著者
Wasaki, J., Sakaguchi, J., Yamamura, T., Ito, S., Shinano, T., Osaki, M., Kandeler, E

雑誌
Soil Science and Plant Nutrition, 64(6), 686-696. 2018

概要
We studied microbe-plant interactions of white lupin, a cluster root-forming plant, under low P and N conditions to examine increased nutrient acquisition by plants either by a shift to a more specialized microbial community or changes in microbial enzyme production. White lupin plants were grown in rhizoboxes filled with either P- or N-deficient soil; fertilized soil was used as control. After cultivation of plants in a glasshouse for 41 d, plant growth (shoot and roots) and P and N accumulation in shoots were measured. Microbial functions were analyzed by P- and N-cycling enzymes. The microbial community structure was estimated by fingerprinting (denaturing gradient gel electrophoresis) and sequencing techniques. P deficiency induced the released citrate and acid phosphomonoesterases from cluster roots and stimulated the production of microbe-derived alkaline phosphomonoesterase in the rhizosphere. P deficiency decreased microbial diversity in the cluster root rhizosphere. Increased relative abundance of Burkholderiales in the rhizosphere of P deficient plants might be responsible for the degradation of different organic P fractions such as phytates. N deficiency induced an increase of the number of nodules and P concentration in shoot as well as roots of white lupin. We clarified that high release of citrate from cluster roots might be the preferred mechanisms to meet the P demand of nodulated plants under N deficiency. In addition, the high abundance of Rhizobiales and Rhodospirillales in the rhizosphere of cluster roots showed that the importance of N-fixing microorganisms under N deficiency. The contribution of rhizosphere microorganisms due to similar activities of N-cycling enzymes under the two different N treatments is less important for N nutrition of plants. Further understanding of the regulation of cluster roots under N-deficiency will provide new information on the interactions between P and N nutrition.
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著者
Wu, L., Kobayashi, Y., Wasaki, J., Koyama, H.

雑誌
Soil Science and Plant Nutrition, 64(6), 697-704. 2018

概要
The beneficial effects of organic acids (OAs) excretion from plant roots were first proposed as being associated with the mechanism of superior phosphorus utilization by the cluster roots of white lupin (Lupinus albus L.), and these effects are now widely accepted as pleiotropic effects associated with stress tolerance of plants. Excreted OAs detoxify rhizotoxic aluminum, recruit beneficial bacterium for induced systemic resistance, and modify root architecture to enhance phosphorus starvation. OA excretion is probably optimized in the carbon economy and is coordinately regulated with other traits that additively confer each stress factor. Here we present an overview of the molecular physiology of OA excretion from roots, how plants activate OA excretion, and how this excretion can be managed as a specific response.
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著者
Maruyama, H., Sasaki, T., Yamamoto, Y., Wasaki, J.

雑誌
Plant and Cell Physiology, 60(1), 107-115. 2019

概要
Under phosphorus (P)-deficient conditions, organic acid secretion from roots plays an important role in P mobilization from insoluble P in the soil. In this study, we characterized AtALMT3, a homolog of the Arabidopsis thaliana aluminum-activated malate transporter family gene. Among the 14 AtALMT family genes, only AtALMT3 was significantly up-regulated in P-deficient roots. AtALMT3 promoter::β-glucuronidase is expressed in the epidermis in roots, especially in root hair cells. AtALMT3 protein was localized in the plasma membrane and in small vesicles. Fluorescence of AtALMT3::GFP was not observed on the vacuole membrane of protoplast after lysis, indicating that AtALMT3 localizes mainly in the plasma membrane. Compared with the wild-type (WT) line, malate exudation in the AtALMT3-knockdown line (atalmt3-1) and overexpression line (atalmt3-2) under P deficiency were, respectively, 37% and 126%. In contrast, no significant difference was found in citrate exudation among these lines. The complementation of the atalmt3-1 line with AtALMT3 recovered the malate exudation to the level of the WT. Taken together, these results suggest that AtALMT3 localized in root hair membranes is involved in malate efflux in response to P deficiency.
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著者
Imai, K., Sugihara, S., Wasaki, J., Tanaka, H.

雑誌
Agronomy, 9(2), 68. 2019

概要
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 (P_i) and organic P (P_o) 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 P_i 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.
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