Ecdysteroidostatin from the house fly,Musca domestica

Ovaries from house flies maintained on sucrose secrete large amounts of ecdysteroid when they are cultured with ovarian ecdysteroidogenic hormone, OEH. However, ovarian ecdysteroid secretion is reduced by incubation with both OEH and the ovarian ecdysteroidostatin (OES). A partially purified OES fraction from a semi-preparative reverse phase HPLC C₁₈ column caused a 98% inhibition of ovarian ecdysteroid secretion in vitro at a concentration of 0.8 equivalents per μl. Ovaries can be activated to produce ecdysteroid in vivo by feeding diet containing protein to flies maintained on sucrose. Ecdysteroid secretion was inhibited when the in vivo stimulated ovaries were cultured with OES. This suggests that OES does not interfere with the OEH activation mechanism, but blocks ovarian ecdysteroid synthesis or release. Furthermore, OES inhibition is reversible and ecdysteroid secretion resumes when OES is removed. Musca OES could explain the decrease in ecdysteroid levels found in flies after mid-vitellogenesis. Both adult male and female abdomens contain OES, but OES was not transferred to females during mating. Evidence is presented that OES is not a trypsin modulating oostatic factor. Arch. Insect Biochem. Physiol. 38:166–176, 1998. © 1998 Wiley-Liss, Inc.     

于家沟遗址鸵鸟蛋皮的人类利用特征

鸵鸟蛋皮是中国北方旧石器时代遗址中最常见的鸟类遗存。目前,限于蛋皮的样本量与保存状况,很少有研讨古人类是否能够食用鸵鸟蛋液或者利用鸵鸟蛋作为盛煮容器问题。本文以于家沟遗址第3b和4层出土的鸵鸟蛋皮为材料,从其 ¹⁴C年代、孵化状况、燃烧导致的颜色变化等方面,分析了古人类获取、消费和利用鸵鸟蛋的方式。结果显示,于家沟人既采集了鸵鸟蛋皮作为制作装饰品的原料,也可能获取了完整鸵鸟蛋,食其蛋液,用其蛋壳,并将整蛋作为容器进行了加热。     

Protostylid expression at the enamel-dentine junction and enamel surface of mandibular molars of Paranthropus robustus and Australopithecus africanus

Distinctive expressions and incidences of discrete dental traits at the outer enamel surface (OES) contribute to the diagnoses of many early hominin taxa. Examination of the enamel-dentine junction (EDJ), imaged non-destructively using micro-computed tomography, has elucidated the morphological development of dental traits and improved interpretations of their variability within and among taxa. The OES expressions of one of these dental traits, the protostylid, have been found to differ among African Plio-Pleistocene fossil hominin taxa. In this study protostylid expression is examined at the OES and at the EDJ of Paranthropus robustus (n = 23) and Australopithecus africanus (n = 28) mandibular molars, with the goals of incorporating EDJ morphology into the definition of the protostylid and assessing the relative contribution of the EDJ and enamel cap to its expression in these taxa. The results provide evidence a) of statistically significant taxon-specific patterns of protostylid morphology at the EDJ that are not evident at the OES; b) that in P. robustus, thick enamel reduces the morphological correspondence between the form of the protostylid seen at the EDJ and the OES, and c) that if EDJ images can be obtained, then the protostylid retains its taxonomic value even in worn teeth.     

Dental trait expression at the enamel-dentine junction of lower molars in extant and fossil hominoids

Discrete dental traits are used as proxies for biological relatedness among modern human populations and for alpha taxonomy and phylogeny reconstruction within the hominin clade. We present a comparison of the expression of lower molar dental traits (cusp 6, cusp 7, trigonid crest pattern, and protostylid) at the enamel-dentine junction (EDJ) in a variety of extant and fossil hominoid taxa, in order to assess the contribution of the EDJ to the morphology of these traits at the outer enamel surface (OES). Molars (n=44) were imaged nondestructively using high-resolution microCT, and three-dimensional surface models of the EDJ and OES were created to compare trait expression at each surface. Our results indicate that these dental traits originate at the EDJ, and that the EDJ is primarily responsible for their degree of expression at the OES. Importantly, variable trait morphology at the EDJ (often not easily recognizable at the OES) indicates that different developmental processes can produce traits that appear similar at the enamel surface, suggesting caution in intra- and intertaxonomic comparisons. The results also highlight the importance of the EDJ for understanding the morphological development of discrete traits, and for establishing graded scales of variation to compare trait frequency among groups for the purpose of taxonomic and/or phylogenetic analysis. Finally, this study demonstrates that imaging the EDJ of both worn and unworn fossil hominin teeth provides a novel source of information about tooth development and variation in crown morphology.     

