Hitoshi Obata

Effects of cadmium on mineral nutrient concentrations in plants differing in tolerance for cadmium

Abstract The effects of 3 d treatments with 0.3 and 1.0 mg‐L‐1 of cadmium (Cd) on selected mineral nutrient composition in plants differing in tolerance for Cd were studied. The concentrations of potassium (K) decreased in Cd‐sensitive kidney bean and pea and that of manganese (Mn) decreased in the semi‐resistant rice and maize plants with increasing application of Cd in the culture solution. Copper (Cu) content increased in the roots of the plants above, but no changes in Cu contents were observed in the Cd resistant cucumber and pumpkin plants. Calcium (Ca), magnesium (Mg), and zinc (Zn) did not show any clear tendency with Cd applications in any of the plants examined. Water absorption by kidney bean was reduced by Cd, but that of rice and cucumber was not. Permeability of the plasma membrane of root cells may be affected by Cd, whereas absorption of some of the elements and water may be prevented.

Transgenic tobacco plants expressing a rice cysteine synthase gene are tolerant to toxic levels of cadmium

Summary Plants tolerate heavy metals through sequestration with cysteine-rich peptides, phytochelatins. In this reaction, the rate limiting step is considered to be the supply of cysteine, which is synthesized by cysteine synthase (CS, EC 4.2.99.8) from hydrogen sulfide and O -acetylserine. In this study, we transformed tobacco ( Nicotiana tabacum ) plants with RCS1, a cytosolic cysteine synthase gene of rice ( Oryza sativa ), and examined their sensitivity to cadmium. The transgenic plants had up to 3-fold higher activity of cysteine synthase than wild-type plants. Upon exposure to cadmium, they exhibited obvious tolerance with much greater growth than wild-type plants. The level of phytochelatins in shoots was higher in transgenic than in wild-type plants after cadmium treatment, suggesting that cadmium was actively trapped by phytochelatins. However, the cadmium concentration per g fresh weight of whole transgenic plants was 20 percnt; lower than that of wild-type plants, suggesting cadmium to be either actively excreted or diluted by fast growth. Genetic analysis of progenies clearly showed segregation of cadmium tolerance, indicating that the trait resulted from the introduced gene. These results suggest that introduction of a cysteine synthase gene into tobacco plants resulted not only in high level production of sulfur-containing compounds that detoxify cadmium, but also in active elimination of cadmium toxicity from plant bodies.

Characterization of Mycorrhizas Formed by Glomus sp. on Roots of Hypernodulating Mutants of Lotus japonicus

Lotusjaponicus hypernodulating mutants, Ljsym78-1 and Ljsym78-2, by the arbuscular mycorrhizal fungus Glomus sp. was characterized. The mutants are defective in systemic autoregulation of nodulation and nitrate inhibition, and form an excess of nodules and lateral roots. The percent root length colonized by the arbuscular mycorrhizal fungi was significantly higher for the mutant than wild-type roots. Detailed assessment of the colonization indicated that the percentage of colonization by arbuscules was increased, but that by external hyphae, internal hyphae and vesicles was decreased, in the mutant roots compared with the wild-type. The succinate dehydrogenase activity of arbuscules, external hyphae and internal hyphae showed similar trends. In addition, the majority of individual arbuscules that formed on the mutant roots had a well-developed and seemingly tough morphology. The results suggest that mutation at the Ljsym78 locus positively stimulates the growth and activity of arbuscules, but leads to reduced growth and activity of hyphae. We report the first identification of Lotus japonicus mutants that show significantly increased arbuscule formation and termed these mutants Arb++.

Effects of Zinc Deficiency on the Nitrogen Metabolism of Meristematic Tissues of Rice Plants with Reference to Protein Synthesis

Zinc deficiency remarkably depressed the zinc concentrations in the meristematic tissues of rice plants. When the zinc concentration was decreased to a level of less than 100 ppm, disorders of the nitrogen metabolism appeared. Zinc deficiency severely depressed the production of proteins in meristematic tissues and brought about the accumulation of free amino acids and ami des (above all, asparagine, glutamine, and alanine). Two-dimensional separation patterns of proteins obtained by O’Parrell’s technique suggested that the composition of the proteins remained almost unchanged although their amount was remarkably reduced.

Involvement of histidine-rich domain of ZIP family transporter TjZNT1 in metal ion specificity

The Zrt/Irt-like protein (ZIP) family generally contributes to metal homeostasis by regulating cation transport into the cytoplasm. Most ZIP members have a long variable loop between transmembrane domains III and IV, and these loops are predicted to be located in the cytoplasm. The loops contain a histidine-rich domain (HRD) postulated to serve as a metal ion binding site; however, its role has not yet been determined. We previously determined that deletion of the HRD did not affect the Ni tolerance ability of TjZNT1-a ZIP transporter that confers high Ni tolerance to yeast. In this study, we investigated the effect of HRD deletion on the ion transport ability of TjZNT1. The deletion of HRD increased the specificity for Zn2+, but not for Cd2+. In addition, we confirmed subcellular localizations of TjZNT1 and HRD-deleted mutants by green fluorescence protein (GFP)-fused proteins, indicating that the deletion of HRD did not affect the localization of TjZNT1. From these results, we propose that the HRD could be involved in the ion specificity of TjZNT1.

