Concentrations of trace elements in the hair of the guinea pig

Various animal models have been employed for research on the significance of measuring trace element concentrations in the human scalp hair. The objects of such research were the establishment of relationships between the concentrations of trace elements in human scalp hair and (1) their concentrations in other compartments of the human body or (2) specific pathophysiological conditions. The guinea pig appears to be the animal of choice for such studies because the elemental composition and growth pattern of its hair parallel those of the human scalp hair.     

Can transposable element copy number distribution parameters be estimated from natural populations of Drosophila melanogaster?

The copy frequency distribution of a transposable element family in a Drosophila melanogaster natural population is generally characterised by the values of the Charlesworths' model parameters α and β (Charlesworth & Charlesworth, 1983). The estimation of these parameters is made using the observed distribution of the occupied sites in a population sample. Several results have been interpreted as due either to the influence of stochastic factors or to deterministic factors (transposition, excision, selection…). The accuracy of this method was tested by estimations performed on samples from simulated populations. The results show that with the sample size usually used for natural population studies, the confidence intervals are too large to reasonably deduce either the element copy number distribution or the values of transposition and excision rate and selective coefficients.     

FBXO44 promotes DNA replication-coupled repetitive element silencing in cancer cells

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Ontogeny of the proventitious epicormic buds in Quercus petraea.

In the present work, we described the fate of proventitious epicormic buds on the trunks of 40-year-old Quercus petraea trees and in parallel the vascular trace they produced in the wood. Our results show that small and large individual epicormic buds can survive as buds for 40 years and that both are composed of a terminal meristem and scales. Meristematic areas are detected in the scale axils of small buds; in addition to these meristems the large buds also have secondary bud primordia. The small buds are connected to the pith of the main stem by a unique trace, whereas the large buds are connected by one or multiple traces. A single trace might imply that the whole bud is still alive and multiple traces might indicate that the terminal meristem has died. In the latter case, each trace is connected to a secondary bud of the large bud. The buds found in a cluster are composed of a terminal meristem and scales with axillary meristems in the scale axils. A cluster is connected to the pith of a stem either by a unique trace when it seems to be the result of partial abscission of an epicormic shoot or multiple traces when it might have originated from an epicormic bud in which the terminal meristem has died. Whatever the type of the bud, the vascular trace in the bark is composed of a cambium, secondary xylem and parenchyma cells and the trace present in the wood had parenchyma cells with vestiges of secondary xylem. Each year, the vascular trace should be produced in the bark by the cambium of the tree but not by the bud itself. On 40-year-old Q. petraea, we observed a proliferation of epicormic buds and in parallel a multiplication of the number of vascular traces in the trunk, but the knots caused by the traces of epicormic buds in the wood, either as individuals or in clusters, are minor since their colours are only slightly darker than those of woody rays and they are less than 2 mm in diameter. The knots will appear when epicormic buds develop into shoots. Received: 30 March 1999 / Accepted: 09 June 1999     

A new lycopod, Novgorodendron conophorum gen. et sp. nov., from the Lower Carboniferous of the Moscow Syneclise

A new lycopod, Novgorodendron conophorum gen. et sp. nov., is described from the Upper Visean deposits of the Kamenka River, near the town of Borovichi (Novgorod Region). The morphology of the leaf cushions of the new plant implies its intermediate position between the families Sublepidodendraceae Chaloner et Boureau and Lepidodendraceae Endlicher. The bases of the leaf cushions have peculiar conical appendages, a previously unknown morphological feature not recorded from other lycopods. We propose the term basal conical appendages for them. The interpretation of some epidermal elements in the leaf cushions of the Lepidodendraceae is revised. The structures of the leaf cushions that were previously treated as either stomata or cells with cystoliths are shown to be sunken multicellular trichomes.     

