Determination of acute oral toxicity of flumethrin in honey bees.

Flumethrin is one of many pesticides used for the control and treatment of varroatosis in honey bees and for the control of mosquitoes and ticks in the environment. For the control of varroatosis, flumethrin is applied to hives formulated as a plastic strip for several weeks. During this time, honey bees are treated topically with flumethrin, and hive products may accumulate the pesticide. Honey bees may indirectly ingest flumethrin through hygienic behaviors during the application period and receive low doses of flumethrin through comb wax remodeling after the application period. The goal of our study was to determine the acute oral toxicity of flumethrin and observe the acute effects on motor coordination in honey bees (Apis mellifera anatoliaca). Six doses (between 0.125 and 4.000 microg per bee) in a geometric series were studied. The acute oral LD50 of flumethrin was determined to be 0.527 and 0.178 microg per bee (n = 210, 95% CI) for 24 and 48 h, respectively. Orally administered flumethrin is highly toxic to honey bees. Oral flumethrin disrupted the motor coordination of honey bees. Honey bees that ingested flumethrin exhibited convulsions in the antennae, legs, and wings at low doses. At higher doses, partial and total paralysis in the antennae, legs, wings, proboscises, bodies, and twitches in the antennae and legs were observed.

Biofortification and localization of zinc in wheat grain.

Zinc (Zn) deficiency associated with low dietary intake is a well-documented public health problem, resulting in serious health and socioeconomic problems. Field experiments were conducted with wheat to test the role of both soil and foliar application of ZnSO4 in Zn concentration of whole grain and grain fractions (e.g., bran, embryo and endosperm) in 3 locations. Foliar application of ZnSO4 was realized at different growth stages (e.g., stem elongation, boot, milk, dough stages) to study the effect of timing of foliar Zn application on grain Zn concentration. The rate of foliar Zn application at each growth stage was 4 kg of ZnSO4·7H2O ha(-1). Laser ablation (LA)-ICP-MS was used to follow the localization of Zn within grain. Soil Zn application at a rate of 50 kg of ZnSO4·7H2O ha(-1) was effective in increasing grain Zn concentration in the Zn-deficient location, but not in the locations without soil Zn deficiency. In all locations, foliar application of Zn significantly increased Zn concentration in whole grain and in each grain fraction, particularly in the case of high soil N fertilization. In Zn-deficient location, grain Zn concentration increased from 11 mg kg(-1) to 22 mg kg(-1) with foliar Zn application and to 27 mg kg(-1) with a combined application of ZnSO4 to soil and foliar. In locations without soil Zn deficiency, combination of high N application with two times foliar Zn application (e.g., at the booting and milk stages) increased grain Zn concentration, on average, from 28 mg kg(-1) to 58 mg kg(-1). Both ICP-OES and LA-ICP-MS data showed that the increase in Zn concentration of whole grain and grain fractions was pronounced when Zn was sprayed at the late growth stage (e.g., milk and dough). LA-ICP-MS data also indicated that Zn was transported into endosperm through the crease phloem. To our knowledge, this is the first study to show that the timing of foliar Zn application is of great importance in increasing grain Zn in wheat, especially in the endosperm part that is the predominant grain fraction consumed in many countries. Providing a large pool of Zn in vegetative tissues during the grain filling (e.g., via foliar Zn spray) is an important practice to increase grain Zn and contribute to human nutrition.

Peanut/maize intercropping induced changes in rhizosphere and nutrient concentrations in shoots.

A greenhouse study was conducted to investigate the rhizosphere effects on iron (Fe), phosphorus (P), nitrogen (N), potassium (K), calcium (Ca), zinc (Zn), and manganese (Mn) nutrition in peanut plants (Arachis hypogaea L.) by intercropping them with maize (Zea mays L.). In addition, we studied the release of phytosiderophores and the ferric reductase activity of roots, pH and acid phosphatases in the rhizosphere and bulk soil, and the secretion of acid phosphatases in roots. Our results revealed that shoot yields of peanut and maize plants were decreased by intercropping the plants, as compared to monocultured plants. Growing peanut plants in a mixture with maize, enhanced the shoot concentrations of Fe and Zn nearly 2.5-fold in peanut, while the Mn concentrations of peanut were little affected by intercropping. In the case of maize, the shoot concentrations of Fe, Zn and Mn were not significantly affected by intercropping with peanut. Intercropping also improved the shoot K concentration of peanut and maize, while it negatively affected the Ca concentration. In the intercropping of peanut/maize, the acid phosphatase activity of the rhizosphere and bulk soil and root secreted acid phosphatases were significantly higher than that of monocultured peanut and maize. In accordance, the shoot P concentrations of peanut and maize plants were much higher when they were intercropped with peanut or maize, respectively. The rhizosphere and bulk soil pH values were not clearly affected by different cropping systems. When compared to their monoculture treatments, the secretion of phytosiderophore from roots and the root ferric reducing capacity of the roots were either not affected or increased by 2-fold by the intercropping, respectively. The results indicate the importance of intercropping systems as a promising management practice to alleviate Fe deficiency stress. Intercropping also contributes to better nutrition of plants with Zn, P and K, most probably by affecting biological and chemical process in the rhizosphere.

