Within Amaranthaceae, 33 different varieties, including local varieties from Japan, were grown in... more Within Amaranthaceae, 33 different varieties, including local varieties from Japan, were grown in 2012 in a field in the town of Iino in the Fukushima prefecture, which is located approximately 51 km north of Tokyo Electric Power Company, Fukushima Daiichi Nuclear Power Plant (FDNPP). The contamination level of the soil was 2770 ± 140 Bq kg −1 dry weight (134 Cesium (Cs) + 137 Cs, average ± SE), and the field was also cultivated in 2011. There was a significant varietal difference in the dry weight production, radiocesium accumulation and transfer factor (TF) of radiocesium from the soil to the plant. The ratio of the lowest TF to the highest TF was approximately 3. Because the ratio of 137 Cs to 133 Cs was significantly positive, radiocesium seems to be absorbed in a manner similar to that of 133 Cs. It is suggested that the varietal difference in the behavior of radiocesium uptake mainly depends on its genetic background rather than on environmental factors.
Soil contains various essential and nonessential elements, all of which can be absorbed by plants... more Soil contains various essential and nonessential elements, all of which can be absorbed by plants. Plant ionomics is the study of the accumulation of these elements (the ionome) in plants. The ionomic profile of a plant is affected by various factors, including species, variety, organ, and environment. In this study, we cultivated various vegetable crop species and cultivars under the same field conditions and analyzed the level of accumulation of each element in the edible and nonedible parts using ionomic techniques. The concentration of each element in the edible parts differed between species, which could be partly explained by differences in the types of edible organs (root, leaf, seed, and fruit). For example, the calcium concentration was lower in seeds and fruit than in other organs because of the higher dependency of calcium accumulation on xylem transfer. The concentration of several essential microelements and nonessential elements in the edible parts also varied greatly ...
Background Nitrogen (N), phosphorus (P), and potassium (K) are the three major fertilizer nutrien... more Background Nitrogen (N), phosphorus (P), and potassium (K) are the three major fertilizer nutrients, and adequate fertilization is one of the most important factors in plant production (Mengel and Kirkby 2001). Fertilization may affect the availability of elements other than those applied to soils. For example, the application of ammonium sulfate may increase the availability of some heavy metals in soils by lowering soil pH (Murányi et al. 1994). The effects of fertilization on soils are more obvious in a long-term fertilizer experiment
Molecular Microbial Ecology of the Rhizosphere, 2013
While phytic acid is a major form of organic phosphate in many soils, plant utilization of phytic... more While phytic acid is a major form of organic phosphate in many soils, plant utilization of phytic acid is normally limited; however, culture trials of Lotus japonicus using experimental field soil that had been managed without phosphate fertilizer for over 90 years showed significant usage of phytic acid applied to soil for growth and flowering and differences in the degree of growth, even in the same culture pot. To understand the key metabolic processes involved in soil phytic acid utilization, we analyzed rhizosphere soil microbial communities using molecular ecological approaches. Although molecular fingerprint analysis revealed changes in the rhizosphere soil microbial communities from bulk soil microbial community, no clear relationship between the microbiome composition and flowering status that might be related to phytic acid utilization of L. japonicus could be determined. However, metagenomic analysis revealed changes in the relative abundance of the classes Bacteroidetes, Betaproteobacteria, Chlorobi, Dehalococcoidetes and Methanobacteria, which include strains that potentially promote plant growth and phytic acid utilization, and some gene clusters relating to phytic acid utilization, such as alkaline phosphatase and citrate synthase, with the phytic acid utilization status of the plant. This study highlights phylogenetic and metabolic features of the microbial community of the L. japonicus rhizosphere and provides a basic understanding of how rhizosphere microbial communities affect the phytic acid status in soil.
Plant uptake water and nutrients from the surrounding environment of root. The area is called rhi... more Plant uptake water and nutrients from the surrounding environment of root. The area is called rhizosphere and we are especially interested in the role of those microorganisms who are playing an important role for the enhancing of plant growth. However, the functional diversity of the rhizosphere soil microorganisms is still unclear, because more than 99% of microbial species in soil are refractory to cultivation in laboratory growth conditions. Recently, the result of comparative analysis on environmental metagenomes was reported, and suggested that this approach can be an extremely valuable tool for the characterization of complex microbial communities. As the rhizosphere microbial community is intricately-intertwined with plant root and these community structure may be easily affected by plant root status, we have tried to improve the tools to analyze the rhizosphere soil sample by using comparative metagenomics approach, such as rhizosphere soil acquirement, soil DNA extraction, purification and amplification and plant DNA removal. By using these tools, we applied this approach to analyze the shift of rhizosphere microbial community structure with the plant root's status and distinguish the difference in the genes who may play important roles in the meaning of increasing the availability of nutrient to plant. The result of our study on the microbial communities of white lupin's rhizosphere soil showed that white lupin have a greater influence on their rhizosphere microbial communities than expected. Our study using Lotus japonicus suggested that previously unimaginable microbial gene clusters involved in phytic acid (which is a major soil organic phosphorus) utilization in the rhizosphere soil, though the overall meaning from the data cannot be simply assembled into metabolic change within these rhizospheres. We conclude that this approach on rhizosphere soil samples will likely provide a valuable method for the rizosphere microbial community analysis.