Molybdenum in human whole blood of adult residents of the Merida State (Venezuela)

The concentration of molybdenum was measured in whole blood samples of 418 (244 males and 174 females) apparently normal donors ranging in age from 18 to 27-years old and living in nine different locations in the Mérida State (Venezuela). The geometric mean concentration of molybdenum of 418 subjects was of 2.66+/-0.66 microgL(-1) (range: 1.20-4.80 microgL(-1)). The levels of molybdenum in whole blood samples found in this work were of 2.57+/-0.52 and 2.54+/-0.51 (range: 1.20-4.80 and 1.40-4.20) microgL(-1) for males and females, respectively. The data of the content molybdenum in whole blood had no statistical correlation with age, sex or height above the sea level of the sampling sites. However, there was a tendency to decrease the levels of the element in those sampling sites located in highlands (> or = 1900 m above the sea level). This variability may be due to the source of molybdenum from the soil to the food chain that has affected its levels in donors from these areas under study. The results of this study are compared with values previously reported for subjects studied in other populations.     

Physiological interaction model of sunflower plant with its nutrient medium during ontogenesis

A study was conducted with sunflower plants (Helianthus annuus, L.) cv. Peredovik in field experiments, one of which included 9 NPK-fertilizer treatments. The intensity of uptake,i.e. the quantity (mg) of nutrient taken up for the accumulation of 1 g dry matter/day, the concentrations of all essential elements in the plant organ tissues and their distribution among above-ground organs, by stages of development, were investigated. The results have revealed the inherent physiological system responsible for the uptake intensity of individual elements, as well as the simultaneous uptake and distribution of all essential elements of the root nutrition by the shoots, throughout the life cycle of the plant.     

Reliability of the ICP-AES for trace elements studies of biological materials

In order to investigate the reliability of the Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) for trace element analysis of biological materials, we have carried out extensive investigations on human plasma, using an Applied Research Laboratory’s ICP-AES. When we aspirated the untreated plasma into the spectrometer, we obtained unreliable and nonreproducible results. However, when we pretreated the plasma by wet digestion (to destroy all the organic material), we achieved reproducible and consistent results. It is, therefore, suggested that biological samples should be pretreated, preferably by wet digestion, before being aspirated into the ICP-AES for analysis.     

Wound phloem in transition to bundle phloem in primary roots ofPisum sativum L.

Summary 48 hours after interrupting the root stele ofPisum, wound phloem initiated (proximally or distally to the wound) to reconnect the vascular stumps was found to contain some nucleate wound-sieve elements. At the elongating end of an incomplete wound-sieve tube these elements exhibit a sequence of ultrastructural changes as known from protophloem-sieve tubes. Elongation occurs by the addition of newly divided (wound-) sieve-element/companion-cell complexes. In order to dedifferentiate and assume a new specialization formerly quiescent stelar or cortical cells require at least one (mostly more) preliminary division. Companion cells are consequently obligatory sister cells to wound-sieve elements.By reconstruction using serial sections it could be shown that wound-sieve tubes elongate bidirectionally, starting in an early activated procambial cell of the stele. The elongation is directed by the existence of plasmodesmata, preferably when lying in primary pit fields, and by the plane of preceding divisions. Thus, the developing wound-sieve tube can deviate from the damaged bundle and radiate into the cortex as soon as the plane of the preceding divisions is favourable. In the opposite direction, elongating wound-sieve tubes run parallel to pre-existing phloem traces, thus broading their base at the bundle for the deviating part of the wound-sieve tube. Frequently an individual wound-sieve tube is supplemented at the bundle by a further wound-sieve tube which is partly running parallel to it. Both sieve tubes are interlinked with sieve plates by three-poled sieve elements.Ultrastructurally, the developmental changes of nucleate wound-sieve elements follow the known pattern. In spite of its contrasting origin and odd shape a mature wound-sieve element eventually has the same contents as regular sieve elements: sieve-element plastids, mitochondria, stacked ER and small amounts of P-protein within an electronlucent cytoplasm.