Pleistocene geochronology and palaeothermometry from protein diagenesis in ostrich eggshells: implications for the evolution of modern humans.

Proteinaceous residues incorporated within the crystal structure of ostrich eggshells (OES) are retained without loss over geological time exceeding 10 million years. Degradation of the polypeptides, including hydrolysis to smaller peptide fragments and eventual release of free amino acids, decomposition, and racemization and epimerization occur at regular, predictable rates dependent on ambient temperature. The extent of isoleucine epimerization (aIle/Ile ratio) in OES follows linear first-order reversible kinetics in controlled-temperature laboratory simulations of time up to an aIle/Ile ratio in excess of 1.0. The hydrolysis of leucine also follows a predictable pattern, but deviates from first-order kinetics. A nonlinear mathematical model has been developed that adequately describes the pattern of leucine hydrolysis through a wide temperature range. Arrhenius parameters were derived from laboratory experiments combined with rate constant values found for 14C-dated OES from stratified caves in southern Africa. These parameters for isoleucine epimerization and leucine hydrolysis differ by ca. 10%, allowing the simultaneous solution of the two equations for temperature, independent of sample age. Although the uncertainty of the simultaneous temperature is relatively high (+/- 10 degrees C), it provides an effective means of identifying burned samples. If sample age is known, palaeotemperatures (the integrated thermal history experienced by an eggshell as opposed to an 'instantaneous' temperature) can be calculated with a precision of better than +/- 1 degrees C. The ages of levels at Border Cave, South Africa, from which anatomically modern human skeletal remains have been recovered, are dated by the extent of isoleucine epimerization in associated OES.(ABSTRACT TRUNCATED AT 250 WORDS)     

Model for the examination of evolutionary trends in tooth development

Through the use of serial computerized tomography (C-t) scans, two distinct developmental stages can be identified in mature teeth. C-t scans thus provide a non-destructive method for assessing growth within individual teeth, as well as for comparison of the development of modern and fossil teeth. The second deciduous molar (DM2) and first permanent molar (M1) resemble one another morphologically, despite differences in size and developmental rates. Thus, they provide an excellent model for studying variation in growth within an individual. To test the C-t method, we first examined a recent archaeological sample and then examined teeth from Skhul I. Serial C-t scans were used to compare two distinct developmental stages represented by the dentine-enamel junction (DEJ) and outer enamel surface (OES), respectively, in mandibular DM2 and M1 of 31 archaeological specimens. The difference in form and size between these two surfaces in and between teeth was calculated from intercusp distances measured at the DEJ and OES using the form distance matrix. Intercusp distances at the DEJ and OES of these teeth were then compared to their counterparts in the DM2 and M1 of Skhul I, taken here as representative of early anatomically modern Homo sapiens sapiens. Form differences between paired DM2 and M1 at the DEJ were smaller than those at the OES, supporting the hypothesis that differences between the two teeth increase throughout development. The increase in intercusp distances from the DEJ to OES was found to reflect the angulation of cusps relative to one another, rather than enamel thickness. Form differences between the Skhul DM2 and M1 were smaller than those observed in the recent series, and the recent M1 differed more than the DM2 from its fossil counterpart. The similarities found between the Skhul permanent and deciduous teeth and the recent DM2, may reflect a similar growth pattern. This would contribute to earlier crown completion in the fossil M1. Am. J. Phys. Anthropol. 102:283–294, 1997 © 1997 Wiley-Liss, Inc.     