Methane formation and substrate utilisation in anaerobic rice soils as affected by fertilisation

Anaerobic incubation of air-dried rice soils was carried out to investigate the effects of long-term fertiliser application on CH4 formation and the utilisation of glucose and acetate. The soil samples were taken after the crop harvest in 1995 from the long-term experimental plots which had been fertilised with chemical fertiliser alone (CF), or chemical fertiliser in combination with rice straw compost (RC), cow manure (CM) or rice straw (RS) for 20 y. The soil from the CM plot showed the highest rate of CH4 formation, especially when supplemented with glucose or acetate. The RS plot soil showed significant CH4 formation only when glucose was added. CH4 formation in the CF and RC plots was low, even glucose or acetate was added. The pool sizes of acetate ranged from 360 nmol g−1 in the CF plot to 818 nmol g−1 in the RS plot. The rate of acetate metabolism was lowest in the CF plot (26.6 nmol g−1 h−1) and highest in the CM plot (47.6 nmol g−1 h−1), respectively. The results using [1-14C] and [2-14C]acetate and 14C-bicarbonate indicated that demethylation of acetate was the main pathway (>80%) of CH4 formation. CH4 formation from [1-14C]acetate or bicarbonate was less than 15% in all plots. Thus, the long-term application of different fertilisers did not change the pathway of methanogenesis. However, the portion of [2-14C]acetate converted to CH4 was different between plots; about 50% in the CF and RC plots and >90% and nearly 80% in the CM and RS plots. It was found that the efficiency of acetate utilisation and the metabolic rate of acetate were the important factors in determining the magnitude of methanogenesis from acetate in these soils. Addition of BES did not accumulate acetate, suggesting the presence of other acetate-utilising bacteria in these soils.

Distribution of Ni and Zn in the leaves of Thlaspi japonicum growing on ultramafic soil

Abstract A Ni-hyperaccumulator, Thlaspi japonicum, grown on ultramafic soil contained large amounts of Ni and Zn in its shoot. The Ni content of the leaves was the highest (3,424 mg kg−1) in the lower epidermis, which had many stomata, followed by the leaf edge, upper epidermis, which had few stomata, and mesophyll. By contrast, the Zn content was the highest (615 mg kg−1) in the upper epidermis followed by the lower epidermis, and was the lowest at the leaf edge. Using a microscope, the dimethylglyoxime-stained Ni-compound was observed as rod-shaped crystals mainly around the stomata and the projections of the leaf edge. In addition, a considerable amount of Ni was excreted via the guttation fluid (0.67 to 1.33 mg L−1), while the concentration of Zn in the guttation fluid was very low (0.01–0.10 mg L−1). In mature leaves, the Ni content was almost constant during the growth period, while the Zn content decreased once around the summer solstice, reached the highest level in midsummer, and decreased thereafter. In young leaves, however, the Ni and Zn contents increased to a level similar to that in mature leaves in midsummer, and decreased after early September. These data suggest that Ni is translocated along with the transpiration stream and concentrated around stomata, and that the excess amount of Ni is excreted via the guttation fluid. This mechanism may not operate for Zn accumulation in this plant. Zn in mature leaves may be supplied to young leaves on demand for rapid growth.

Effect of Zinc Deficiency on 80S Ribosome Content of Meristematic Tissues of Rice Plant

1. A convenient method was developed for the determination of 80S ribosome content using an analytical ultracentrifuge. 2. Zinc deficiency depressed the content of free 80S ribosomes in the meristematic tissues of rice plant, followed by reduced protein contents.

Effects of zinc deficiency on the growth, proteins, and other constituents of yeast, Saccharomyces cerevisiae, cells

Abstract To carry out a series of experiments in order to analyze the effects of Zn deficiency on protein synthesis in higher plants, we used a budding yeast, Saccharomyces cerevisiae, as model organism. Yeast cells were cultured in a chemically defined Burkholder minimum medium with and without Zn. When the Zn concentration in the cells decreased to a level of less than 100 mg kg-1 dry weight, cell growth was depressed. The cells in the —Zn culture swelled, and after further culture, they formed clusters. Zinc deficiency enhanced the Ca concentration in the cells and did not affect the K and Mg concentrations. Zinc deficiency remarkably depressed the protein content of the cells. Some soluble proteins and peptides disappeared and some proteins and peptides appeared in the —Zn culture. pI of one protein shifted from 8.0 to 7.8 in the —Zn culture under nondenaturing conditions, and the N-terminal amino acid sequence of this protein showed a 100% homology with enolase (EC 4.2.1.11).

Age-Dependent Manganese Hyperaccumulation in Chengiopanax sciadophylloides (Araliaceae)

ABSTRACT Chengiopanax sciadophylloides is a Japanese tree previously known to accumulate large concentrations of manganese (Mn) in its leaves. To date, this distinctive characteristic has not been fully clarified to use these characteristics for physiological models for research of mineral acquisition and phytoremediation of Mn. In this investigation, the accumulation of Mn in both small young and tall mature C. sciadophylloides trees, and its overall distribution through young trees were examined. The foliar Mn concentrations of mature trees were consistently found to exceed 10,000 mg kg− 1 DW, with recorded maximum values of up to 23,500 mg kg− 1, while those of young trees were found to be around 8,700 mg kg− 1. The concentrations of eleven other metals in C. sciadophylloides was also measured, and found that concentration of each divalent cation was lower than average values of many samples from wide area in Japan.