Effect of bicarbonate and root zone temperature on uptake of Zn,Fe, Mn and Cu by different rice cultivars (Oryza sativa L.) grown in calcareous soil

Pot experiments were conducted with a calcareous soil (Inceptisol) to elucidate the effects of bicarbonate (0 and 20 mM) and root zone temperature (15° and 25°C) on the uptake of Zn, Fe, Mn and Cu by "Zn-efficient" and "Zn-inefficient" rice cultivars. Bicarbonate decreased concentrations and total uptake of Zn in shoots of "Zn-inefficient" cultivars, especially of IR 26 at 25°C, but not in Zn-efficient cultivars. Bicarbonate decreased concentrations and uptake of Fe in shoots of Zn inefficient cultivars, particularly in IR 26. Concentrations and total uptake of Mn were lower in bicarbonate treatment in the Zn-inefficient cultivars at 15°C, and in all cultivars at 25°C. However, concentration and uptake of Cu were not affected by bicarbonate in all cultivars. Compared to the 25°C root zone temperature, the concentrations and total uptake of both Zn and Cu in shoots at 15°C were lower in Zn-inefficient than in the Zn-efficient cultivars. The results indicate that Zn-efficiency in rice is causally related to high tolerance of plant to elavated bicarbonate concentrations in soil solution.     

Metal-humic complexes and plant micronutrient uptake: a study based on different plant species cultivated in diverse soil types

There are several studies in the literature dealing with the effect of metal-humic complexes on plant metal uptake, but none of them correlate the physicochemical properties of the complexes with agronomic results. Our study covers both aspects under various experimental conditions. A humic extract (SHE) obtained from a sapric peat was selected for preparing the metal–humic complexes used in plant experiments. Fe–, Zn– and Cu–humic complexes with a reaction stoichiometry of 2:0.25 (humic:metal, w/w) were chosen after studying their stability and solubility with respect to pH (6–9) and the humic:metal reaction stoichiometry. Wheat and alfalfa plants were greenhouse cultured in pots containing one of three model soils: an acid, sandy soil and two alkaline, calcareous soils. Treatments were: control (no additions), SHE (53 mg kg^–1 of SHE), and metal (Cu, Zn and Fe)–SHE complexes (2.5 and 5 mg kg^–1 of metal rate and a SHE concentration to make 53 mg kg ^–1). Cu- and Zn–humic complexes significantly (p0.05) increased the plant uptake and the DTPA-extractable soil fraction of complexed micronutrients in most plant–soil systems. However, these effects were associated with significant increases (p0.05) of shoot and root dry weight only in alfalfa plants. In wheat, significant increases of root and shoot dry matter were only observed in the Cu–humic treated plants growing in the acid soil, where Cu deficiency was more intense. The Fe–humic complex did not increase Fe plant assimilation in any plant–soil system, but SHE increased Fe-uptake and/or DTPA-extractable soil Fe in the wheat–calcareous soil systems. These results, taken together with those obtained from the study of the pH- and SHE:metal ratio-dependent SHE complex solubility and stability, highlight the importance of the humic:Fe complex stoichiometry on iron bioavailability as a result of its influence on complex solubility.     

Genetic diversity for grain nutrients in wild emmer wheat: potential for wheat improvement

Background and Aims

Micronutrient malnutrition, particularly zinc and iron deficiency, afflicts over three billion people worldwide due to low dietary intake. In the current study, wild emmer wheat (Triticum turgidum ssp. dicoccoides), the progenitor of domesticated wheat, was tested for (1) genetic diversity in grain nutrient concentrations, (2) associations among grain nutrients and their relationships with plant productivity, and (3) the association of grain nutrients with the eco-geographical origin of wild emmer accessions.

Methods

A total of 154 genotypes, including wild emmer accessions from across the Near Eastern Fertile Crescent and diverse wheat cultivars, were characterized in this 2-year field study for grain protein, micronutrient (zinc, iron, copper and manganese) and macronutrient (calcium, magnesium, potassium, phosphorus and sulphur) concentrations.

