Proton alleviation of growth inhibition by toxic metals (Al, La, Cu) in rhizobia

Free-living rhizobia are sensitive to soils and artificial media that are acidic. Both excessive H⁺ and Al released from acid-soluble minerals appear to be toxic. The complex, heterotrophic nutrient requirements of rhizobia and the joint occurrence of Al³⁺ and hydroxo-, sulphato-, phosphato-, fluoro-, and other Al species have prevented a precise attribution of toxicity to the Al species. In the present study, a medium composed of 0.3 mM MgSO₄, 2 mM CaCl₂, and 10 mM sucrose (the basal medium) enabled a 1000-fold cell increase at pH 4.6 or above. Additions of 1 μM AlCl₃ to the basal medium were highly intoxicating, especially at higher pH: below pH 5.0 cell numbers increased slightly; at pH 5.0 cell numbers did not change from the inoculum; at higher pH values the cell numbers declined. Similar trends were observed for La³⁺ and Cu²⁺ intoxication. Uptake of methylene blue, a positively charged dye useful as a probe of cell-surface electrical potential, was inhibited by pH reductions between pH 3.5 and 6.0. Factors that decrease cell-surface negativity (such as lower pH) reduce the intoxication by cations in plant roots, but the pH responsiveness of the rhizobia in our system was much greater than the pH responsiveness of plants. Although plant-root intoxication by mononuclear hydroxo-Al species has been discounted, rhizobia may be sensitive to those species. These results have implications for the management of rhizobia in acidic soils and for the development of resistant strains.     

Metal binding properties of high molecular weight soluble exudates from maize (Zea mays L.) roots

Summary A high molecular weight (MW > 1000) soluble root exudate fraction (HS) was isolated from hydroponic axenic maize cultures in order to investigate its metal-binding properties. Measurements of the maximum binding ability (MBA) and the overall stability constants (log K) for cadmium-, copper-, lead- and zinc-HS associations were obtained from dialysis and ion-selective electrode titrations. All results showed the occurrence of organometallic bindings. Data fitted to linear Langmuir isotherms. The MBA, measured by dialysis titration, varied from 160 to 206 mEq/100 g HS according to the nature of the metal. log K values, following the series Pb > Cu > Cd 5 Zn, varied from 3.15 to 3.65. Due to these metal-binding properties, soluble root products could play a role in the transfer of metal into the rhizosphere.     

Copper Tolerance and Accumulation of Elsholtzia splendens Nakai in a Pot Environment

ABSTRACT

Elsholtzia splendens Naki has been identified as a copper (Cu) geobotanical indicator. In this study, the effects of Cu supply levels (control, 100, 200, 400, 600, 800, 1000, 1200 mg kg¹) on the growth and Cu accumulation in E. splendens were studied in one pot experiment. The results showed that no reduction in shoot height and dry weight was noted when the plants were grown at Cu supply levels up to 1000 mg kg^?1 in soil. Slight stimulation on shoot growth was noted at Cu levels ≥ 100 mg kg^?1. Copper concentration in shoots and roots increased with increasing Cu levels, and reached a maximum of 1751 and 9.45 mg kg^?1 (DW) at 1200 mg Cu kg^?1. The amount of Cu accumulated in the roots and shoots were 313 and 22 μ g plant^?1 at external Cu levels of 1000 and 800 mg kg^?1, respectively. The shoot/root Cu ratios ranged from 0.005 to 0.008 and more than 92% of the total Cu taken up by E. splendens was accumulated in roots. Furthermore, Cu concentrations in roots and shoots were significant and positively correlated with total soil Cu, water, ammonium nitrate (NH₄NO₃), ammonium (NH₄)-acetate, and ethylenediaminetetraacetic acid (EDTA) extractable Cu. These results indicate that E. splendens can considered as a Cu tolerant and accumulated plant, and root is the major part for accumulation of Cu in E. splendens.     

Factors related to iron uptake by dicotyledonous and monocotyledonous plants. II. The reduction of Fe3+ as influenced by roots and inhibitors

In a companion paper (10), varieties of four plant species [two monocotyledons (oats and corn) and two dicotyledons (soybeans and tomato)] were shown to differ widely in their ability to respond to Fe‐stress. The ability of the more Fe‐efficient varieties was manifested by a lowering of the pH of the ambient medium of the root and/or by loss of reductants from the root. Both effects can enhance uptake of Fe by the roots, since Fe is taken up primarily, if not entirely, as Fe²⁺ ions. Thus, a given stressed plant has a means, under some degree of metabolic control, for modifying the root environment and, thereby, alleviating its chlorotic condition.

The present investigation deals with environmental factors, particularly chemical inhibitors, modifying the effectiveness of the stress response. Without inhibitors, excised root samples of the four species exhibited a wide range of abilities to reduce Fe³⁺ to Fe²⁺. Roots of the dicotyledonous species reduced about twice as much Fe³⁺ as did equal weights of the monocotyledonous species. Iron‐efficient tomato, soybean, and oat roots reduced more Fe³⁺ than did roots of the Fe‐inefficient varieties. The two corn varieties were about equal in their effectiveness.

Comparable samples of roots were also exposed to chemicals that induce or aggravate Fe chlorosis. Those found to be very effective inhibitors of Fe³⁺ reduction by the roots included: hydroxide, orthophosphate, pyrophosphate, Cu²⁺ and Ni²⁺. Other ions (includ ing Mn²⁺, Zn²⁺ and molybdate) and ethyl ammonium phosphate also inhibited Fe³⁺ reduction but to a lesser degree. Citrate, however, enhanced Fe³⁺ reduction. The degree of inhibition or enhancement differed for each of the varieties. In general, the Fe‐efficient plants were best able to reduce Fe³⁺ in spite of the inhibitory influence of the imposed treatments. Thus, our findings indicated that inhibition of the Fe³⁺ ‐reduction process at, or near, the periphery of the root is an apparent cause of Fe chlorosis.     

