Rate of acropetal transport of the xylem stream in phaseolus vulgaris

Hate of acropetal movement of the xylem stream was measured in the petioles, epicotyls, and hypocotyls of bean plants. Loss of water by intact, transpiring plants was first determined gravimetrically. Next, volume of the functional xylem in various sections of the stems was determined using radioisotope dilution techniques. Rate at which the xylem stream renewed itself to account for the overall water loss of the plant served as the basis for flow rate values.     

Nitrogen assimilation in sunflower leaves and upward and downward transport of nitrogen

The assimilation of ammonium and nitrate nitrogen into amino acids of mature sunflower leaves and their transport to the other plant parts were investigated using nitrogen-15 as a tracer. In the leaf, to which ¹⁵N-labelled ammonium was vacuum-infiltrated, the ¹⁵N content of glutamine was always the highest of the amino acids tested and that of alanine was higher than that of glutamic acid and aspartic acid at 15 min after the infiltration. On the other hand in the leaf to which ¹⁵N-labelled nitrate was vacuum-infiltrated, the ¹⁵N content of glutamic acid and aspartic acid was superior to that of glutamine. The incorporation of ¹⁵N into serine was not active in the case of either ¹⁵N-labelled ammonium or nitrate. In the internodes above and below the treated leaf, through which photosynthates were transported into other parts, the ¹⁵N content of γ-aminobutyric acid and glutamine was markedly high when both nitrogen sources were supplied. There were no differences in the labelling patterns of amino acids between the upper and lower internodes. From these results it may be concluded that glutamine, glutamic acid, and aspartic acid play an important role in the assimilation of ammonium and nitrate nitrogen in leaves and that nitrogen is transported mainly in the forms of γ-aminobutyric acid and glutamine from the leaves to the other plant parts,     

Effects of anion channel blockers on xylem nitrate transport in barley seedlings

Abstract

Taxonomic characteristics in accumulating Co and Ni was investigated with 60 plant species (37 genera, 27 families) grown on granite derived soils containing slightly low level of available Co. Considerable variations in Co and Ni content were observed among plant !species with small differences with regard to sampling sites. Exceptionally high Co content (25 ppm on D.W. basis) was found in the leaves of Clethra barbinervis. The value was about 48 times higher than the lowest Co content species. Reasonably high Co content was found with some species in genera: Hydrangea and Viburunum. Ni was highly accumulated in the leaves of Sasa borealis (16 ppm) and in fruits of Clethra barbinervis (65 ppm). [Other Nirich species were especially found in genera: Struthiopteris, Hydrangea, Stewartia, Clethra, and Symplocos. High positive correlation (P<0.01) was found between the concentration of Co and Ni in plant species.     

Uptake,assimilation and transport of nitrogen compounds by plants

This paper reviews current knowledge and presents some new information on the metabolism of nitrogen in various species of higher plants.The role of the root system is considered. It is shown that the roots of many herbaceous and woody plants can manufacture organic compounds of nitrogen from the nitrate or other forms of inorganic nitrogen they absorb from the medium. The extent to which they do this varies greatly with the age and nutrition of the plant and with the environmental conditions under which it is growing. The relationship is examined between the synthetic activities of the root and its activity in upward transport of nitrogen to the shoot. The latter process takes place predominantly, if not exclusively, in the xylem, and in each species one or more nitrogen-rich compounds, e.g., amides, ureides and amino acids, carry the bulk of the nitrogen leaving the root. A second group of plants is described in which roots do not function to any extent in the reduction of nitrate.Consideration is given to the fate of recently absorbed nitrogen once it reaches the shoot system. An inorganic source such as nitrate, or molecules such as amides containing surplus amino groupings, are shown to serve as nitrogen sources for synthesis of amino acids required for protein synthesis. Some of these amino acids arise directly from the photosynthetic apparatus. Alternatively, surplus nitrogen arriving from the root may be stored in the shoot, from where it is drawn upon extensively if uptake by the root fails to keep pace with the shoot's demands for nitrogen.The transport system for nitrogen is examined for the whole plant. The classes of sources and sinks for nitrogen are described, and information presented on the types of nitrogenous solutes they receive from the xylem and phloem.     