Relationships of maternal body size and morphology with egg and clutch size in the diamondback terrapin,Malaclemys terrapin (Testudines: Emydidae)

Because resources are finite, female animals face trade‐offs between the size and number of offspring they are able to produce during a single reproductive event. Optimal egg size (OES) theory predicts that any increase in resources allocated to reproduction should increase clutch size with minimal effects on egg size. Variations of OES predict that egg size should be optimized, although not necessarily constant across a population, because optimality is contingent on maternal phenotypes, such as body size and morphology, and recent environmental conditions. We examined the relationships among body size variables (pelvic aperture width, caudal gap height, and plastron length), clutch size, and egg width of diamondback terrapins from separate but proximate populations at Kiawah Island and Edisto Island, South Carolina. We found that terrapins do not meet some of the predictions of OES theory. Both populations exhibited greater variation in egg size among clutches than within, suggesting an absence of optimization except as it may relate to phenotype/habitat matching. We found that egg size appeared to be constrained by more than just pelvic aperture width in Kiawah terrapins but not in the Edisto population. Terrapins at Edisto appeared to exhibit osteokinesis in the caudal region of their shells, which may aid in the oviposition of large eggs.     

胚后发育期臭腹腺蝗中的血细胞种类

应用血球计数器统计了胚后发育期臭腹腺蝗Zonocerus variegatus中存在的血细胞类型和数目。从1龄幼虫至成虫的发育阶段中共观察到6种血细胞类型,即原血细胞 （PRS）、 浆血细胞 （PLS）、粒细胞 （GRS）、珠血细胞 （SPS）、绛色细胞（OES） 和adipohaemocytes （ADS）。不过,在1龄幼虫期未发现OES。在这6种血细胞中,PLS的总平均数最高,OES的总平均数最低。成虫期的血细胞数目显著高于其他发育阶段（P<0.05）,而1龄幼虫和2龄幼虫期的血细胞数目不存在显著差异（P>0.05）。     

Dietary energy substrates reverse early neuronal hyperactivity in a mouse model of Alzheimer's disease

Deficient energy metabolism and network hyperactivity are the early symptoms of Alzheimer's disease (AD). In this study, we show that administration of exogenous oxidative energy substrates (OES) corrects neuronal energy supply deficiency that reduces the amyloid‐beta‐induced abnormal neuronal activity in vitro and the epileptic phenotype in AD model in vivo. In vitro, acute application of protofibrillar amyloid‐β_1–42 (Aβ_1–42) induced aberrant network activity in wild‐type hippocampal slices that was underlain by depolarization of both the neuronal resting membrane potential and GABA‐mediated current reversal potential. Aβ_1–42 also impaired synaptic function and long‐term potentiation. These changes were paralleled by clear indications of impaired energy metabolism, as indicated by abnormal NAD(P)H signaling induced by network activity. However, when glucose was supplemented with OES pyruvate and 3‐beta‐hydroxybutyrate, Aβ_1–42 failed to induce detrimental changes in any of the above parameters. We administered the same OES as chronic supplementation to a standard diet to APPswe/PS1dE9 transgenic mice displaying AD‐related epilepsy phenotype. In the ex‐vivo slices, we found neuronal subpopulations with significantly depolarized resting and GABA‐mediated current reversal potentials, mirroring abnormalities we observed under acute Aβ_1‐42 application. Ex‐vivo cortex of transgenic mice fed with standard diet displayed signs of impaired energy metabolism, such as abnormal NAD(P)H signaling and strongly reduced tolerance to hypoglycemia. Transgenic mice also possessed brain glycogen levels twofold lower than those of wild‐type mice. However, none of the above neuronal and metabolic dysfunctions were observed in transgenic mice fed with the OES‐enriched diet. In vivo, dietary OES supplementation abated neuronal hyperexcitability, as the frequency of both epileptiform discharges and spikes was strongly decreased in the APPswe/PS1dE9 mice placed on the diet. Altogether, our results suggest that early AD‐related neuronal malfunctions underlying hyperexcitability and energy metabolism deficiency can be prevented by dietary supplementation with native energy substrates.     