Transport patterns of foliar and root absorbed copper in bean seedlings

Abstract

Copper absorption by roots or leaf and transport to other parts were followed in 9‐days old bean (Phaseolus vulgaris L. cv. Vaghya) seedlings. Translocation was also measured in 4 cm segments of the stem. It was found that larger amount of Cu was retained in the roots and Cu was more mobile through phloem than through xylem, as indicated by the data on translocation from root and leaf. Bean plants were found to translocate more Cu to the stem than to other parts. Kinetic analysis of absorption by excised roots and stem segments revealed that the roots have a maximum uptake capacity and high affinity for Cu.     

Uptake and Translocation of Copper in Brassicaceae

Abstract

Ten cvs. of four Brassicaceae species were tested to evaluate their copper (Cu) uptake and translocation. Germination and root length tests indicated that Brassica juncea cv. Aurea and Raphanus sativus cvs. Rimbo and Saxa were the species with the highest germinability and longest roots at Cu concentrations ranging from 25 up to 200 µM. Raphanus sativus cv. Rimbo grown in hydroponic culture at increasing Cu concentrations (from 0.12 up to 40 µM) for 10 days produced a relatively high biomass (17.2 mg plant^?1) at the highest concentration and had a more efficient Cu translocation (17.8%) in comparison with cvs. Aurea and Saxa. The potential of cv. Rimbo for Cu uptake was then followed for 28 days at 5, 10, and 15 µM Cu. In comparison with the control, after 28 days of growth the 15 µM Cu‐treated plants showed a reduction in the tolerance index (?40%) and in the above‐ground dry biomass (?19%). On the contrary, an increase in the below‐ground dry weight was observed (+35%). Copper accumulated during the growth period both in the below‐ and above‐ground parts (about 14 and 4 µg plant^?1 at 10 and 15 µM Cu, respectively), but the translocation decreased from 50 to 30% in the last week at all the concentrations used. In addition, cv. Rimbo grown in a multiple element [cadmium (Cd), chromium (Cr), Cu, lead (Pb), and zinc (Zn)] naturally‐contaminated site accumulated all elements in the above‐ground part in a range from 5 to 62 µg plant^?1.     

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil 1

Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha^‐1.

Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha^‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha^‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha^‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Differences in mineral element concentrations for the four genotypes used were fairly extensive. The elements to show the greatest range among genotypes were Al and Si and the elements to show the least range among genotypes were P, K, and S. Care should be used in collecting leaf samples for plant analysis and genotypic differences for accumulation of mineral elements should be considered in interpretation of results.     

铜处理对大白菜芝麻状斑点病发生及总酚含量的影响

选择感病品系03B9 与抗病品系C24 为试材,在水培条件下,研究不同铜浓度处理对大白菜芝麻状斑点病发生、总
酚含量及多酚氧化酶活性的影响。结果表明：随着铜处理浓度的升高,两品系芝麻状斑点病的斑点数明显增加,03B9 芝麻
状斑点病发生程度明显高于C24。铜处理期间C24 总酚含量、PPO 活性较03B9 平均高出25.6% 和77.0%。试验结果初步表
明,水培条件下铜胁迫促进了大白菜芝麻状斑点病的发生,铜浓度与芝麻状斑点病发生程度有关,同时影响了叶柄总酚含量
及PPO 活性。     

铜离子对猕猴桃愈伤组织再分化培养的研究

以秦美猕猴桃茎段为外植体,诱导愈伤组织并进行猕猴桃再分化及生根试验。在分化培养基中分别添加不同浓度的铜离子进行筛选,以确定适于猕猴桃愈伤组织分化的最佳铜离子浓度。结果表明:再分化培养基中添加1.0 mg.L-1的铜离子时,可明显提高猕猴桃愈伤组织绿苗再分化率及生根率。但当铜离子浓度超过2.0 mg.L-1时,猕猴桃愈伤组织绿苗再分化率显著降低。     

Comparison of concentrations of copper in plasma and serum from farmed red deer (Cervus elaphus)

AIM: To determine the relationship between the concentrations of Cu in plasma and serum in red deer, and to compare this relationship with those previously reported in cattle and sheep.

METHODS: Paired serum and heparinised plasma samples from 114 red deer from 10 herds (n=6-20 per herd) were analysed for concentrations of Cu. Samples were collected either at slaughter (n=84; eight herds) or by jugular venepuncture (n=30; two herds). Thirty-nine of the samples taken at slaughter were from adult hinds from four herds, while other samples were taken from 10–14-month-old males, except for one herd (10 samples) where an equal number of 8–9-month-old males and females were sampled. The effect of age, gender and herd on the relationship between concentrations of Cu in plasma and serum was assessed using univariate ANOVA. The individual results for concentrations of Cu in serum were compared with those in plasma, using limits-of-agreement plotting.

RESULTS: The mean concentration of Cu in plasma was not significantly different from that of serum (0.048; 95% CI=-0.14 to 0.24 µmol/L). There was no effect of age, sex or herd on this relationship.

CONCLUSIONS: In deer, there was no significant difference between concentrations of Cu in plasma and serum regardless of age, sex or herd of origin.

CLINICAL RELEVANCE: In contrast to the situation in cattle and sheep, the concentration of Cu in serum can be used interchangeably with that in plasma for the estimation of concentration of Cu in blood of red deer.