Transformation and sorption of fipronil in urban stream sediments

Fipronil is an urban-use insecticide, and the increased use has led to its frequent detections in urban streams. Most studies on the environmental fate of fipronil so far have focused on soils, and little is known about its behavior in sediment-water systems. In this study, we investigated the transformation and sorption of fipronil in urban stream sediments from California, incubated under facultative and anaerobic conditions. Degradation of fipronil in sediments generally followed exponential decay kinetics, and the first-order half-lives of fipronil were only 4.6-18.5 days in anaerobic sediments. The persistence of fipronil under facultative conditions was considerably longer, with half-lives from 25 to 91 days. Sterilization generally decreased the dissipation of fipronil, indicating that microbial activity was an important factor in fipronil transformations in sediments. Under facultative conditions, fipronil sulfide and sulfone were observed, while only fipronil sulfide was detected in anaerobic samples. The sorption coefficient K d consistently increased with organic carbon contents of sediments. In the same sediment, K d usually also increased with contact time, suggesting decreased availability for aged residues. Results from this study showed that the stability of fipronil in sediments depends closely on the oxygen status and that due to the readily conversion of fipronil to the sulfone and sulfide metabolites, the overall risk assessment of fipronil in surface aquatic systems should take into consideration fipronil as well as its metabolites.     

Uptake and phloem transport of glucose-fipronil conjugate in Ricinus communis involve a carrier-mediated mechanism

Some compounds containing glucose are absorbed via the monosaccharide transporters of the plasma membrane. A glucose-fipronil conjugate, N-[3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazol-5-yl]-1-(β-d-glucopyranosyl)-1H-1,2,3-triazole-4-methanamine (GTF), has been synthesized in our previous work. GTF exhibits moderate phloem mobility in Ricinus communis. In the current paper, we demonstrate that the uptake of GTF by Ricinus seedling cotyledon discs is partly mediated by an active carrier system (K(m)1 = 0.17 mM; V(max)1 = 2.2 nmol cm(-2) h(-1)). Four compounds [d-glucose, sucrose, phloridzin, and carbonyl cyanide m-chlorophenylhydrazone (CCCP)] were examined for their effect on GTF uptake. Phloridzin as well as CCCP markedly inhibit GTF uptake, and d-glucose weakly competes with it. The phloem transport of GTF in Ricinus seedlings is found to involve an active carrier-mediated mechanism that effectively contributes to the GTF phloem loading. The results prove that adding a glucose core is a reasonable and feasible approach to confer phloem mobility to fipronil by utilizing plant monosaccharide transporters.     

Effects of symbiosis with Rhizobium fredii on transport of fixed nitrogen in the xylem of soybean plants

An experiment was conducted to identify the main nitrogenous compound transported in the xylem sap of soybean plants nodulated with Rhizobium fredii. Soybean (Glycine max L. Merr.) cultivars, wild type Bragg (nod⁺, fix⁺) and its nitrate tolerant, hypernodulating mutant ntsll16 (nod⁺⁺, fix⁺) were used for this experiment. These soybean plants were inoculated with a slowgrowing rhizobium, Bradyrhizobium japonicum USDAllO or fast-growing rhizobia consisting of a mixture of R. fredii USDA191, USDA193, and USDA-194 and grown in a phytotron under natural light and controlled temperature conditions. Xylem sap was collected from Bragg and ntsll16 plants at the flowering and pod elongation stages. Acetylene reduction activity per plant or per nodule weight was not different between soybean lines and inoculums. The composition of the nitrogenous compounds in the xylem sap was compared between the symbionts, with B. japonicum and R. fredii. At the flowering stage, ureide-N and amide-N accounted for 53 to 70% and 20 to 27% respectively of the total N in the sap collected from the plants inoculated either with B. japonicum or R. fredii. At the pod elongation stage, ureide-N and amide-N accounted for 74 to 85%, and 7 to 19% of total sap N. With the growth of the soybean plants, the ratio of ureide-N in the xylem sap increased. These results suggest that in the case of wild soybean and the hypernodulating mutant line nodulated by R. fredii, ureide is transported as the main nitrogenous compound of fixed nitrogen in the xylem sap in the same way as in plants nodulated with B. japonicum.     