Spectroscopic and probe measurements of the electron temperature in the plasma of a pulse-periodic microwave discharge in argon

A pulse-periodic 2.45-GHz electron-cyclotron resonance plasma source on the basis of a permanent- magnet mirror trap has been constructed and tested. Variations in the discharge parameters and the electron temperature of argon plasma have been investigated in the argon pressure range of 1 × 10^–4 to 4 × 10^–3 Torr at a net pulsed input microwave power of up to 600 W. The plasma electron temperature in the above ranges of gas pressures and input powers has been measured by a Langmuir probe and determined using optical emission spectroscopy (OES) from the intensity ratios of spectral lines. The OES results agree qualitatively and quantitatively with the data obtained using the double probe.     

Determination of phosphorus impurity that directly affects quantification of microbial genomic DNA using inductively coupled plasma optical emission spectrometry

We prepared genomic DNA from human placenta, Escherichia coli, and Bacillus subtilis using various DNA extraction methods and quantified the genomic DNA using ultraviolet (UV) spectrophotometry, capillary electrophoresis (CE), and inductively coupled plasma optical emission spectrometry (ICP–OES). Application of ICP–OES unexpectedly led to a serious overestimation of phosphorus in B. subtilis genomic DNA prepared using cetyltrimethyl ammonium bromide (CTAB). Further investigations using reversed-phase high-performance liquid chromatography (RP–HPLC), ultra-performance liquid chromatography electrospray ionization tandem mass spectrometry (UPLC–ESI–MS/MS), and ³¹P nuclear magnetic resonance (NMR) identified the phosphorus impurity as lipoteichoic acid (LTA).     

Brief communication: Contributions of enamel‐dentine junction shape and enamel deposition to primate molar crown complexity

Molar crown morphology varies among primates from relatively simple in some taxa to more complex in others, with such variability having both functional and taxonomic significance. In addition to the primary cusps, crown surface complexity derives from the presence of crests, cuspules, and crenulations. Developmentally, this complexity results from the deposition of an enamel cap over a basement membrane (the morphology of which is preserved as the enamel‐dentine junction, or EDJ, in fully formed teeth). However, the relative contribution of the enamel cap and the EDJ to molar crown complexity is poorly characterized. In this study we examine the complexity of the EDJ and enamel surface of a broad sample of primate (including fossil hominin) lower molars through the application of micro‐computed tomography and dental topographic analysis. Surface complexity of the EDJ and outer enamel surface (OES) is quantified by first mapping, and then summing, the total number of discrete surface orientation patches. We investigate the relative contribution of the EDJ and enamel cap to crown complexity by assessing the correlation in patch counts between the EDJ and OES within taxa and within individual teeth. We identify three patterns of EDJ/OES complexity which demonstrate that both crown patterning early in development and the subsequent deposition of the enamel cap contribute to overall crown complexity in primates. Am J Phys Anthropol, 2010. © 2010 Wiley‐Liss, Inc.     

Structural and dynamical analysis of an engineered FhuA channel protein embedded into a lipid bilayer or a detergent belt

Engineered channel proteins are promising nano-components with applications in nanodelivery and nanoreactors technology. Because few of the engineered channel proteins have been crystallized, solution studies based on Neutron Scattering, Circular Dichroism and NMR play a major role. Consequently, the understanding of membrane proteins dynamics in water/detergent solutions or when embedded in a lipid membrane, can clarify how the environment affects protein behavior. In this study, molecular dynamics simulations of the FhuA Escherichia coli outer membrane channel protein and its engineered FhuA Δ1-159 variant have been performed in two different environments: a DNPC (1,2-dinervonyl-sn-glycero-3-phosphocholine) lipid bilayer and a water/OES (N-octyl-2-hydroxyethyl sulfoxide) detergent solution. Furthermore the FhuA Δ1-159 variant has been simulated in the open and closed states, the last induced by the presence of six 3-(2-pyridyldithio)-propionic-acid in the channel inner core. Differences in protein structural and dynamical behavior between the two environments have been found. Considering the FhuA protein characterized by an elliptical-cylindrical symmetry: (a) neither variations on the secondary structure nor axial deformation have been observed in any of the systems; (b) the ellipticity of the channel section (open state) and its fluctuations are enhanced in presence of water/OES, while diminished or suppressed in the DNPC bilayer; (c) the insertion of hydrophobic pyridyl groups into the FhuA Δ1-159 channel (closed state) induces a higher ellipticity in water/OES solution, while shifting to a circular section in the DNPC membrane; (d) the cork domain represented by the first 159 amino acids does not play a major role for protein stability.     