Wheat (Triticum aestivum L.) is one of the most important cereal crops of the world. Zinc deficie... more Wheat (Triticum aestivum L.) is one of the most important cereal crops of the world. Zinc deficiency is one of the most common deficiencies in soils worldwide. Several plant metabolic processes and biological functions are impaired under Zn deficient conditions. The most visible symptoms of zinc deficiency are a reduction in shoot growth, decrease in leaf size, chlorophyll degeneration and the emergence of whitish-brown necrotic patches on leaves. The genotypes that show the highest percent response to added Zn and are unable to grow well without Zn are defined as being susceptible to Zn deficiency and vice versa. Zinc efficiency is the ability of a plant to grow and produce grain when Zinc availability is low. Breeding cereals with enhanced zinc efficiency can decrease fertilizer dependency, improve seedling vigor, increase resistance to abiotic and biotic stress and enhance yield and nutritional value of wheat. A survey of the literature, as well as own experiences, show that there is enough genetic variation in wheat and alien species, particularly rye, for suitable zinc-efficient alleles. Genetic control is fairly simple, making breeding for this trait feasible. Since selection for Zinc efficiency in a breeding program is limited by the high spatial variability of zinc in field sites, better field screening techniques and selection criteria are needed to allow screening of early-generation segregating materials. Zn specific diagnostic methods like reflectance analysis and molecular markers (proteins /DNA markers) could complement the screening of wheat genotypes for zinc efficiency. Breeding wheat for enhanced zinc efficiency and higher grain yield would require concentrating the quantitative trait loci governing these traits in a few agronomic backgrounds through recombination breeding. This literature review paper delves into genetic variability, screening methods, plant breeding options and methodologies and other related issues for improving zinc efficiency in wheat.
The production of wheat is one of the most important breeding targets in India. The major constra... more The production of wheat is one of the most important breeding targets in India. The major constraints in the productivity are based on the limiting usage of water. In this mini-review, the focus is on the physiological traits of wheat plants to obtain the tolerance against heat and drought stress. This will encourage the breeding program on wheat in semi arid tropics like India.
In South Kalimantan, Indonesia, a large area of rice paddy field is suffered with acid sulfate so... more In South Kalimantan, Indonesia, a large area of rice paddy field is suffered with acid sulfate soil and the productivity of rice is supposed to be low. While in some paddy fields we have found that the yield of rice is larger than 5 ton ha −1 without any fertilizer. There assumed to be the contribution of nitrogen fixing bacteria for rice production by biological nitrogen fixation (BNF) under those low pH condition. We have screened bacteria from the rhizosphere and rhizoplane of local rice plant growing in natural field based on their growth on nitrogen free medium. We have obtained 26 isolates, and the majority of isolated bacteria belonged to the-proteobacteria (34.6 %) and others are-proteobacteria (19.2 %),-proteobacteria (0.38 %), Bacilli (19.2 %), and Actinobacteria (23.1 %) based on their 16S rDNA sequence. We have determined their nitrogenase activity and the existence of nifH gene by using PCR technique. Though all of the isolates can grow on nitrogen free medium, only five isolates belong to-proteobacteria have high nitrogenase activity. The existence of nifH gene was also confirmed in theses five isolates by using PCR technique. We presume that one of the mechanisms of the adaptation of these bacteria under acid sulfate soil is changing the surrounding pH. In bacterial culture medium, the change of pH during the incubation of these isolates was deeply regulated by the existence of several organic acid anions. In rice culture with soil experiments, under initial soil pH 3.5 condition, though rice growth was inhibited with the addition of 500 µM Al, inoculation with obtained isolate significantly alleviated Al stress. It is suggested that beneficial interactions of rice and free living nitrogen fixing bacteria might be operating to reducing root Al stress in acid sulfate soil.
The flow of labeled carbon in ectomycorrhizal and non-ectomycorrhizal seedlings of Japanese larch... more The flow of labeled carbon in ectomycorrhizal and non-ectomycorrhizal seedlings of Japanese larch (Larix kaempferi Sarg.) and its F1 hybrid (Larix gmelinii Rupr. × L. kaempferi) was studied. Larch seedlings were grown in a greenhouse for 110 days with larch forest soil (FM) or Suillus grevillei (SM) inoculum, or in the absence of ectomycorrhizal fungi (NM). Shoots of colonized and NM seedlings were exposed to a pulse of 14 CO 2 for 1 h under natural light. Seedlings were harvested following 0, 6 and 24 h of exposure to 14 CO 2. At the final harvest, SM seedlings of Japanese larch and hybrid larch allocated 2.6 and 2.5% more 14 C, respectively, to roots than NM seedlings. In contrast, FM seedlings of Japanese larch and hybrid larch allocated 6.5 and 18.0% more 14 C, respectively, to the stem than NM seedlings. Of the total 14 C detected in needle, stem and root fractions, FM and SM seedlings allocated a greater proportion than NM seedlings, perhaps because FM and SM seedlings had significantly (P < 0.05) higher photosynthetic rates than NM seedlings. As a result, FM and SM seedlings had greater dry masses than NM seedlings. Concentrations of nitrogen and phosphorus in FM and SM seedlings were significantly (P < 0.05) higher than in NM seedlings, as was stomatal conductance.
