Changes in ion fluxes during phototropic bending of etiolated oat coleoptiles

BACKGROUND AND AIMS: This work has been conducted to assist theoretical modelling of the different stages of the blue light (BL)-induced phototropic signalling pathway and ion transport activity across plant membranes. Ion fluxes (Ca(2+), H(+), K(+) and Cl(-)) in etiolated oat coleoptiles have been measured continuously before and during unilateral BL exposure. METHODS: Changes in ion fluxes at the illuminated (light) and shadowed (dark) sides of etiolated oat coleoptiles (Avena sativa) were studied using a non-invasive ion-selective microelectrode technique (MIFE). The bending response was also measured continuously, and correlations between the changes in various ion fluxes and bending response have been investigated. For each ion the difference (Delta) between the magnitudes of flux at the light and dark sides of the coleoptile was calculated. KEY RESULTS: Plants that demonstrated a phototropic bending response also demonstrated Ca(2+) influx into the light side approximately 20 min after the start of BL exposure. This is regarded as part of the perception and transduction stages of the BL-induced signal cascade. The first 10 min of bending were associated with substantial influx of H(+), K(+) and Cl(-) into the light (concave) side of the coleoptiles. CONCLUSIONS: The data suggest that Ca(2+) participates in the signalling stage of the BL-induced phototropism, whereas the phototropic bending response is linked to changes in the transport of H(+), K(+) and Cl(-).     

Leaf water relations and net gas exchange responses of salinized Carrizo citrange seedlings during drought stress and recovery

BACKGROUND AND AIMS: Since salinity and drought stress can occur together, an assessment was made of their interacting effects on leaf water relations, osmotic adjustment and net gas exchange in seedlings of the relatively chloride-sensitive Carrizo citrange, Citrus sinensis x Poncirus trifoliata. METHODS: Plants were fertilized with nutrient solution with or without additional 100 mm NaCl (salt and no-salt treatments). After 7 d, half of the plants were drought stressed by withholding irrigation water for 10 d. Thus, there were four treatments: salinized and non-salinized plants under drought-stress or well-watered conditions. After the drought period, plants from all stressed treatments were re-watered with nutrient solution without salt for 8 d to study recovery. Leaf water relations, gas exchange parameters, chlorophyll fluorescence, proline, quaternary ammonium compounds and leaf and root concentrations of Cl(-) and Na(+) were measured. KEY RESULTS: Salinity increased leaf Cl(-) and Na(+) concentrations and decreased osmotic potential (Psi(pi)) such that leaf relative water content (RWC) was maintained during drought stress. However, in non-salinized drought-stressed plants, osmotic adjustment did not occur and RWC decreased. The salinity-induced osmotic adjustment was not related to any accumulation of proline, quaternary ammonium compounds or soluble sugars. Net CO(2) assimilation rate (A(CO2)) was reduced in leaves from all stressed treatments but the mechanisms were different. In non-salinized drought-stressed plants, lower A(CO2) was related to low RWC, whereas in salinized plants decreased A(CO2) was related to high levels of leaf Cl(-) and Na(+). A(CO2) recovered after irrigation in all the treatments except in previously salinized drought-stressed leaves which had lower RWC and less chlorophyll but maintained high levels of Cl(-), Na(+) and quaternary ammonium compounds after recovery. High leaf levels of Cl(-) and Na(+) after recovery apparently came from the roots. CONCLUSIONS: Plants preconditioned by salinity stress maintained a better leaf water status during drought stress due to osmotic adjustment and the accumulation of Cl(-) and Na(+). However, high levels of salt ions impeded recovery of leaf water status and photosynthesis after re-irrigation with non-saline water.     