Trigonid crests expression in Atapuerca-Sima de los Huesos lower molars: Internal and external morphological expression and evolutionary inferences

Trigonid crest patterning in lower molars is distinctive among Late Pleistocene hominins such as Homo neanderthalensis, fossil Homo sapiens and modern humans. In this paper, we present an examination of trigonid crest patterning in the Middle Pleistocene permanent lower molar sample (n = 62) of Homo heidelbergensis from Sima de los Huesos (SH). Crest expression was assessed from 3D models of the enamel and the dentine surfaces that were produced using micro-computed tomography (microCT). The aims of our analysis are to: 1) characterize the pattern of trigonid crest expression at the outer enamel and enamel-dentine junction surfaces (OES and EDJ) of the SH sample, 2) evaluate the concordance of expression between both surfaces, and 3) place trigonid crest variation in the SH sample into a phylogenetic context. Our results reveal a greater variability in the expression of trigonid crests at the EDJ (14 types) compared to the OES (4 types). Despite this variability, in almost all cases the expression of a continuous mid-trigonid or distal crest at the OES corresponds with the expression of a continuous mesial/mid-trigonid or distal trigonid crest, respectively, at the EDJ. Thus, it is possible to predict the type of trigonid crest pattern that would be at the OES in the case of partially worn teeth. Our study points to increased variability in trigonid crest expression in M₃s compared to M₁s and M₂s. Moreover, our analysis reveals that the SH sample matches broadly the trigonid crest patterns displayed by H. neanderthalensis and differs from those exhibited by H. sapiens, particularly in the almost constant expression of a continuous middle trigonid crest at the EDJ. However, SH hominins also exhibit patterns that have not been reported in H. neanderthalensis and H. sapiens samples. Other aspects of the variability of the trigonid crest expression at the dentine are presented and discussed.     

A stem–loop structure directs oskar mRNA to microtubule minus ends

mRNA transport coupled with translational control underlies the intracellular localization of many proteins in eukaryotic cells. This is exemplified in Drosophila, where oskar mRNA transport and translation at the posterior pole of the oocyte direct posterior patterning of the embryo. oskar localization is a multistep process. Within the oocyte, a spliced oskar localization element (SOLE) targets oskar mRNA for plus end-directed transport by kinesin-1 to the posterior pole. However, the signals mediating the initial minus end-directed, dynein-dependent transport of the mRNA from nurse cells into the oocyte have remained unknown. Here, we show that a 67-nt stem–loop in the oskar 3′ UTR promotes oskar mRNA delivery to the developing oocyte and that it shares functional features with the fs(1)K10 oocyte localization signal. Thus, two independent cis-acting signals, the oocyte entry signal (OES) and the SOLE, mediate sequential dynein- and kinesin-dependent phases of oskar mRNA transport during oogenesis. The OES also promotes apical localization of injected RNAs in blastoderm stage embryos, another dynein-mediated process. Similarly, when ectopically expressed in polarized cells of the follicular epithelium or salivary glands, reporter RNAs bearing the oskar OES are apically enriched, demonstrating that this element promotes mRNA localization independently of cell type. Our work sheds new light on how oskar mRNA is trafficked during oogenesis and the RNA features that mediate minus end-directed transport.     