茶树对可溶性有机和无机态氮的吸收与运转特性

【目的】 揭示亚热带茶树能否直接吸收利用分子态可溶性有机氮,探讨茶树吸收可溶性有机和无机氮后的运转特性差异。【方法】 采用13C、15N双标记甘氨酸、15N标记硫酸铵和15N标记硝酸钾为同位素示踪剂,采用茶树（黄金桂）幼苗为试验材料进行同位素示踪盆栽试验,用同位素质谱仪测定茶树植株地上和地下部的13C、15N丰度。【结果】 供试土壤施用13C、15N双标记甘氨酸态有机氮后,2 h和6 h茶苗地下部和整株中的13C增量/15N增量比值均接近于1:1的理论值;2 h和6 h茶苗地上部未检出13C增量,而72 h地上部13C增量达0.284 μmol/（g,DW）;施用铵态氮2 h、6 h和72 h茶苗地下部、地上部和整株中的15N增量均极显著高于施用硝态氮和甘氨酸态有机氮;施用铵态氮6 h茶苗地上部15N增量/地下部15N增量比率分别比硝态氮和甘氨酸态有机氮的比率高34.7%和65.0%,72 h茶苗地上部15N增量/地下15N增量比率分别比硝态氮和甘氨酸态有机氮的比率高88.6%和133.0%,差异均达极显著水平。【结论】 黄金桂茶苗具有从土壤中直接吸收利用甘氨酸分子态有机氮的能力,但吸收量不及铵态氮和硝态氮;吸收的可溶性分子态有机氮可以从茶树根系运转至地上部;不同形态氮素在茶树植株体内的迁移能力高低表现为:铵态氮>硝态氮>甘氨酸态氮,该研究结果进一步证明陆地生态系统植物直接吸收利用可溶性有机氮是普遍存在的现象。     

Elucidation of fipronil photodegradation pathways

The phenylpyrazole insecticide fipronil (I) photolyzes to its desthio product (II) in aqueous solution. However, the necessity of an intervening oxidation to a sulfone intermediate (III) has not been resolved, and the photodegradation products of II have not been identified. Using GC-MS, HPLC-UV/vis, electrospray MS, (19)F NMR, and GC-TSD, our objective was to characterize the photodegradation pathways of I, which would clarify the role of III, identify products of II, and explain unbalanced mass accounts in previous studies. Findings showed that II is formed directly and photochemically from I, confirmed by the greater stability of III (t(1/2) 112 h), and that successive oxidations of I to III and then a sulfonate (IV) comprise a second pathway. Compound II underwent photodechlorination, substitution of chlorine by trifluoromethyl, and pyrazole ring cleavage. This work is significant to understanding the photochemistry of novel phenylpyrazole pesticides in the environment.     

Regulation of xylem transport of calcium from roots to shoot of maize by growth-related demand

The aim of the present experiments was to study the effect of growth-related nutrient demand on Ca²⁺ translocation from roots to shoot of maize (Zea mays L.). The plants were grown under controlled environmental conditions in nutrient solution with constant Ca²⁺ supply. The growth-related demand for Ca²⁺ and other nutrients was modified by growing the plants with their apical shoot meristem either at air temperature (24°C/20°C day/night) or at 14°C. Reduction of the shoot meristem temperature (SMT) to 14°C decreased shoot growth without affecting root growth in the first five days, which diminished the growth-related demand of the shoot for nutrients per unit of roots. This decrease in shoot demand led to a reduction not only of Ca²⁺ translocation rates in intact transpiring plants but also of Ca²⁺ fluxes in the xylem exudate of decapitated plants. This indicates that the decrease in xylem flux of Ca²⁺ at low SMT was not only the result of low transpiration-related water flux, and thus possibly low apoplasmic bypass transport of Ca²⁺ into the stele. In decapitated plants precultured at low SMT, the water flux through the roots was diminished even more than Ca²⁺ flux, leading to a significant increase in the Ca²⁺ concentration of the exudate, and thus presumably an increase in the Ca²⁺ gradient between cytosol and apoplast of stelar parenchyma cells. When the osmotically driven water flux was reduced by addition of mannitol to the nutrient solution, Ca²⁺ concentration in the exudate markedly increased, whereas Ca²⁺ translocation was only slightly affected. From these results it is suggested that the decrease in Ca²⁺ translocation rates at low shoot demand was not related to low water flux but to direct effects on the capacity of Ca²⁺ transport mechanisms in the roots.     