Effect of NH4-N and NO3-N on plant growth and tuber swelling of potato plant (Solanum tuberosum L... more Effect of NH4-N and NO3-N on plant growth and tuber swelling of potato plant (Solanum tuberosum L.) was examined, and the results obtained were as follows. 1) NH4-N stimulated tuber swelling, while N03-N stimulated the branching of stolons and stems, and shoot growth. 2) In plants grown with NHcN, a large amount of 15NH4-N was mainly partitioned into tubers and stems, whereas in plants grown with NOa-N, IsNO3-N was mainly partitioned into leaves, especially into the insoluble fraction. 3) Aspartic acid plus asparagine (Asx) in tubers predominated among amino acids and amides when the plants were grown with NH4-N. Also ~SNH4-N was incorporated into Asx in tubers, while, IsNO3-N was presumably transported to tubers in the form of Asx, which subsequently was actively metabolized into other amino acids in tubers. Thus, as the nitrogen form of NH4 + appeared to stimulate the Asx metabolism, Asx was transported to tubers, and mainly stored in tubers. On the other hand, the nitrogen form of NO3-was mainly transported into leaves, and NO3-N promoted vegetative growth.
, respiratory substances are used only for maintenance respiration when plants are exposed to the... more , respiratory substances are used only for maintenance respiration when plants are exposed to the dark conditions for a long period of time (more than 2 d). The maintenance respiration is also affected by the nitrogen status in plant, because protein turnover is one of the major energy consumption sources under maintenance process. Therefore, to determine whether respiratory substances are used only for maintenance, ~4C-[U]sucrose or a mixture of ~4C-[U]-amino acids was introduced to rice and soybean plants from the tip of leaf. Plants were grown under natural light conditions and under dark conditions for 4 d with 2 nitrogen levels (0.2 and 0.02 g N L-~ soil). After the introduction of the ~4C-compounds, the ~4C02 respiratory rate was monitored during 24 h, then the ~4C distribution to organic acids, free amino acids, proteins, sugars, and polysaccharides was analyzed. Following results were obtained. 1) When ~4C-[U]-sucrose or a mixture of ~4C-[U]-amino acids was introduced to the leaf of rice and soybean plants, the ~4C release rate by respiration was not affected by the nitrogen and light treatments except when ~4C-sucrose was introduced to soybean in the low N plot. The ~4C release rate from the ~4C-compounds introduced into leaf in the low N plot of soybean was higher in the dark treatment than in the natural light treatment. 2) ~4C-distribution ratio after introduction of ~4C-sucrose and a mixture of ~4C-amino acids to the leaf was not significantly affected by the nitrogen treatment. When ~4C-sucrose was introduced to rice leaf, the ~4C-distribution ratio to sugars and proteins was higher and that to polysaccharides was lower in the natural light treatment than in the dark treatment. The ~4C-distribution ratio was less affected by the light or nitrogen treatment in case of soybean leaf. 3) Although it was assumed that maintenance metabolism was dominant in the lower leaf (counted from the bottom), the 14C-distribution ratio was similar to that of upper leaf. 4) Nitrogen content of leaf was not different between rice and soybean in the high N treatment, unlike the ~4C-distribution ratio. In rice, the nitrogen content of leaf was about twice as high in the high N treatment compared with the low N treatment, while the ~4C-distribution ratio in leaf was stable regardless of nitrogen treatment. Based on the above results, it is suggested that since the ~4C-distribution ratio into each chemical component did not change regardless of light treat
Studies were carried out to identify the secreting portion of acid phosphatase (APase) in roots o... more Studies were carried out to identify the secreting portion of acid phosphatase (APase) in roots of lupin (Lupinus albus L.) and a key signal for the secretion from the roots. When lupin was grown in a nutrient solution without phosphate, the APase activity on the whole root surface increased and it was particularly high on the proteoid roots. When lupin was grown in a nutrient solution with 1.1 mM phosphate and transferred to a medium gel without phosphate, the activity of the secreted APase increased over the whole root system. Lupin was grown in a nutrient solution with 1.1 mM phosphate, the excised roots were transferred to a medium gel without phosphate, and the secreted APase activity was examined by activity staining of the medium gel after removal of the roots. The results indicated that the APase secretion from lupin roots was induced by a low phosphate concentration in the growth medium within 6 h. Even when the phosphate concentration in the lupin roots was sufficiently high, APase was secreted. It is concluded that a key signal for the APase secretion from lupin roots is not the low internal phosphate concentration, but the low phosphate concentration in the external solution.