蜂毒肽的溶血作用与红细胞膜上两种酶活性变化的关系

从蜂毒肽作用于红细胞膜上的Na^＋-K^＋-ATPase和葡萄糖-6-磷酸脱氢酶(G-6-PD)活性变化的角度,利用分光光度法测定酶活性,研究蜂毒肽与红细胞及膜作用过程中可能的靶点,讨论了蜂毒肽溶血过程与RBC膜上2种酶活性的变化．结果发现,蜂毒肽抑制RBC膜上酶活性的主要模式为附着/插入质膜与游离态并存模式,附着/插入质膜中的作用大于游离态的作用．Na^＋-K^＋-ATPase的K⁺结合位点是蜂毒肽的1个作用靶点．蜂毒肽插膜过程与其对此酶的作用随时间延长同步发生．蜂毒肽通过作用于葡萄糖-6-磷酸和NADP使G-6-PD的催化受到缓慢抑制,蜂毒肽形成四聚体的程度与酶活性密切相关．EDTA抑制蜂毒肽聚集,干扰蜂毒肽作用于G-6-P,蜂毒肽作用于底物G-6-P及辅酶NADP的生化机理相似,蜂毒肽抑制作用与G-6-PD的结构无关.     

Calcium in plants

Calcium is an essential plant nutrient. It is required for various structural roles in the cell wall and membranes, it is a counter-cation for inorganic and organic anions in the vacuole, and the cytosolic Ca2+ concentration ([Ca2+]cyt) is an obligate intracellular messenger coordinating responses to numerous developmental cues and environmental challenges. This article provides an overview of the nutritional requirements of different plants for Ca, and how this impacts on natural flora and the Ca content of crops. It also reviews recent work on (a) the mechanisms of Ca2+ transport across cellular membranes, (b) understanding the origins and specificity of [Ca2+]cyt signals and (c) characterizing the cellular [Ca2+]cyt-sensors (such as calmodulin, calcineurin B-like proteins and calcium-dependent protein kinases) that allow plant cells to respond appropriately to [Ca2+]cyt signals.     

高温胁迫对花生幼苗光合速率、叶绿素含量、叶绿体Ca2+-ATPase、Mg2+-ATPase及Ca2+分布的影响

将水培后盆栽的花生幼苗,置于培养箱42℃高温培养,定时测定幼苗叶光合速率、叶绿素含量和叶绿体Ca²⁺-ATPase、Mg²⁺-ATPase的相对活性,并观察幼叶细胞内Ca²⁺分布的变化。试验结果表明：高温胁迫过程中,光合速率及叶绿素含量都随处理时间的延伸而下降,并呈显著正相关;叶绿体Ca²⁺-ATPase和Mg²⁺-ATPase高温胁迫过程中相对活性呈先升后降趋势,Ca²⁺-ATPase热敏性高于Mg²⁺-ATPase;高温胁迫过程中,Ca²⁺具有从胞外转运到胞质内和叶绿体中的趋势,Ca²⁺能够稳定高温胁迫下叶肉细胞膜和叶绿体的超微结构。     

向日葵(Helianthus annuus L.)对133Cs、88Sr的吸收和分布

通过盆栽试验研究了向日葵(Helianthus annuus L.)对土壤中不同处理浓度¹³³Cs和⁸⁸Sr的吸收,以及¹³³Cs和⁸⁸Sr在向日葵不同部位的分布。结果表明：随着处理浓度的增加,植物中¹³³Cs或⁸⁸Sr的含量增加。同一处理浓度下,⁸⁸Sr含量约比¹³³Cs含量高一个数量级。¹³³Cs和⁸⁸Sr在植物不同部位分布不同。根部中¹³³Cs含量高于植物的其他部位（茎、叶、花）。不同于¹³³Cs在植物中的分布,⁸⁸Sr除在根中的分布外,主要转运到了叶片。¹³³Cs和⁸⁸Sr在向日葵体内的分布与目前对放射性¹³⁷Cs和⁹⁰Sr的研究结果相似,所以¹³³Cs和⁸⁸Sr可分别预测¹³⁷Cs和⁹⁰Sr的运转。向日葵是治理大面积低放核素污染土壤的较佳植物种类。     

Periplasm turgor pressure controls wall deposition and assembly in growing Chara corallina cells