Poly- and monoclonal antibody-based ELISAs for fipronil

An enzyme-linked immunosorbent assay (ELISA) for fipronil was developed by using polyclonal antibodies (pABs) or monoclonal antibodies (mABs), and its suitability of the determination of this analyte in spiked water samples was studied. The pABs-based assay showed I50 = 17.95 ppb, I90 = 203.40 ppb, and I10 = 0.066 ppb, whereas the mABs-based assay showed I50 = 5.99 ppb, I90 = 485.40 ppb, and I10 = 0.074 ppb. The recoveries of fipronil from tap water samples by pABs-based ELISA were 93.00-124.00% in the range of 0-500 ng/mL, and those obtained from the samples by mABs-based ELISA were 94.70-108.00%. Different types of water from pool, river, and sea were spiked at different levels (ranging form 0.1 to 10 microg/L) and were assayed by the indirect ELISA with mABs. The recoveries of fipronil by this ELISA were in the range of 80-120%. The results demonstrate that this assay is suitable for the quantitative detection of fipronil at trace levels in water samples.     

Mineral nutrient transport by sunflower seedlings grown under saline conditions (NaCl)

Sunflower seeds (Helianthus annuus L., cv. Dwarf) were grown with distilled water only or increasingly saline solutions (NaCl) to determine the influence of salinity on seedling growth and on the distribution of mineral nutrients obtained exclusively from cotyledons. Seedling growth was decreased by moderate (50mM) and high (100mM) concentrations of NaCl in the growth solution. Salinity generally decreased mineral transport (especially Fe, Mn, Mg, and Ca) from seed to seedling, except for K. Transport of Fe, Mg, and Ca to the aerial part was also markedly reduced.     

Foliar-applied glyphosate substantially reduced uptake and transport of iron and manganese in sunflower (Helianthus annuus L.) plants

Evidence clearly shows that cationic micronutrients in spray solutions reduce the herbicidal effectiveness of glyphosate for weed control due to the formation of metal-glyphosate complexes. The formation of these glyphosate-metal complexes in plant tissue may also impair micronutrient nutrition of nontarget plants when exposed to glyphosate drift or glyphosate residues in soil. In the present study, the effects of simulated glyphosate drift on plant growth and uptake, translocation, and accumulation (tissue concentration) of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were investigated in sunflower (Helianthus annuus L.) plants grown in nutrient solution under controlled environmental conditions. Glyphosate was sprayed on plant shoots at different rates between 1.25 and 6.0% of the recommended dosage (i.e., 0.39 and 1.89 mM glyphosate isopropylamine salt). Glyphosate applications significantly decreased root and shoot dry matter production and chlorophyll concentrations of young leaves and shoot tips. The basal parts of the youngest leaves and shoot tips were severely chlorotic. These effects became apparent within 48 h after the glyphosate spray. Glyphosate also caused substantial decreases in leaf concentration of Fe and Mn while the concentration of Zn and Cu was less affected. In short-term uptake experiments with radiolabeled Fe (59Fe), Mn (54Mn), and Zn (65Zn), root uptake of 59Fe and 54Mn was significantly reduced in 12 and 24 h after application of 6% of the recommended dosage of glyphosate, respectively. Glyphosate resulted in almost complete inhibition of root-to-shoot translocation of 59Fe within 12 h and 54Mn within 24 h after application. These results suggest that glyphosate residues or drift may result in severe impairments in Fe and Mn nutrition of nontarget plants, possibly due to the formation of poorly soluble glyphosate-metal complexes in plant tissues and/or rhizosphere interactions.     