This study evaluated the effects of exogenous LASAP2 for acid phosphatase (APase) and LASAP3 for ... more This study evaluated the effects of exogenous LASAP2 for acid phosphatase (APase) and LASAP3 for phytase of white lupin (Lupinus albus L.) on phosphorus (P) accumulation from organic P in soils. The potential for LASAP2-overexpressing tobacco (Nicotiana tabacum L.) to increase organic P in soil was examined in our previous study. However, LASAP2 has low specificity for phytate, the predominant form of unavailable P in the brown lowland soil. For the present study, we isolated the full length of LASAP3 cDNA and introduced it into tobacco plants using Agrobacterium-mediated transformation. Transgenic tobacco plants were grown in two different soils (Andosols and Regosols; high and low P-adsorption capacity, respectively) supplemented with either inorganic phosphate (þPi) or phytate (Po) as the sole P source, or control conditions that lacked phosphorus (No P). Dry matter production and P content of the transgenic line was higher than that of wild type in all treatments. The ratio of P accumulation increase by exogenous enzymes was found to be dependent on the P treatment and soil type. In all lines, the increase in þPo was less than that in þPi, but higher than in No P. The P uptake ability of plants in Regosols was higher than in Andosols for all treatments, suggesting that the P utilization efficiency of both Pi and Po is dependent on the solubility. In no soil type or P treatment was a significant difference found between LASAP2-and LASAP3-overexpressing lines. These results demonstrate that introducing an APase and phytase gene such as LASAP2 and LASAP3 into tobacco by genetic transformation is a promising strategy for improving P mobilization in soil, although the bottleneck for mobilization of phytate-P is not the specificity of the enzyme but its solubility in soils.
Growth inhibition caused by acid soils, especially due to P deficiency and Al stress, is a seriou... more 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. 464 detectable proteins spots were separated by 2D-PAGE. 56 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.
The Brachiaria hybrid cv. Mulato is well adapted to low-fertility acid soils deficient in phospho... more 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 14 C 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 Pdeficient 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.
Developmental changes of plant in the regulation of photosynthate distribution of leaves were stu... more Developmental changes of plant in the regulation of photosynthate distribution of leaves were studied in hydroponically cultivated rice by the 14 CO 2 tracer technique and analysis of the activity of the regulatory enzymes, sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), and pyruvate kinase (PK). The distribution of primary photosynthates into sugars, amino acids, organic acids, sugar phosphates, proteins, and polysaccharides was determined by column chromatography. The relative primary photosynthate distribution to the sugar phosphate fraction was significantly larger in the 5 th leaf than in the 6 th one. Correspondingly, the V max of PEPC was significantly higher in the 5 th than in the 6 th leaf, while no significant differences between leaves were detected in the other enzymes. As a consequence, the ratio of the V max of SPS and PEPC was lower in the 5 th than in the 6 th leaf. As the 5 th leaf develops before panicle initiation in rice, it predominantly supports vegetative growth, while the 6 th leaf develops after panicle initiation and thus contributes mainly to reproductive growth. We conclude that the physiological properties of each leaf are regulated developmentally. When the 6 th leaf became fully expanded (corresponding to the panicle initiation stage of plant), the distribution pattern of 14 C was transiently changed in the 5 th leaf, indicating that individual organs that are mainly involved in vegetative development are affected to some extent by the whole-plant-level physiological transformation that occurs at the transition from the vegetative to the reproductive stage.
mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), pho... more mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), pyruvate kinase, ribulose 1,5-bisphosphate carboxylase/oxygenase, glutamine synthetase 1, and glutamine synthetase 2 were investigated in leaves of rice plants grown at two nitrogen (N) supplies (N 0.5 , N 3.0). The relative gene expression patterns were similar in all leaves except for 9 th leaf, in which mRNA levels were generally depressed. Though increased N supply prolonged the expression period of each mRNA, it did not affect the relative expression intensity of any mRNA in a given leaf. SPS V max , SPS limiting and PEPC activities, and carbon flow were examined. The ratio between PEPC activity and SPS V max was higher in leaves developed at the vegetative growth stage (vegetative leaves: 5 th and 7 th leaves) than in leaves developed after the ear primordia formation stage (reproductive leaves: 9 th and flag leaves). PEPC activity and SPS V max decreased with declining leaf N content. After using 14 CO 2 the 14 C photosynthate distribution in the amino acid fraction was higher in vegetative than in reproductive leaves when compared for the same leaf N status. Thus, at high PEPC/SPS activities ratio, more 14 C photosynthate was distributed to the amino acid pool, whereas at higher SPS activity more 14 C was channelled into the saccharide fraction. Thus, leaf ontogeny was an important factor controlling photosynthate distribution to the Nor C-pool, respectively, regardless of the leaf N status.
A field experiment was conducted to investigate the carbon (C) and nitrogen (N) balance in relati... more A field experiment was conducted to investigate the carbon (C) and nitrogen (N) balance in relation to grain formation and leaf senescence in two different senescent types of maize (Zea mays L.), one stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55). In comparison with Hokkou 55, P3845 had a higher N concentration (N c) in the leaves and a higher specific N absorption rate by roots (SAR N), which indicated that a large amount of N was supplied to the leaves from the roots during maturation. This resulted in a higher photosynthetic rate, which supports saccharide distribution to roots. Thus, stay-green plants maintained a more balanced C and N metabolism between shoots and roots. Moreover, the coefficients of the relationship between the relative growth rate (RGR) and N c , and between the photon-saturated photosynthetic rate (P sat) and N c were lower in P3845. The P sat per unit N c in leaves was lower in the stay-green cultivars, which indicated that high yield was attained by longer green area duration and not by a high P sat per unit N c in the leaf. Consequently, a high P sat caused a high leaf senescence rate because C and N compounds will translocate actively from the leaves.