BACKGROUND AND AIMS: New wall deposition usually accompanies plant growth. External osmotica inhibit both processes but wall precursors continue to be synthesized, and exocytosis follows. Consequently, the osmotica appear to act outside of the plasma membrane. Because this implies an action of turgor pressure (P) on the periplasm by unknown mechanisms, the following study was undertaken to determine whether P could act in a way that altered wall deposition and assembly in the periplasm while the cells grow. METHODS: Cells of Chara corallina were exposed to P slightly below normal by using a pressure probe while supplying inorganic carbon in light. After labelling, the walls were isolated and the amount of new wall was determined. Similar measurements were made after treatment with osmotica. Chlortetracycline-stimulated exocytosis was determined microscopically. Polysaccharide properties were determined by confocal microscopy and vapour pressure osmometry in an 'artificial periplasm' in isolated Chara cell walls, using labelled dextran as an analogue of hemicellulose, and polygalacturonate as pectin. KEY RESULTS: Rapid growth and wall deposition occurred at normal P of 0.5 MPa but both processes decreased when P was lowered 0.1 MPa. Inorganic carbon uptake and exocytosis were unaffected. In the artificial periplasm, normal P caused high polysaccharide concentrations and rapid polysaccharide entry into the wall, and gel formation in the pectin. Lowering P decreased entry and gel formation. CONCLUSIONS: This is the first indication that normal P of 0.5 MPa can concentrate periplasmic polysaccharides sufficiently to cause cross-linking and gel formation in pectins while simultaneously fostering the entry of large polysaccharides into small interstices in the existing wall. This P-action would thicken the primary wall and form a smooth transition between the new and old structure, suggesting a molecular mechanism of wall deposition and assembly while the wall extends.     

Evidence of phloem boron transport in response to interrupted boron supply in white lupin (Lupinus albus L. cv. Kiev Mutant) at the reproductive stage

The present study investigates whether previously acquired boron(B) in mature leaves in white lupin can be retranslocated intothe rapidly growing young reproductive organs, in response toshort-term (3 d) interrupted B supply. In a preliminary experimentwith white lupin in soil culture, B concentrations in phloemexudates remained at 300–500 µM, which were substantiallyhigher than those in the xylem sap (10–30 µM). Thehigh ratios of B concentrations in phloem exudates to thosein the xylem sap were close to values published for potassiumin lupin plants. To differentiate ‘old’ B in theshoot from ‘new’ B in the root, an experiment wascarried out in which the plants were first supplied with 20µM ¹¹B (99.34% by weight) in nutrient solution for 48d after germination (DAG) until early flowering and then transferredinto either 0.2 µM or 20 µM ¹⁰B (99.47% by weight)for 3 d. Regardless of the ¹⁰B treatments, significant levelsof ¹¹B were found in the phloem exudates (200–300 µMin 20 µM ¹⁰B and 430 µM in 0.2 µM ¹⁰B treatment)and xylem sap over the three days even without ¹¹B supply tothe root. In response to the 0.2 µM ¹⁰B treatment, thetranslocation of previously acquired ¹¹B in the young (the uppermostthree leaves), matured, and old leaves was enhanced, coincidingwith the rise of ¹¹B in the xylem sap (to >15 µM) andphloem exudates (430 µM). The evidence supports the hypothesisthat previously acquired B in the shoot was recirculated tothe root via the phloem, transferred into the xylem in the root,and transported in the xylem to the shoot. In addition, somepreviously acquired ¹¹B in the leaves may have been translocatedinto the rapidly growing inflorescence. Phloem B transport resultedin the continued net increment of ¹¹B in the flowers over 3d without ¹¹B supply. However, it is still uncertain whetherthe amount of B available for recirculation is adequate to supportreproductive growth until seed maturation. Key words: ¹⁰B, ¹¹B, B recirculation, Lupinus albus L., phloem exudate, xylem sap Received 9 October 2007; Revised 28 November 2007 Accepted 30 November 2007     

Incorporation of orally applied (13)C-galactose into milk lactose and oligosaccharides