Uptake,transport and assimilation of 15N-nitrate and 15N-ammonium in tea (Camellia sinensis L.) plants

¹⁵N studies were conducted using hydroponically grown tea (Camellia sinensis L.) plants to clarify the characteristics of uptake, transport and assimilation of nitrate and ammonium. From the culture solution containing 50 mg L^-1 N0₃-N and 50 mg L^-1 NH.-N, the uptake of NH₃-N after 24 h was twice as high as that of NO₃-N, while the uptake of N0₃-N from the culture solution containing 90 mg N0₃-N and 10 mg NH₃-N was twice that of NH₄-N. The presence of 0.4 mM Al had no significant effect on the N0₃-N and NH₄-N uptake from the culture solutions containing 50 mg L^-1 N0₃-N and 50 mg L^-1 NH₄-N, 90 mg L^-1 N0₃-N and 10 mg L^-1 NH₄-N or 99 mg L^-1 N0₃-N and 1 mg L^-1 NH₄-N. Transport of N0₃-derived N to young leaves was much more rapid than that of NH₄-derived NO₃ and NH₄-derived N was largely retained in the roots and lower stem. Young and mature shoots separated from the roots absorbed more N0₃-N than intact plants. Nitrate assimilation occurred in both, roots and young as well as mature leaves. Internal cycling of N0₃-derived Nand NH₄-derived N from one root part to another part was not appreciable after 28 h, suggesting that a longer of time is required for cycling in woody plants.     

玉米与赤霉素对向日葵列当种子萌发、防除以及对后茬作物向日葵生长的影响

向日葵列当(Orobanche cumana Wallr.)是一种根寄生草本植物,对向日葵等经济作物造成严重危害。为了减少向日葵列当对向日葵的寄生,降低土壤中向日葵列当种子库,本试验以新疆地区广泛种植的玉米品种‘京糯一号’和‘新玉57号’为研究材料,通过穴盘试验研究在不同时期(出苗后10 d和15 d)施加两种不同浓度赤霉素(10~(-4 )mol·L~(-1)和10~(-5 )mol·L~(-1))对上述两个品种玉米生长发育和分泌列当萌发刺激物质的影响;24 d后收集并提取玉米根系分泌物,用其进行刺激向日葵列当种子的萌发试验,从而筛选出刺激向日葵列当种子萌发能力较强的玉米品种进行盆栽试验。通过盆栽试验,在玉米种植后的不同时期(20 d和40 d)喷施10~(-4 )mol·L~(-1)赤霉素以探究玉米与赤霉素共同防除向日葵列当种子的效果,收获时(105 d后)采集玉米地上部、根和根际土样品,用其甲醇浸提液刺激向日葵列当种子萌发;次年在种植过玉米的盆中种植后茬作物向日葵,收获时测定向日葵的农艺指标并统计向日葵列当的出土数。结果表明:穴盘试验中施加赤霉素对玉米的株高有显著增高作用,对玉米根系分泌萌发刺激物质没有抑制作用,即在玉米生长时期可以施加10~(-4 )mol·L~(-1)和10~(-5 )mol·L~(-1)赤霉素。此外,‘新玉57号’根系分泌物的100倍稀释液刺激向日葵列当种子的萌发率显著高于‘京糯一号’,因此选取‘新玉57号’作为盆栽试验的玉米品种。盆栽试验中不同时期施加10~(-4 )mol·L~(-1)赤霉素,玉米株高同样显著高于对照,增长率分别为22.5%、19.1%。次年种植后茬作物向日葵,在第20 d向玉米施加赤霉素处理的盆中种植的向日葵的花盘直径比对照(种植玉米时不施加赤霉素)显著增加57.1%。与对照相比,在种植玉米后的20 d和40 d施加赤霉素的处理种植向日葵,向日葵列当的出土数分别是1.3个·盆~(-1)、1.8个·盆~(-1),分别降低76.4%和67.3%。因此,可以在玉米种植的后20 d和40 d施加10~(-4 )mol·L~(-1)赤霉素,与玉米共同诱导向日葵列当种子"自杀发芽",以减少向日葵列当对向日葵植株的危害。     