Phytosiderophore release in Aegilops tauschii and Triticum species under zinc and iron deficiencies.

Using three diploid (Triticum monococcum, AA), three tetraploid (Triticum turgidum, BBAA), two hexaploid (Triticum aestivum and Triticum compactum, BBAADD) wheats and two Aegilops tauschii (DD) genotypes, experiments were carried out under controlled environmental conditions in nutrient solution (i) to study the relationships between the rates of phytosiderophore (PS) release from the roots and the tolerance of diploid, tetraploid, and hexaploid wheats and AE: tauschii to zinc (Zn) and iron (Fe) deficiencies, and (ii) to assess the role of different genomes in PS release from roots under different regimes of Zn and Fe supply. Phytosiderophores released from roots were determined both by measurement of Cu mobilized from a Cu-loaded resin and identification by using HPLC analysis. Compared to tetraploid wheats, diploid and hexaploid wheats were less affected by Zn deficiency as judged from the severity of leaf symptoms. Aegilops tauschii showed very slight Zn deficiency symptoms possibly due to its slower growth rate. Under Fe-deficient conditions, all wheat genotypes used were similarly chlorotic; however, development of chlorosis was first observed in tetraploid wheats. Correlation between PS release rate determined by Cu-mobilization test and HPLC analysis was highly significant. According to HPLC analysis, all genotypes of Triticum and AE: tauschii species released only one PS, 2'-deoxymugineic acid, both under Fe and Zn deficiency. Under Zn deficiency, rates of PS release in tetraploid wheats averaged 1 micromol x (30 plants)(-1) x (3 h)(-1), while in hexaploid wheats rate of PS release was around 14 micromol x (30 plants)(-1) x (3 h)(-1). Diploid wheats and AE: tauschii accessions behaved similarly in their capacity to release PS and intermediate between tetraploid and hexaploid wheats regarding the PS release capacity. All Triticum and Aegilops species released more PS under Fe than Zn deficiency, particularly when the rate of PS release was expressed per unit dry weight of roots. On average, the rates of PS release under Fe deficiency were 3.0, 5.7, 8.4, and 16 micromol x (30 plants)(-1) x (3 h)(-1) for AE: tauschii, diploid, tetraploid and hexaploid wheats, respectively. The results of the present study show that the PS release mechanism in wheat is expressed effectively when three genomes, A, B and D, come together, indicating complementary action of the corresponding genes from A, B and D genomes to activate biosynthesis and release of PS.

Uptake and retranslocation of leaf-applied cadmium (109Cd) in diploid, tetraploid and hexaploid wheats.

Uptake and retranslocation of leaf-applied radiolabeled cadmium (109Cd) was studied in three diploid (Triticum monococcum, AA), four tetraploid (Triticum turgidum, BBAA) and two hexaploid (Triticum aestivum, BBAADD) wheat genotypes grown for 9 d under controlled environmental conditions in nutrient solution. Among the tetraploid wheats, two genotypes were primitive (ssp. dicoccum) and two genotypes modern wheats (ssp. durum). Radiolabelled Cd was applied by immersing the tips (3 cm) of mature leaf into a 109Cd radiolabelled solution. There was a substantial variation in the uptake and export of 109Cd among and within wheat species. On average, diploid wheats (AA) absorbed and translocated more 109Cd than other wheats. The largest variation in 109Cd uptake was found within tetraploid wheats (BBAA). Primitive tetraploid wheats (ssp. dicoccum) had a greater uptake capacity for 109Cd than modern tetraploid wheats (ssp. durum). In all wheats studied, the amount of the 109Cd exported from the treated leaf into the roots and the remainder of the shoots was poorly related to the total absorption. For example, bread wheat cultivars were more or less similar in total absorption, but differed greatly in the amount of 109Cd retranslocated. The diploid wheat genotype 'FAL-43' absorbed the lowest amount of 109Cd, but retranslocated the greatest amount of 109Cd in roots and remainder of shoots. The results indicate the existence of substantial genotypic variation in the uptake and retranslocation of leaf-applied 109Cd. This variation is discussed in terms of potential genotypic differences in binding of Cd to cell walls and the composition of phloem sap ligands possibly affecting Cd transport into sink organs.