Within Amaranthaceae, 33 different varieties, including local varieties from Japan, were grown in... more Within Amaranthaceae, 33 different varieties, including local varieties from Japan, were grown in 2012 in a field in the town of Iino in the Fukushima prefecture, which is located approximately 51 km north of Tokyo Electric Power Company, Fukushima Daiichi Nuclear Power Plant (FDNPP). The contamination level of the soil was 2770 ± 140 Bq kg −1 dry weight (134 Cesium (Cs) + 137 Cs, average ± SE), and the field was also cultivated in 2011. There was a significant varietal difference in the dry weight production, radiocesium accumulation and transfer factor (TF) of radiocesium from the soil to the plant. The ratio of the lowest TF to the highest TF was approximately 3. Because the ratio of 137 Cs to 133 Cs was significantly positive, radiocesium seems to be absorbed in a manner similar to that of 133 Cs. It is suggested that the varietal difference in the behavior of radiocesium uptake mainly depends on its genetic background rather than on environmental factors.
Soil contains various essential and nonessential elements, all of which can be absorbed by plants... more Soil contains various essential and nonessential elements, all of which can be absorbed by plants. Plant ionomics is the study of the accumulation of these elements (the ionome) in plants. The ionomic profile of a plant is affected by various factors, including species, variety, organ, and environment. In this study, we cultivated various vegetable crop species and cultivars under the same field conditions and analyzed the level of accumulation of each element in the edible and nonedible parts using ionomic techniques. The concentration of each element in the edible parts differed between species, which could be partly explained by differences in the types of edible organs (root, leaf, seed, and fruit). For example, the calcium concentration was lower in seeds and fruit than in other organs because of the higher dependency of calcium accumulation on xylem transfer. The concentration of several essential microelements and nonessential elements in the edible parts also varied greatly ...
Background Nitrogen (N), phosphorus (P), and potassium (K) are the three major fertilizer nutrien... more Background Nitrogen (N), phosphorus (P), and potassium (K) are the three major fertilizer nutrients, and adequate fertilization is one of the most important factors in plant production (Mengel and Kirkby 2001). Fertilization may affect the availability of elements other than those applied to soils. For example, the application of ammonium sulfate may increase the availability of some heavy metals in soils by lowering soil pH (Murányi et al. 1994). The effects of fertilization on soils are more obvious in a long-term fertilizer experiment
Molecular Microbial Ecology of the Rhizosphere, 2013
While phytic acid is a major form of organic phosphate in many soils, plant utilization of phytic... more While phytic acid is a major form of organic phosphate in many soils, plant utilization of phytic acid is normally limited; however, culture trials of Lotus japonicus using experimental field soil that had been managed without phosphate fertilizer for over 90 years showed significant usage of phytic acid applied to soil for growth and flowering and differences in the degree of growth, even in the same culture pot. To understand the key metabolic processes involved in soil phytic acid utilization, we analyzed rhizosphere soil microbial communities using molecular ecological approaches. Although molecular fingerprint analysis revealed changes in the rhizosphere soil microbial communities from bulk soil microbial community, no clear relationship between the microbiome composition and flowering status that might be related to phytic acid utilization of L. japonicus could be determined. However, metagenomic analysis revealed changes in the relative abundance of the classes Bacteroidetes, Betaproteobacteria, Chlorobi, Dehalococcoidetes and Methanobacteria, which include strains that potentially promote plant growth and phytic acid utilization, and some gene clusters relating to phytic acid utilization, such as alkaline phosphatase and citrate synthase, with the phytic acid utilization status of the plant. This study highlights phylogenetic and metabolic features of the microbial community of the L. japonicus rhizosphere and provides a basic understanding of how rhizosphere microbial communities affect the phytic acid status in soil.
Plant uptake water and nutrients from the surrounding environment of root. The area is called rhi... more Plant uptake water and nutrients from the surrounding environment of root. The area is called rhizosphere and we are especially interested in the role of those microorganisms who are playing an important role for the enhancing of plant growth. However, the functional diversity of the rhizosphere soil microorganisms is still unclear, because more than 99% of microbial species in soil are refractory to cultivation in laboratory growth conditions. Recently, the result of comparative analysis on environmental metagenomes was reported, and suggested that this approach can be an extremely valuable tool for the characterization of complex microbial communities. As the rhizosphere microbial community is intricately-intertwined with plant root and these community structure may be easily affected by plant root status, we have tried to improve the tools to analyze the rhizosphere soil sample by using comparative metagenomics approach, such as rhizosphere soil acquirement, soil DNA extraction, purification and amplification and plant DNA removal. By using these tools, we applied this approach to analyze the shift of rhizosphere microbial community structure with the plant root's status and distinguish the difference in the genes who may play important roles in the meaning of increasing the availability of nutrient to plant. The result of our study on the microbial communities of white lupin's rhizosphere soil showed that white lupin have a greater influence on their rhizosphere microbial communities than expected. Our study using Lotus japonicus suggested that previously unimaginable microbial gene clusters involved in phytic acid (which is a major soil organic phosphorus) utilization in the rhizosphere soil, though the overall meaning from the data cannot be simply assembled into metabolic change within these rhizospheres. We conclude that this approach on rhizosphere soil samples will likely provide a valuable method for the rizosphere microbial community analysis.