Cadmium accumulation and distribution in sunflower plant

Cadmium (Cd) accumulation and distribution was studied in sunflower (Helianthus annuus L., public line HA‐89) plant. From an uncontaminated sandy loam brown forest soil with 162 μg kg^‐1 HNO₃/H₂O₂ extractable Cd the HA‐89 sunflower public line accumulated 114 ug kg^‐1 Cd in its kernels under open field conditions. This value is rather low as compared to data found by others. Sandy loam brown forest soil was treated with 0, 1 or 10 mg kg^‐1 of Cd to study the interaction of this heavy metal with young sunflower plants in a greenhouse pot experiment. The fresh weight and dry matter accumulation of sunflower plant organs (roots, shoots, leaves or heads) was unaffected by cadmium treatment of soil. The nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), or zinc (Zn) uptake of sunflower plant organs was not influenced by lower or higher Cd‐doses, except sunflower heads where 10 mg kg^‐1 of Cd treatment of soil significantly reduced the uptake of Ca, Fe, and Mn. Although Cd reduced the Zn uptake of roots, its rate was statistically not significant. Cadmium was accumulated prevalently in roots (1.21 mg kg^‐1,4.97 mg kg^‐1, or 13.69 mg kg^‐1 depending on Cd‐dose), and its concentration increased also in shoots or leaves. In spite of the short interaction time, elevated concentrations of cadmium (0.78 mg kg^‐1, 1.34 mg kg^‐1, or 3.02 mg kg^‐1 depending on Cd‐dose) were detected in just emerged generative organs (heads) of young sunflower plants.     

内蒙古典型生态区不同类型向日葵氮肥响应差异

利用2006～2016年内蒙古向日葵"3414"田间试验数据,评估食用向日葵和油用向日葵在不同生态区之间的氮肥响应及其差异,并分析土壤基础供氮能力对向日葵氮肥效应的影响。结果显示:推荐施氮条件下,食用向日葵在河套灌区、阴山北麓区和燕山丘陵区的施氮增产幅度分别为35.1%、47.6%和35.5%,偏生产力分别为24.1、22.8和22.7 kg/kg,农学利用率分别为5.6、6.6和5.7 kg/kg;油用向日葵在河套灌区、大兴安岭南麓区和燕山丘陵区的施氮增产幅度分别为32.8%、39.3%和18.9%,偏生产力分别为26.2、39.7和37.7 kg/kg,农学利用率分别为5.6、10.8和6.0 kg/kg。食葵和油葵的100 kg籽粒吸氮量均值分别为4.6和4.7 kg,吸收利用率分别为30.1%和38.9%,生理利用率分别为20.3和20.8 kg/kg。上述结果表明,内蒙古食葵施氮的增产效果优于油葵,食葵产量对外源氮肥的依赖程度也高于油葵,因而食葵相较于油葵更应重视氮肥的管理和调控;不同生态区自然环境和土壤地力的差异也显著影响了向日葵的氮肥增产效应,河套灌区应积极进行土壤培肥,燕山丘陵区和大兴安岭南麓区可适当增加施氮量,阴山北麓区则应以维持向日葵需求为标准适当减少施氮量。     

Petiole and leaf nitrate studies in sunflower

Abstract

This study was conducted at two sites in Mississippi to determine whether petiole and leaf NO^‐ ₃ monitoring could be used as a management tool in making fertilizer N recommendations for sunflower (Hellanthus annuus L.). Petiole and leaf samples were taken at the four leaf stage at both sites, and later at two week intervals at Brooksville. Petiole and leaf NO^‐ ₃ at the four leaf stage was significantly influenced by rate of N application at both sites. The level of petiole and leaf NO^‐ ₃ was highly correlated with rate of N application as well as with seed yield. The concentration of NO^‐ ₃ in petioles and leaves was greatest at the four leaf stage and showed quadratic declines as the season progressed. Petiole and leaf NO^‐ ₃ showed the highest correlations with rate of N application and seed yield at the four leaf stage than at any other sampling time at Brooksville, indicating that this was the “best” period for taking petiole and leaf samples. However, analysis of petioles and leaves at the four leaf growth stage for NO^‐ ₃ may have limited potential of becoming a useful tool in making N fertilizer recommendations for sunflower. This is due to the sensitivity of both petiole and leaf NO^‐ ₃ to time of sampling and locational differences, as well as lack of information on response of sunflower to N applied after this stage of growth.