Effect of mineral nutritional status on shoot-root partitioning of photoassimilates and cycling of mineral nutrients.

Mineral nutrients taken up by the roots are, as a rule, transported in the xylem to the shoot, and photoassimilates transported in the phloem to the roots. According to the Thornley model of photosynthate partitioning, nutrient deficiencies should favour photosynthate partitioning to the roots. Examples are cited to show that this preferential partitioning is dependent on phloem mobility and hence on nutrient cycling from shoot to roots. Thus, root growth is enhanced under nitrogen and phosphorus deficiencies, but not under deficiencies of nutrients of low mobility in the phloem, such as calcium and boron. Enhanced root growth under nutrient deficiency relies on the import of both photosynthates and mineral nutrients. Cycling of mineral nutrients serves a number of other functions. These include the root supply of nutrients assimilated in the shoot (nitrate and sulphate reduction), maintenance of cation-anion balance in the shoot, providing an additional driving force for solute volume flow in the phloem and xylem, and acting as a shoot signal to convey nutrient demand to the root. Cycling of certain mineral nutrients through source leaves has a considerable impact on photosynthate export as demonstrated in impaired export under magnesium, potassium, or zinc deficiencies. Mineral nutrient deficiency can, therefore, affect photosynthate partitioning either directly via phloem loading and transport or indirectly by depressing sink demand.

Magnesium deficiency and high light intensity enhance activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase in bean leaves.

The influence of varied Mg supply (10-1000 micromolar) and light intensity (100-580 microeinsteins per square meter per second) on the concentrations of ascorbate (AsA) and nonprotein SH-compounds and the activities of superoxide dismutase (SOD; EC 1.15.11) and the H(2)O(2) scavenging enzymes, AsA peroxidase (EC 1.11.1.7), dehydroascorbate reductase (EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2) were studied in bean (Phaseolus vulgaris L.) leaves over a 13-day period. The concentrations of AsA and SH-compounds and the activities of SOD and H(2)O(2) scavenging enzymes increased with light intensity, in particular in Mg-deficient leaves. Over the 12-day period of growth for a given light intensity, the concentrations of AsA and SH-compounds and the activities of these enzymes remained more or less constant in Mg-sufficient leaves. In contrast, in Mg-deficient leaves, a progressive increase was recorded, particularly in concentrations of AsA and activities of AsA peroxidase and glutathione reductase, whereas the activities of guaiacol peroxidase and catalase were only slightly enhanced. Partial shading of Mg-deficient leaf blades for 4 days prevented chlorosis, and the activities of the O(2) (.-) and H(2)O(2) scavenging enzymes remained at a low level. The results demonstrate the role of both light intensity and Mg nutritional status on the regulation of O(2) (.-) and H(2)O(2) scavenging enzymes in chloroplasts.

Involvement of superoxide radical in extracellular ferric reduction by iron-deficient bean roots.

The recent proposal of Tipton and Thowsen (Plant Physiol 79: 432-435) that iron-deficient plants reduce ferric chelates in cell walls by a system dependent on the leakage of malate from root cells was tested. Results are presented showing that this mechanism could not be responsible for the high rates of ferric reduction shown by roots of iron-deficient bean (Phaseolus vulgaris L. var Prélude) plants. The role of O(2) in the reduction of ferric chelates by roots of iron-deficient bean plants was also tested. The rate of Fe(III) reduction was the same in the presence and in the absence of O(2). However, in the presence of O(2) the reaction was partially inhibited by superoxide dismutase (SOD), which indicates a role for the superoxide radical, O(2) ([unk]), as a facultative intermediate electron carrier. The inhibition by SOD increased with substrate pH and with decrease in concentration of the ferrous scavenger bathophenanthroline-disulfonate. The results are consistent with a mechanism for transmembrane electron transport in which a flavin or quinone is the final electron carrier in the plasma membrane. The results are discussed in relation to the ecological importance that O(2) ([unk]) may have in the acquisition of ferric iron by dicotyledonous plants.