Wheat (Triticum aestivum L.) is one of the most important cereal crops of the world. Zinc deficie... more Wheat (Triticum aestivum L.) is one of the most important cereal crops of the world. Zinc deficiency is one of the most common deficiencies in soils worldwide. Several plant metabolic processes and biological functions are impaired under Zn deficient conditions. The most visible symptoms of zinc deficiency are a reduction in shoot growth, decrease in leaf size, chlorophyll degeneration and the emergence of whitish-brown necrotic patches on leaves. The genotypes that show the highest percent response to added Zn and are unable to grow well without Zn are defined as being susceptible to Zn deficiency and vice versa. Zinc efficiency is the ability of a plant to grow and produce grain when Zinc availability is low. Breeding cereals with enhanced zinc efficiency can decrease fertilizer dependency, improve seedling vigor, increase resistance to abiotic and biotic stress and enhance yield and nutritional value of wheat. A survey of the literature, as well as own experiences, show that there is enough genetic variation in wheat and alien species, particularly rye, for suitable zinc-efficient alleles. Genetic control is fairly simple, making breeding for this trait feasible. Since selection for Zinc efficiency in a breeding program is limited by the high spatial variability of zinc in field sites, better field screening techniques and selection criteria are needed to allow screening of early-generation segregating materials. Zn specific diagnostic methods like reflectance analysis and molecular markers (proteins /DNA markers) could complement the screening of wheat genotypes for zinc efficiency. Breeding wheat for enhanced zinc efficiency and higher grain yield would require concentrating the quantitative trait loci governing these traits in a few agronomic backgrounds through recombination breeding. This literature review paper delves into genetic variability, screening methods, plant breeding options and methodologies and other related issues for improving zinc efficiency in wheat.
The production of wheat is one of the most important breeding targets in India. The major constra... more The production of wheat is one of the most important breeding targets in India. The major constraints in the productivity are based on the limiting usage of water. In this mini-review, the focus is on the physiological traits of wheat plants to obtain the tolerance against heat and drought stress. This will encourage the breeding program on wheat in semi arid tropics like India.
In South Kalimantan, Indonesia, a large area of rice paddy field is suffered with acid sulfate so... more In South Kalimantan, Indonesia, a large area of rice paddy field is suffered with acid sulfate soil and the productivity of rice is supposed to be low. While in some paddy fields we have found that the yield of rice is larger than 5 ton ha −1 without any fertilizer. There assumed to be the contribution of nitrogen fixing bacteria for rice production by biological nitrogen fixation (BNF) under those low pH condition. We have screened bacteria from the rhizosphere and rhizoplane of local rice plant growing in natural field based on their growth on nitrogen free medium. We have obtained 26 isolates, and the majority of isolated bacteria belonged to the-proteobacteria (34.6 %) and others are-proteobacteria (19.2 %),-proteobacteria (0.38 %), Bacilli (19.2 %), and Actinobacteria (23.1 %) based on their 16S rDNA sequence. We have determined their nitrogenase activity and the existence of nifH gene by using PCR technique. Though all of the isolates can grow on nitrogen free medium, only five isolates belong to-proteobacteria have high nitrogenase activity. The existence of nifH gene was also confirmed in theses five isolates by using PCR technique. We presume that one of the mechanisms of the adaptation of these bacteria under acid sulfate soil is changing the surrounding pH. In bacterial culture medium, the change of pH during the incubation of these isolates was deeply regulated by the existence of several organic acid anions. In rice culture with soil experiments, under initial soil pH 3.5 condition, though rice growth was inhibited with the addition of 500 µM Al, inoculation with obtained isolate significantly alleviated Al stress. It is suggested that beneficial interactions of rice and free living nitrogen fixing bacteria might be operating to reducing root Al stress in acid sulfate soil.
The flow of labeled carbon in ectomycorrhizal and non-ectomycorrhizal seedlings of Japanese larch... more The flow of labeled carbon in ectomycorrhizal and non-ectomycorrhizal seedlings of Japanese larch (Larix kaempferi Sarg.) and its F1 hybrid (Larix gmelinii Rupr. × L. kaempferi) was studied. Larch seedlings were grown in a greenhouse for 110 days with larch forest soil (FM) or Suillus grevillei (SM) inoculum, or in the absence of ectomycorrhizal fungi (NM). Shoots of colonized and NM seedlings were exposed to a pulse of 14 CO 2 for 1 h under natural light. Seedlings were harvested following 0, 6 and 24 h of exposure to 14 CO 2. At the final harvest, SM seedlings of Japanese larch and hybrid larch allocated 2.6 and 2.5% more 14 C, respectively, to roots than NM seedlings. In contrast, FM seedlings of Japanese larch and hybrid larch allocated 6.5 and 18.0% more 14 C, respectively, to the stem than NM seedlings. Of the total 14 C detected in needle, stem and root fractions, FM and SM seedlings allocated a greater proportion than NM seedlings, perhaps because FM and SM seedlings had significantly (P < 0.05) higher photosynthetic rates than NM seedlings. As a result, FM and SM seedlings had greater dry masses than NM seedlings. Concentrations of nitrogen and phosphorus in FM and SM seedlings were significantly (P < 0.05) higher than in NM seedlings, as was stomatal conductance.