Key Results

Wide genetic diversity was found among the wild emmer accessions for all grain nutrients. The concentrations of grain zinc, iron and protein in wild accessions were about two-fold greater than in the domesticated genotypes. Concentrations of these compounds were positively correlated with one another, with no clear association with plant productivity, suggesting that all three nutrients can be improved concurrently with no yield penalty. A subset of 12 populations revealed significant genetic variation between and within populations for all minerals. Association between soil characteristics at the site of collection and grain nutrient concentrations showed negative associations between soil clay content and grain protein and between soil-extractable zinc and grain zinc, the latter suggesting that the greatest potential for grain nutrient minerals lies in populations from micronutrient-deficient soils.

Conclusions

Wild emmer wheat germplasm offers unique opportunities to exploit favourable alleles for grain nutrient properties that were excluded from the domesticated wheat gene pool.     

Mechanisms of waterlogging tolerance in wheat – a review of root and shoot physiology

We review the detrimental effects of waterlogging on physiology, growth and yield of wheat. We highlight traits contributing to waterlogging tolerance and genetic diversity in wheat. Death of seminal roots and restriction of adventitious root length due to O₂ deficiency result in low root:shoot ratio. Genotypes differ in seminal root anoxia tolerance, but mechanisms remain to be established; ethanol production rates do not explain anoxia tolerance. Root tip survival is short‐term, and thereafter, seminal root re‐growth upon re‐aeration is limited. Genotypes differ in adventitious root numbers and in aerenchyma formation within these roots, resulting in varying waterlogging tolerances. Root extension is restricted by capacity for internal O₂ movement to the apex. Sub‐optimal O₂ restricts root N uptake and translocation to the shoots, with N deficiency causing reduced shoot growth and grain yield. Although photosynthesis declines, sugars typically accumulate in shoots of waterlogged plants. Mn or Fe toxicity might occur in shoots of wheat on strongly acidic soils, but probably not more widely. Future breeding for waterlogging tolerance should focus on root internal aeration and better N‐use efficiency; exploiting the genetic diversity in wheat for these and other traits should enable improvement of waterlogging tolerance.     

MTP1-dependent Zn sequestration into shoot vacuoles suggests dual roles in Zn tolerance and accumulation in Zn-hyperaccumulating plants

The integral membrane protein Thlaspi goesingense metal tolerance protein 1 (TgMTP1) has been suggested to play an important role in Zn hyperaccumulation in T. goesingense . Here, we show that the TgMTP1 protein is accumulated to high levels at the vacuolar membrane in shoot tissue of T. goesingense . TgMTP1 is likely to act in the transport of Zn into the vacuole, enhancing both Zn accumulation and tolerance. By specifically expressing TgMTP1 in Arabidopsis thaliana shoots, we show that TgMTP1, localized at the vacuolar membrane, can drive the enhanced shoot accumulation of Zn by initiating a systemic Zn deficiency response. The systematic response includes increased expression of Zn transporters ( ZIP3 , ZIP4 , ZIP5 and ZIP9 ) in both shoot and root tissue. Furthermore, shoot-specific accumulation of TgMTP1 at the vacuolar membrane also leads to increased resistance to Zn in A. thaliana , probably through enhanced Zn compartmentalization in the vacuole. Such evidence leads to the conclusion that the high levels of TgMTP1 at the vacuolar membrane in shoot tissue of the Zn hyperaccumulator T. goesingense play a role in both Zn tolerance and enhanced Zn uptake and accumulation, via the activation of a systemic Zn deficiency response.     

Boron efficiency in oilseed rape: I. Genotypic variation demonstrated in field and pot grown Brassica napus L. and Brassica juncea L.

Boron (B) efficiency of oilseed rape (Brassica napus) and mustard (B. juncea) genotypes was determined on a low B soil at Mt. Compass, South Australia. B efficiency was observed in oilseed rape genotypes, Zhongyou 821, Dunkeld and Zheyou 2, and in mustard genotypes Pusa Bold and CSIRO 6. Genotypes grown in the field were also grown under glass-house conditions, in pots filled with pre-washed sand extracted from the Mt. Compass field site. Two B treatments, one B adequate (0.25 mg B kg⁻¹ soil) and one B deficient (imposed by omission) were used to indicate whether vegetative response to B could predict final yield response and provide a more convenient selection criterion for identifying B-efficient germplasm. Vegetative response of 35 d old (D35) genotypes grown in pot culture closely reflected field response, indicating the expression of B efficiency traits in early growth, and its potential use in selection. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of suboptimal root zone temperatures and shoot demand on net translocation of micronutrients from the roots to the shoot of maize