Morphology of the enamel-dentine junction in sections of anthropoid primate maxillary molars

The shape of the enamel-dentine junction (EDJ) in primate molars is regarded as a potential indicator of phylogenetic relatedness because it may be morphologically more conservative than the outer enamel surface (OES), and it may preserve vestigial features (e.g., cuspules, accessory ridges, and remnants of cingula) that are not manifest at the OES. Qualitative accounts of dentine-horn morphology occasionally appear in character analyses, but little has been done to quantify EDJ shape in a broad taxonomic sample. In this study, we examine homologous planar sections of maxillary molars to investigate whether measurements describing EDJ morphology reliably group extant anthropoid taxa, and we extend this technique to a small sample of fossil catarrhine molars to assess the utility of these measurements in the classification of fossil teeth. Although certain aspects of the EDJ are variable within a taxon, a taxon-specific cross-sectional EDJ configuration predominates. A discriminant function analysis classified extant taxa successfully, suggesting that EDJ shape may a reliable indicator of phyletic affinity. When considered in conjunction with aspects of molar morphology, such as developmental features and enamel thickness, EDJ shape may be a useful tool for the taxonomic assessment of fossil molars.     

Carabelli's trait revisited: An examination of mesiolingual features at the enamel-dentine junction and enamel surface of Pan and Homo sapiens upper molars

Carabelli’s trait is a morphological feature that frequently occurs on the mesiolingual aspect of Homo sapiens upper molars. Similar structures also referred to as Carabelli’s trait have been reported in apes and fossil hominins. However, the morphological development and homology of these mesiolingual structures among hominoids are poorly understood. In this study, we employ micro-computed tomography to image the enamel-dentine junction (EDJ) and outer enamel surface (OES) of Pan (n = 48) and H. sapiens (n = 52) upper molars. We investigate the developmental origin of mesiolingual features in these taxa and establish the relative contribution of the EDJ and enamel cap to feature expression. Results demonstrate that mesiolingual features of H. sapiens molars develop at the EDJ and are similarly expressed at the OES. Morphological variation at both surfaces in this taxon can satisfactorily be assessed using standards for Carabelli’s trait developed by the Arizona State University Dental Anthropology System (ASUDAS). Relative to H. sapiens, Pan has an even greater degree of correspondence in feature expression between the EDJ and OES. Morphological manifestations in Pan molars are not necessarily limited to the protocone and are best characterized by a lingual cingulum that cannot be captured by the ASUDAS. Cusp-like structures, similar to those seen in marked Carabelli’s trait expressions in H. sapiens, were not found in Pan. This study provides a foundation for further analyses on the evolutionary history of mesiolingual dental traits within the hominoid lineage. It also highlights the wealth of morphological data that can be obtained at the EDJ for understanding tooth development and for characterizing tooth crown variation in worn fossil teeth.     

Improving zinc accumulation in cereal endosperm using HvMTP1, a transition metal transporter

Zinc (Zn) is essential for all life forms, including humans. It is estimated that around two billion people are deficient in their Zn intake. Human dietary Zn intake relies heavily on plants, which in many developing countries consists mainly of cereals. The inner part of cereal grain, the endosperm, is the part that is eaten after milling but contains only a quarter of the total grain Zn. Here, we present results demonstrating that endosperm Zn content can be enhanced through expression of a transporter responsible for vacuolar Zn accumulation in cereals. The barley (Hordeum vulgare) vacuolar Zn transporter HvMTP1 was expressed under the control of the endosperm‐specific D‐hordein promoter. Transformed plants exhibited no significant change in growth but had higher total grain Zn concentration, as measured by ICP‐OES, compared to parental controls. Compared with Zn, transformants had smaller increases in concentrations of Cu and Mn but not Fe. Staining grain cross sections with the Zn‐specific stain DTZ revealed a significant enhancement of Zn accumulation in the endosperm of two of three transformed lines, a result confirmed by ICP‐OES in the endosperm of dissected grain. Synchrotron X‐ray fluorescence analysis of longitudinal grain sections demonstrated a redistribution of grain Zn from aleurone to endosperm. We argue that this proof‐of‐principle study provides the basis of a strategy for biofortification of cereal endosperm with Zn.     