Biosynthesis and functions of human milk oligosaccharides (HMO) are not well known. A typical housekeeping enzyme, beta1,4-galactosyltransferase, links galactose to glucose to form lactose which is then used as backbone for the assembly of HMO. We investigated whether milk lactose and HMO may be labeled in vivo by an orally given (13)C-galactose bolus. Eleven exclusively breastfeeding mothers were given a (13)C-galactose bolus at the end of their breakfast. Milk and urine samples from each nursing up to 36 h were analyzed for carbohydrate composition by high-performance thin-layer chromatography, high-pH anion-exchange chromatography, and fast atom bombardment mass spectrometry. (13)C enrichment of milk fractions, urinary carbohydrates, lactose, and oligosaccharides as well as of breath CO(2) was determined by isotope ratio mass spectrometry. Up to 10% of the orally given galactose bolus was directly transported to the mammary gland and incorporated into milk components. Characteristic for most milk samples was the appearance of two (13)C-peaks, the first immediately after the (13)C-bolus was taken and the second on the next morning. The highest (13)C enrichment was found in lactose followed by neutral and acidic oligosaccharides. In breath samples, the (13)C-excretion followed the same pattern as in milk. (13)C nuclear magnetic resonance of isolated lactose revealed (13)C only at C(1)-atom of galactose and C(1)-atom of glucose. This label was without any exception at the same position as the (13)C-label of the orally applied galactose. Neutral and acidic HMO can easily be (13)C-labeled in vivo which facilitates investigations of their metabolic fate in infants.     

Donor specificity in the glycosylation of Tamm-Horsfall glycoprotein: conservation of the Sda determinant in pairs of twins

The content of the Sd(a) determinant in urinary human Tamm-Horsfall glycoprotein (THp) has been reported to be donor-specific. This feature was further addressed by investigating THp from genetically identical individuals. To this end, THp was isolated from the urine of two monozygotic pairs of twins (A and B). The four samples (THp A1, A2, B1, and B2) were subjected to endo-beta-galactosidase from Bacteroides fragilis leading to the liberation of the Neu5Ac(alpha2-3)Gal (beta1-4)GlcNAc(beta1-3)Gal and Neu5Ac(alpha2-3)[GalNAc(beta1-4)] Gal(beta1-4)GlcNAc(beta1-3)Gal (Sd(a) epitope) motifs, both located at the nonreducing termini of complex type N-glycans. The isolated mixtures of oligosaccharides were analyzed for the absolute and relative amounts of the two oligosaccharides. The obtained data clearly indicate that in THp A1 and A2, and in THp B1 and B2, the molar ratios of the tetra- and Sd(a) pentasaccharide are identical for a pair of twins. This conservation of molar ratios points to an identical relative expression of beta-1,4-N-acetylgalactosaminyltransferase activity involved in the biosynthesis of the Sd(a) determinant. Apparently, the degree of conversion of the tetrasaccharidic Sd(a) precursor into the final pentasaccharidic Sd(a) form can be considered to result from a very closely related pattern of glycosylation for genetically homogeneous individuals.     

Intact cell adhesion to glycan microarrays

A rapid and reproducible method was developed to detect and quantify carbohydrate-mediated cell adhesion to glycans arrayed on glass slides. Monosaccharides and oligosaccharides were covalently attached to glass slides in 1.7-mm-diameter spots (200 spots/slide) separated by a Teflon gasket. Primary chicken hepatocytes, which constitutively express a C-type lectin that binds to nonreducing terminal N-acetylglucosamine residues, were labeled with a fluorescent dye and incubated in 1.3-microL aliquots on the glycosylated spots. After incubating to allow cell adhesion, nonadherent cells were removed by immersing the slide in phosphate buffered saline, inverting, and centrifuging in a sealed custom acrylic chamber so that cells on the derivatized spots were subjected to a uniform and controlled centrifugal detachment force while avoiding an air-liquid interface. After centrifugation, adherent cells were fixed in place and detected by fluorescent imaging. Chicken hepatocytes bound to nonreducing terminal GlcNAc residues in different linkages and orientations but not to nonreducing terminal galactose or N-acetylgalactosamine residues. Addition of soluble GlcNAc (but not Gal) prior to incubation reduced cell adhesion to background levels. Extension of the method to CD4+ human T-cells on a 45-glycan diversity array revealed specific adhesion to the sialyl Lewis x structure. The described method is a robust approach to quantify selective cell adhesion using a wide variety of glycans and may contribute to the repertoire of tools for the study of glycomics.     