Effect of NH4-N and NO3-N on plant growth and tuber swelling of potato plant (Solanum tuberosum L... more Effect of NH4-N and NO3-N on plant growth and tuber swelling of potato plant (Solanum tuberosum L.) was examined, and the results obtained were as follows. 1) NH4-N stimulated tuber swelling, while N03-N stimulated the branching of stolons and stems, and shoot growth. 2) In plants grown with NHcN, a large amount of 15NH4-N was mainly partitioned into tubers and stems, whereas in plants grown with NOa-N, IsNO3-N was mainly partitioned into leaves, especially into the insoluble fraction. 3) Aspartic acid plus asparagine (Asx) in tubers predominated among amino acids and amides when the plants were grown with NH4-N. Also ~SNH4-N was incorporated into Asx in tubers, while, IsNO3-N was presumably transported to tubers in the form of Asx, which subsequently was actively metabolized into other amino acids in tubers. Thus, as the nitrogen form of NH4 + appeared to stimulate the Asx metabolism, Asx was transported to tubers, and mainly stored in tubers. On the other hand, the nitrogen form of NO3-was mainly transported into leaves, and NO3-N promoted vegetative growth.
, respiratory substances are used only for maintenance respiration when plants are exposed to the... more , respiratory substances are used only for maintenance respiration when plants are exposed to the dark conditions for a long period of time (more than 2 d). The maintenance respiration is also affected by the nitrogen status in plant, because protein turnover is one of the major energy consumption sources under maintenance process. Therefore, to determine whether respiratory substances are used only for maintenance, ~4C-[U]sucrose or a mixture of ~4C-[U]-amino acids was introduced to rice and soybean plants from the tip of leaf. Plants were grown under natural light conditions and under dark conditions for 4 d with 2 nitrogen levels (0.2 and 0.02 g N L-~ soil). After the introduction of the ~4C-compounds, the ~4C02 respiratory rate was monitored during 24 h, then the ~4C distribution to organic acids, free amino acids, proteins, sugars, and polysaccharides was analyzed. Following results were obtained. 1) When ~4C-[U]-sucrose or a mixture of ~4C-[U]-amino acids was introduced to the leaf of rice and soybean plants, the ~4C release rate by respiration was not affected by the nitrogen and light treatments except when ~4C-sucrose was introduced to soybean in the low N plot. The ~4C release rate from the ~4C-compounds introduced into leaf in the low N plot of soybean was higher in the dark treatment than in the natural light treatment. 2) ~4C-distribution ratio after introduction of ~4C-sucrose and a mixture of ~4C-amino acids to the leaf was not significantly affected by the nitrogen treatment. When ~4C-sucrose was introduced to rice leaf, the ~4C-distribution ratio to sugars and proteins was higher and that to polysaccharides was lower in the natural light treatment than in the dark treatment. The ~4C-distribution ratio was less affected by the light or nitrogen treatment in case of soybean leaf. 3) Although it was assumed that maintenance metabolism was dominant in the lower leaf (counted from the bottom), the 14C-distribution ratio was similar to that of upper leaf. 4) Nitrogen content of leaf was not different between rice and soybean in the high N treatment, unlike the ~4C-distribution ratio. In rice, the nitrogen content of leaf was about twice as high in the high N treatment compared with the low N treatment, while the ~4C-distribution ratio in leaf was stable regardless of nitrogen treatment. Based on the above results, it is suggested that since the ~4C-distribution ratio into each chemical component did not change regardless of light treat
Studies were carried out to identify the secreting portion of acid phosphatase (APase) in roots o... more Studies were carried out to identify the secreting portion of acid phosphatase (APase) in roots of lupin (Lupinus albus L.) and a key signal for the secretion from the roots. When lupin was grown in a nutrient solution without phosphate, the APase activity on the whole root surface increased and it was particularly high on the proteoid roots. When lupin was grown in a nutrient solution with 1.1 mM phosphate and transferred to a medium gel without phosphate, the activity of the secreted APase increased over the whole root system. Lupin was grown in a nutrient solution with 1.1 mM phosphate, the excised roots were transferred to a medium gel without phosphate, and the secreted APase activity was examined by activity staining of the medium gel after removal of the roots. The results indicated that the APase secretion from lupin roots was induced by a low phosphate concentration in the growth medium within 6 h. Even when the phosphate concentration in the lupin roots was sufficiently high, APase was secreted. It is concluded that a key signal for the APase secretion from lupin roots is not the low internal phosphate concentration, but the low phosphate concentration in the external solution.