The effects of suboptimal root zone temperatures (RZTs) on net translocation rates from the roots to the shoots and the concentrations of Fe, Mn, Zn, and Cu were examined in maize grown in nutrient solution or soil. Plants were grown at 12 °C, 18 °C and 24 °C RZT. At each RZT, the growth-related shoot demand for nutrients was varied by independently modifying the temperature of the shoot base (SBT) including the apical shoot meristem. The net translocation rates of Mn and Zn from the roots to the shoots were reduced at low RZTs, irrespective of the SBT and of the substrate (soil or nutrient solution). Obviously, the net translocation rates of Mn and Zn at low RZT were mainly regulated by temperature effects on the roots and not by the chemical nutrient availability in the rhizosphere or by shoot growth rate as controlled by SBTs. When both RZT and SBT were reduced, the decrease in net translocation rates of Mn and Zn was similar to the decline in the shoot growth rate and concentrations of Mn and Zn in the shoot fresh matter were not greatly affected or were even increased by low RZT. However, at high SBT and low RZT in nutrient solution, the depressed net translocation rates of Mn and Zn combined with the increased shoot growth resulted in significantly decreased concentrations of Mn and Zn in the shoot, indicating that Mn and Zn may become deficient even at high chemical availability. By contrast to Mn and Zn, the net translocation rates of Fe and Cu at all RZTs were markedly enhanced by increased SBTs. Accordingly, the concentrations of Fe and Cu in the shoot fresh matter were not greatly affected by RZTs, irrespective of the SBTs. These results indicate that the ability of roots to supply Fe and Cu to the shoot was internally regulated by the growth related shoot demand per unit of roots. Deceased 21 September 1996 Deceased 21 September 1996     

SELENIUM: AN ESSENTIAL ELEMENT FOR GROWTH OF THE COASTAL MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1,2

An obligate requirement for selenium is demonstrated in axenic culture of the coastal marine diatom Thalassiosira pseudonana (clone 3H) (Hust.) Hasle and Heimdal grown in artificial seawater medium. Selenium deficiency was characterized by a reduction in growth rate and eventually by a cessation of cell division. The addition of 10⁻¹⁰ M Na₂eO₃ to nutrient enriched artifical seawater resulted in excellent growth of T. pseudonana and only a slight inhibition of growth occurred at Na₂SeO₃ concentrations of 10⁻³ and 10_-2 M. By contrast, Na₂SeO₄ failed to support growth of T. pseudonana when supplied at concentrations less than 10⁻⁷ M and the growth rate at this concentration was only one quarter of the maximum growth rate. The addition of 10⁻³ and 10⁻² M Na₂SeO₄ to the culture medium was toxic and cell growth was completely inhibited. Eleven trace elements were tested for their ability to replace the selenium requirement by this alga and all were without effect. In selenium-deficient and selenium-starved cultures of T. pseudonana cell volume increased as much as 10-fold as a result of an increase in cell length (along the pervalvar axis) but cell width was constant. It is concluded that selenium is an indispensable element for the growth of T. pseudonana and it should be included as a nutrient enrichment to artificial seawater medium when culturing this alga.     

微量元素对籼稻愈伤组织分化成苗的影响

通过研究MS培养基中碘、硼、锰、锌、钼、铜、钴以及铁8种微量无素对愈伤组织分化成苗的影响,结果表明:缺少碘、硼、锰、锌、钼、钴的培养基对籼稻愈伤组织分化成苗影响不大,而缺少铜和铁的培养基对籼稻愈伤组织分化成苗影响很大,添加不同浓度铁和铜元素的试验表明,在铁盐浓度为0.10mmo1.L-1,铜浓度为1.5×10-4mmo1.L-1时,分化成苗效果较好,而铁盐浓度分别在0.05mmol.L-1、0.15mmol.L-1、0.20mmol.L-1、0.40mmol.L-1,铜浓度分别在0.5×10-4mmol.L-1、1.0×10-4mmol.L-1、2.0×10-4mmol.L-1、4.0×10-4mmol.L-1时,对籼稻分化成苗和生长均不利。