Induction of HIV-1 resistance: cell susceptibility to infection is an inverse function of globotriaosyl ceramide levels

To examine the role of the glycosphingolipid (GSL), globotriaosylceramide(Gb₃, CD77, p^k blood group antigen) in HIV-1 infection, we havepharmacologically modulated Gb₃ metabolism in an X4 HIV-1 infectablemonocytic cell line (THP-1) that naturally expresses Gb₃ andin a Gb₃-expressing glioblastoma cell line (U87) transfectedto express both CD4 and CCR5 to permit R5 HIV-1 infection. THP-1and U87 cells were treated with either a competitive inhibitorof -galactosidase A, 1-deoxygalactonojirimycin (DGJ) to induceGb₃ accumulation, or a glucosylceramide synthase inhibitor,phenyl-2-palmitylamino-3-pyrrolidino-1-propanol (P4) to depletecells of Gb₃. HIV susceptibility was determined via measurementof p24^gag antigen production by ELISA. In addition, total cellularGb₃ content was determined using thin layer chromatography followedby Verotoxin1 overlay binding. The cell surface expression ofGb₃ was verified by FACS analysis. We found that DGJ significantlydecreased THP-1 and U87 cell susceptibility to HIV-1_IIIB andHIV-1_BaL infection, respectively, at a concentration of approximately100 µM. In contrast, P4 (2 µM) substantiallyincreased cellular susceptibility to HIV-1 infection. Totalcellular GSL analysis verified increased Gb₃ expression in cellstreated with DGJ and considerable reduction of Gb₃ in P4-treatedcells as compared to controls. These results show a reciprocalrelationship between Gb₃ expression and infection with eitherX4 HIV-1_IIIB or R5 HIV-1_Ba-L. These results support previousstudies that Gb₃ provides resistance to HIV infection. VariableGb₃ expression may provide a natural HIV resistance factor inthe general population, and pharmacological manipulation ofGb₃ levels may provide an approach to induction of HIV resistance.     

Lotus tenuis tolerates the interactive effects of salinity and waterlogging by 'excluding' Na+ and Cl- from the xylem

Salinity and waterlogging interact to reduce growth of poorly adapted species by, amongst other processes, increasing the rate of Na(+) and Cl(-) transport to shoots. Xylem concentrations of these ions were measured in sap collected using xylem-feeding spittlebugs (Philaenus spumarius) from Lotus tenuis and Lotus corniculatus in saline (NaCl) and anoxic (stagnant) treatments. In aerated NaCl solution (200 mM), L. corniculatus had 50% higher Cl(-) concentrations in the xylem and shoot compared with L. tenuis, whereas concentrations of Na(+) and K(+) did not differ between the species. In stagnant-plus-NaCl solution, xylem Cl(-) and Na(+) concentrations of L. corniculatus increased to twice those of L. tenuis. These differences in xylem ion concentrations, which were not caused by variation in transpiration between the two species, contributed to lower net accumulation of Na(+) and Cl(-) in shoots of L. tenuis, indicating that ion transport mechanisms in roots of L. tenuis were contributing to better 'exclusion' of Cl(-) and Na(+) from shoots, compared with L. corniculatus. Root porosity was also higher in L. tenuis, due to constitutive aerenchyma, than in L. corniculatus, suggesting that enhanced root aeration contributed to the maintenance of Na(+) and Cl(-) 'exclusion' in L. tenuis exposed to stagnant-plus-NaCl treatment. Lotus tenuis also had greater dry mass than L. corniculatus after 56 d in NaCl or stagnant-plus-NaCl treatment. Thus, Cl(-) 'exclusion' is a key trait contributing to salt tolerance of L. tenuis, and 'exclusion' of both Cl(-) and Na(+) from the xylem enables L. tenuis to tolerate, better than L. corniculatus, the interactive stresses of salinity and waterlogging.     

