphorus Tolerance Mechanisms: Phosphorus Recycling and Photosynthate Partitioning in the Tropical Forage Grass, Brachiaria Hybrid cultivar Mulato Compared with Rice

The Brachiaria hybrid cv. Mulato is well adapted to low-fertility acid soils deficient in phosphorus (P). To study the grassy forage’s mechanisms for tolerating low P supply, we compared it with rice (Oryza sativa L. cv. Kitaake). We tested by using nutrient solution cultures, and quantified the effects of P deficiency on the enzymatic activities of phosphohydrolases and on carbon metabolism in P-deficient leaves. While P deficiency markedly induced activity of phosphohydrolases in both crops, the ratio of inorganic phosphorus to total P in leaves was greater in Brachiaria hybrid. Phosphorus deficiency in leaves also markedly influenced the partitioning of carbon in both crops. In the Brachiaria hybrid, compared with rice, the smaller proportion of 14C partitioned into sugars and the larger proportion into amino acids and organic acids in leaves coincided with decreased levels of sucrose and starch. Hence, in P-deficient leaves of the Brachiaria hybrid, triose-P was metabolized into amino acids or organic acids. Results thus indicate that the Brachiaria hybrid, compared with rice, tolerates low P supply to leaves by enhancing sugar catabolism and by inducing the activity of several phosphohydrolases. This apparently causes rapid P turnover and enables the Brachiaria hybrid to use P more efficiently.This is a pre-copy editing, author-produced PDF of an article accepted for publication in "Plant and Cell Physiology" following peer review. The definitive publisher-authenticated version is available online

広島県庄原市猫山における蛇紋岩植物の現状

広島県庄原市に所在する猫山は，広島県内では珍しい蛇紋岩地である。同山山頂周辺の露岩地を含む草地には，蛇紋岩地特有の植物が生育していることから，学術的に重要な場所として調査が行われてきた。しかしながら，近年における報告が少なく，その現状が分かっていない。そこで本研究では，猫山の山頂周辺において，2021 年から2022 年にかけて，生育する植物種の調査を行った。調査の結果，蛇紋岩地に特徴的なネコヤマヒゴタイSaussurea modesta Kitam. やイブキジャコウソウThymus quinquecostatus Celak. var. ibukiensis (Kudô) H.Hara などの絶滅危惧種を含む，過去に記録のある植物の大部分を確認した。しかし，蛇紋岩地特有の植物の生育範囲は草地や岩場などに極めて限定されており，今後の遷移の進行や気候変動，人為的攪乱などの影響を考慮すると，長期的な保全対策が必要と考えられる。Mt. Nekoyama, located in Shobara City, is one of the rare serpentine areas in Hiroshima Prefecture. Plants unique to serpentine soils grow in the grasslands and rocky areas around the summit. For this reason, researchers have conducted floral surveys here for years. However, there have only been a few reports in recent years, and the flora’s current status is unknown. Thus, we surveyed the serpentine flora on Mt. Nekoyama from 2021 to 2022. The presence of most of the plants recorded in the past was confirmed. These included endangered plants characteristic of serpentinite areas, such as Saussurea modesta Kitam. and Thymus quinquecostatus Celak. var. ibukiensis (Kudô) H. Hara. However, the range of serpentinite plants was particularly limited to grasslands and rocky areas. Long-term conservation measures are necessary considering the effects of succession, climate change, and human disturbance.本研究の一部は，令和3 年度および令和4 年度に，公益社団法人日本植物園協会が環境省から受託した希少野生植物の生息域外保全検討実施委託業務の一環として行った

Effects of White Lupin and Groundnut on Fractionated Rhizosphere Soil P of Different P-Limited Soil Types in Japan

Phosphorus (P) is an essential nutrient for crop production, while most soil P is the less labile P associated with Aluminum (Al) and Iron (Fe) in acidic soils of Japan. The objectives of this study were to evaluate the effects of two contrasting P-efficient legumes (white lupin, WL (Lupinus albus L.); and groundnut, GN (Arachis hypogaea L.)) on rhizosphere soil P dynamics in different soil types of Japan, such as Al-rich volcanic-soil, Fe-rich red-yellow-soil, and sandy-soil, with or without historical fertilization managements (3 soil types × 2 managements = 6 soil samples). We conducted a 56-day pot experiment, and analyzed the plant P uptake and fractionated P of rhizosphere and bulk soils, based on the Hedley-fractionation method. We observed that GN P uptake was generally larger than that in WL in most soil types and managements. WL significantly decreased the labile P in most soils and also decreased the less labile inorganic P (Pi) and organic P (Po) in fertilized Red-yellow-soil, which has much crystalline Fe, though GN did not. In contrast, both WL and GN significantly decreased the less labile Pi in fertilized volcanic-soil, which has much non-crystalline Al. These results indicate that (1) characteristics of less labile P uptake by P efficient legumes were different between the soil types and managements, and (2) WL efficiently solubilized the less labile P than GN in fertilized red-yellow soil, while GN efficiently absorbed the larger amount of P than WL, especially in volcanic- and sandy-soil