Techniques for boron determination and their application to the analysis of plant and soil samples

This paper reviews techniques for determining B concentration and isotopic ratio and their application to soil and plant samples. Boron concentration has been determined utilising spectrophotometry, potentiometry, chromatography, flame atomic emission and absorption spectrometry, inductively coupled plasma (ICP) optical emission (OES) and mass spectrometry (MS), and neutron activation analysis using neutron radiography and prompt- activation analysis. Isotopic ratios of B have been measured by ICP–MS, thermal ionisation mass spectrometry (TIMS) and secondary ion mass spectrometry (SIMS). For isotopic measurements, TIMS and SIMS are more sensitive and provide higher degrees of accuracy and resolution than ICP–MS, however, extensive sample preparation and purification, and time-consuming measurements limit their usefulness for routine analyses.While the spectrophotometric technique using a colorimetric reaction of B with azomethine-H has been the most extensively applied B determination method for soil and plant samples, colorimetric methods, in general, suffer from numerous interferences and have poor sensitivity and precision. The prompt- method can determine B concentration in intact samples which enables this method to be especially useful for some applications in agriculture. Research involving B behaviour in plant and soil environments would benefit from this technology. In recent years, the use of ICP–OES and ICP–MS for B determination in plant and soil samples has grown tremendously. The application of ICP–OES brought a significant improvement in B analysis because of its simplicity, sensitivity and multielement detection capability. However, besides matrix interferences, the two most sensitive emission lines for B suffer strong spectral interference from Fe. The ICP–OES is not adequately sensitive for some nutritional work involving low B concentrations and B translocation studies using the isotope tracer technique.Plasma is one of the most effective analyte ionisers and MS is the most sensitive ion detector. Coupling of plasma with MS resulted in the development of plasma source MS technology (ICP–MS) which has outperformed all previous analytical methods for trace element determination. Boron determination by ICP–MS suffers no spectroscopic interferences, and is considered the most practical and convenient technique for B isotope determination. The ability of ICP–MS to measure isotopic ratios as well as B concentration enables: (1) B concentration determination by the isotope dilution method, (2) verification of B concentration by isotope fingerprinting in routine analysis and (3) determination of total B concentration as well as B isotope ratio in the same run for biological tracer studies. Therefore, ICP–MS is the method of choice among the present-day technologies for determining B concentration and a convenient method for B isotope determination. In recent years, new generations of plasma-source MS instruments have been developed using alternative plasma generation methods and high-resolution mass spectrometers. These instruments are expected to bring further improvements in accuracy, sensitivity and precision of B determination.     

Biotic stress induced demolition of thylakoid structure and loss in photoelectron transport of chloroplasts in papaya leaves.

Papaya mosaic virus (PMV) causes severe mosaic symptoms in the papaya (Carica papaya L.) leaves. The PMV-induced alterations in photosystem II (PS II) structure and photochemical functions were probed. An increase in chlorophyll a (Chl a) fluorescence polarization suggests pathogen-induced transformation of thylakoid membrane to a gel phase. This transformation in physical state of thylakoid membrane may result in alteration in topology of pigments on pigment-binding proteins as reflected in pathogen-induced loss in the efficiency of energy transfer from carotenoids to chlorophylls. The fast Chl a fluorescence induction kinetics of healthy and PMV-infected plants by F(O)-F(J)-F(I)-F(P) transients revealed pathogen-induced perturbation on PS II acceptor side electron transfer equilibrium between Q(A) and Q(B) and in the pool size of electron transport acceptors. Pathogen-induced loss in photosynthetic pigments, changes in thylakoid structure and decrease in the ratio of F(V)/F(M) (photochemical potential of PS II) further correlate with the loss in photoelectron transport of PS II as probed by 2,6-dichlorophenol indophenol (DCPIP)-Hill reaction. Restoration of the loss by 1,5-diphenyl carbazide (DPC), an exogenous electron donor, that donates electron directly to reaction centre II bypassing the oxygen evolving system (OES), leads towards the conclusion that OES is one of the major targets of biotic stress. Further, the data suggest that chlorophyll fluorescence could be used as a non-invasive handy tool to assess the loss in photosynthetic efficiency and symptom severity in infected green tissues vis-a-vis the healthy ones.