不同氮素形态比例对五味子幼苗生长特性的影响

以2年生五味子苗木为试验材料,在田间条件下,施以铵态氮(NH4+-N)和硝态氮(NO3--N)不同比例,分析了叶片可溶性蛋白、叶绿素含量、根系及茎叶中全氮含量、生物量等季节的动态变化规律,探讨了不同氮素形态比例对五味子苗木生长的影响。结果表明,五味子苗木在不同生长时期对不同氮素形态的吸收和利用存在明显差异,NH4+-N和NO3--N对五味子幼苗生长有显著的联合效应。在五味子生长前期,五味子主要以吸收和同化NH4+-N为主,并以铵态氮和硝态氮比例为75∶25时地上部生物量积累较多;而在五味子生长的中后期,五味子主要以NO3--N吸收和同化为主,并以铵态氮和硝态氮比例为25∶75时地上部生物量积累较多。     

Detoxification of dissolved SO2 (bisulfite) by terricolous mosses

BACKGROUND AND AIMS: The widespread calcifuge moss Pleurozium schreberi is moderately tolerant of SO2, whereas Rhytidiadelphus triquetrus is limited to calcareous soils in regions of the UK that were strongly affected by SO2 pollution in the 20th century. The proposition that tolerance of SO2 by these terricolous mosses depends on metabolic detoxification of dissolved bisulfite was investigated. METHODS: The capacities of the two mosses to accelerate loss of bisulfite from aqueous solutions of NaHSO3 were studied using DTNB [5, 5-dithio-(2-nitrobenzoic acid)] to assay bisulfite, and HPLC to assay sulfate in the incubation solutions. Incubations were performed for different durations, in the presence and absence of light, at a range of solution pH values, in the presence of metabolic inhibitors and with altered moss apoplastic Ca2+ and Fe3+ levels. KEY RESULTS: Bisulfite disappearance was markedly stimulated in the light and twice as great for R. triquetrus as for P. schreberi. DCMU, an inhibitor of photosynthetic electron chain transport, significantly reduced bisulfite loss. CONCLUSIONS: Bisulfite (SO2) tolerance in these terricolous mosses involves extracellular oxidation using metabolic (photo-oxidative) energy, passive oxidation by adsorbed Fe3+ (only available to the calcifuge) and probably also internal metabolic detoxification.     

Cluster Roots of Leucadendron laureolum (Proteaceae) and Lupinus albus (Fabaceae) Take Up Glycine Intact: An Adaptive Strategy to Low Mineral Nitrogen in Soils?

BACKGROUND AND AIMS: South African soils are not only low in phosphorus (P) but most nitrogen (N) is in organic form, and soil amino acid concentrations can reach 2.6 g kg(-1) soil. The Proteaceae (a main component of the South African Fynbos vegetation) and some Fabaceae produce cluster roots in response to low soil phosphorus. The ability of these roots to acquire the amino acid glycine (Gly) was assessed. METHODS: Uptake of organic N as 13C-15N-Gly was determined in cluster roots and non-cluster roots of Leucadendron laureolum (Proteaceae) and Lupinus albus (Fabaceae) in hydroponic culture, taking account of respiratory loss of 13CO2. KEY RESULTS: Both plant species acquired doubly labelled (intact) Gly, and respiratory losses of 13CO2 were small. Lupin (but not leucadendron) acquired more intact Gly when cluster roots were supplied with 13C-15N-Gly than when non-cluster roots were supplied. After treatment with labelled Gly (13C : 15N ratio = 1), lupin cluster roots had a 13C : 15N ratio of about 0.85 compared with 0.59 in labelled non-cluster roots. Rates of uptake of label from Gly did not differ between cluster and non-cluster roots of either species. The ratio of C : N and 13C : 15N in the plant increased in the order: labelled roots < rest of the root < shoot in both species, owing to an increasing proportion of 13C translocation. CONCLUSIONS: Cluster roots of lupin specifically acquired more intact Gly than non-cluster roots, whereas Gly uptake by the cluster and non-cluster roots of leucadendron was comparable. The uptake capacities of cluster roots are discussed in relation to spatial and morphological characteristics in the natural environment.