This study evaluated the effects of exogenous LASAP2 for acid phosphatase (APase) and LASAP3 for ... more This study evaluated the effects of exogenous LASAP2 for acid phosphatase (APase) and LASAP3 for phytase of white lupin (Lupinus albus L.) on phosphorus (P) accumulation from organic P in soils. The potential for LASAP2-overexpressing tobacco (Nicotiana tabacum L.) to increase organic P in soil was examined in our previous study. However, LASAP2 has low specificity for phytate, the predominant form of unavailable P in the brown lowland soil. For the present study, we isolated the full length of LASAP3 cDNA and introduced it into tobacco plants using Agrobacterium-mediated transformation. Transgenic tobacco plants were grown in two different soils (Andosols and Regosols; high and low P-adsorption capacity, respectively) supplemented with either inorganic phosphate (þPi) or phytate (Po) as the sole P source, or control conditions that lacked phosphorus (No P). Dry matter production and P content of the transgenic line was higher than that of wild type in all treatments. The ratio of P accumulation increase by exogenous enzymes was found to be dependent on the P treatment and soil type. In all lines, the increase in þPo was less than that in þPi, but higher than in No P. The P uptake ability of plants in Regosols was higher than in Andosols for all treatments, suggesting that the P utilization efficiency of both Pi and Po is dependent on the solubility. In no soil type or P treatment was a significant difference found between LASAP2-and LASAP3-overexpressing lines. These results demonstrate that introducing an APase and phytase gene such as LASAP2 and LASAP3 into tobacco by genetic transformation is a promising strategy for improving P mobilization in soil, although the bottleneck for mobilization of phytate-P is not the specificity of the enzyme but its solubility in soils.
Growth inhibition caused by acid soils, especially due to P deficiency and Al stress, is a seriou... more 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. 464 detectable proteins spots were separated by 2D-PAGE. 56 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.
The Brachiaria hybrid cv. Mulato is well adapted to low-fertility acid soils deficient in phospho... more 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 14 C 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 Pdeficient 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.
Developmental changes of plant in the regulation of photosynthate distribution of leaves were stu... more Developmental changes of plant in the regulation of photosynthate distribution of leaves were studied in hydroponically cultivated rice by the 14 CO 2 tracer technique and analysis of the activity of the regulatory enzymes, sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), and pyruvate kinase (PK). The distribution of primary photosynthates into sugars, amino acids, organic acids, sugar phosphates, proteins, and polysaccharides was determined by column chromatography. The relative primary photosynthate distribution to the sugar phosphate fraction was significantly larger in the 5 th leaf than in the 6 th one. Correspondingly, the V max of PEPC was significantly higher in the 5 th than in the 6 th leaf, while no significant differences between leaves were detected in the other enzymes. As a consequence, the ratio of the V max of SPS and PEPC was lower in the 5 th than in the 6 th leaf. As the 5 th leaf develops before panicle initiation in rice, it predominantly supports vegetative growth, while the 6 th leaf develops after panicle initiation and thus contributes mainly to reproductive growth. We conclude that the physiological properties of each leaf are regulated developmentally. When the 6 th leaf became fully expanded (corresponding to the panicle initiation stage of plant), the distribution pattern of 14 C was transiently changed in the 5 th leaf, indicating that individual organs that are mainly involved in vegetative development are affected to some extent by the whole-plant-level physiological transformation that occurs at the transition from the vegetative to the reproductive stage.
mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), pho... more mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), pyruvate kinase, ribulose 1,5-bisphosphate carboxylase/oxygenase, glutamine synthetase 1, and glutamine synthetase 2 were investigated in leaves of rice plants grown at two nitrogen (N) supplies (N 0.5 , N 3.0). The relative gene expression patterns were similar in all leaves except for 9 th leaf, in which mRNA levels were generally depressed. Though increased N supply prolonged the expression period of each mRNA, it did not affect the relative expression intensity of any mRNA in a given leaf. SPS V max , SPS limiting and PEPC activities, and carbon flow were examined. The ratio between PEPC activity and SPS V max was higher in leaves developed at the vegetative growth stage (vegetative leaves: 5 th and 7 th leaves) than in leaves developed after the ear primordia formation stage (reproductive leaves: 9 th and flag leaves). PEPC activity and SPS V max decreased with declining leaf N content. After using 14 CO 2 the 14 C photosynthate distribution in the amino acid fraction was higher in vegetative than in reproductive leaves when compared for the same leaf N status. Thus, at high PEPC/SPS activities ratio, more 14 C photosynthate was distributed to the amino acid pool, whereas at higher SPS activity more 14 C was channelled into the saccharide fraction. Thus, leaf ontogeny was an important factor controlling photosynthate distribution to the Nor C-pool, respectively, regardless of the leaf N status.
A field experiment was conducted to investigate the carbon (C) and nitrogen (N) balance in relati... more A field experiment was conducted to investigate the carbon (C) and nitrogen (N) balance in relation to grain formation and leaf senescence in two different senescent types of maize (Zea mays L.), one stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55). In comparison with Hokkou 55, P3845 had a higher N concentration (N c) in the leaves and a higher specific N absorption rate by roots (SAR N), which indicated that a large amount of N was supplied to the leaves from the roots during maturation. This resulted in a higher photosynthetic rate, which supports saccharide distribution to roots. Thus, stay-green plants maintained a more balanced C and N metabolism between shoots and roots. Moreover, the coefficients of the relationship between the relative growth rate (RGR) and N c , and between the photon-saturated photosynthetic rate (P sat) and N c were lower in P3845. The P sat per unit N c in leaves was lower in the stay-green cultivars, which indicated that high yield was attained by longer green area duration and not by a high P sat per unit N c in the leaf. Consequently, a high P sat caused a high leaf senescence rate because C and N compounds will translocate actively from the leaves.
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