Localization of Nitrate Absorption and Translocation within Morphological Regions of the Corn Root

The absorption of NO₃⁻ was characterized in six regions of a 7-d-old corn root (Zea mays L. cv W64A × W182E) growing in a complete nutrient solution. Based on changing rates of ¹⁵N accumulation during 15-min time courses, translocation of the concurrently absorbed N through each region of the intact root was calculated and distinguished from direct absorption from the medium. Of the ¹⁵N accumulated in the 5-mm root tip after 15 min, less than 15 and 35% had been absorbed directly from the external solution at 0.1 and 10 mm NO₃⁻ concentration of the external solution, respectively. The characterization of the apical portion of the primary root as a sink for concurrently absorbed N was conconfirmed in a pulse-chase experiment that showed an 81% increase of ¹⁵N in the 5-mm root tip during a 12-min chase (subsequent to a 6-min labeling period). The lateral roots alone accounted for 60% of root influx and 70% of 15-min whole root ¹⁵N accumulation at either 0.1 or 10 mm. NO₃⁻ concentration of the external solution. Because relatively steady rates of ¹⁵N accumulation in the shoot were reached after 6 min, the rapidly exchanging pools in lateral roots must have been involved in supplying ¹⁵N to the shoot. The laterals and the basal primary root also showed large decreases (24 and 17%) in ¹⁵N during the chase experiment, confirming their role in rapid translocation.     

Plasminogen activator and collagenase production by cultured capillary endothelial cells

Cultured bovine capillary endothelial (BCE) cells produce low levels of collagenolytic activity and significant amounts of the serine protease plasminogen activator (PA). When grown in the presence of nanomolar quantities of the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA), BCE cells produced 5-15 times more collagenolytic activity and 2-10 times more PA than untreated cells. The enhanced production of these enzymes was dependent on the dose of TPA used, with maximal response at 10(-7) to 10(-8) M. Phorbol didecanoate (PDD), an analog of TPA which is an active tumor promoter, also increased protease production. 4-O-methyl-TPA and 4α-PDD, two analogs of TPA which are inactive as tumor promoters, had no effect on protease production. Increased PA and collagenase activities were detected within 7.5 and 19 h, respectively, after the addition of TPA. The TPA-stimulated BCE cells synthesized a urokinase-type PA and a typical vertebrate collagenase. BCE cells were compared with bovine aortic endothelial (BAE) cells and bovine embryonic skin (BES) fibroblasts with respect to their production of protease in response to TPA. Under normal growth conditions, low levels of collagenolyic activity were detected in the culture fluids from BCE, BAE, and BES cells. BCE cells produced 5-13 times the basal levels of collagenolytic activity in response to TPA, whereas BAE cells and BES fibroblasts showed a minimal response to TPA. Both BCE and BAE cells exhibited relatively high basal levels of PA, the production of which was stimulated approximately threefold by the addition of TPA. The observation that BCE cells and not BAE cells produced high levels of both PA and collagenase activities in response to TPA demonstrates a significant difference between these two types of endothelial cells and suggests that the enhanced detectable activities are a property unique to bovine capillary and microvessel and endothelial cells.     

The Early Entry of Al into Cells of Intact Soybean Roots (A Comparison of Three Developmental Root Regions Using Secondary Ion Mass Spectrometry Imaging)

Al localization was compared in three developmental regions of primary root of an Al-sensitive soybean (Glycine max) genotype using secondary ion mass spectrometry. In cryosections obtained after a 4-h exposure to 38 [mu]M [Al3+], Al had penetrated across the root and into the stele in all three regions. Although the greatest localized Al concentration was consistently at the root periphery, the majority of the Al in each region had accumulated in cortical cells. It was apparent that the secondary ion mass spectrometry 27Al+ mass signal was spread throughout the intracellular area and was not particularly intense in the cell wall. Inclusion of some cell wall in determinations of the Al levels across the root radius necessitated that these serve as minimal estimates for intracellular Al. Total accumulation of intracellular Al for each region was 60, 73, and 210 nmol g-1 fresh weight after 4 h, increasing with root development. Early metabolic responses to external Al, including those that have been reported deep inside the root and in mature regions, might result directly from intracellular Al. These responses might include ion transport events at the endodermis of mature roots or events associated with lateral root emergence, as well as events within the root tip.     

The nutritional status of the apical meristem of Lactuca sativa as affected by NaCl salinization: An electron-probe microanalytic study

A volume of tissue of lettuce (Lactuca sativa L.) plants extending 2 mm basipetally from the apical meristem and including leaf primordia and young expanding leaves was surveyed using electron-probe microanalysis (EPMA) on both frozen-hydrated and freeze-dried samples. This analysis was carried out either 2 or 5 d following NaCl salinization of the medium from the 10 mol · m^–-3 control level up to 80 mol · m^–-3. The objective was the investigation of possible changes in the nutritional status of the apical meristem that might account for some aspects of salt-induced growth inhibition. Sodium and chloride increased significantly in tissues basal to the apical meristem, while both phosphorus and potassium decreased in the same region. These changes were evident in specimens collected just 2 d after the commencement of salinization (20 h after completion of the salinization) and were not exacerbated by an additional 3 d of treatment; they were present in tissue as close as 100 m to the meristem and extending down to 500 m. The apical 10–50 m were relatively protected from both the increase in sodium and chloride and the decrease in phosphorus and potassium that occurred in more basal regions. Young leaves (up to 1.5 mm in length) appear to control their own mineral nutrient levels when challenged by salinization of the medium, presumably because of altered growth. A decrease in the concentration of total Ca as a result of salinization was significant in cells 500 m basal to the meristem, but was evident as a tendency in the data even within the first 50 m. Using an improved automatic method for the analysis of calcium by EPMA, it was found that total Ca was reduced by salinization, especially in basal regions (500 m below the apex) and also in young leaves (1–1.5 mm in length). We suggest that the nutrition of the shoot apical meristem may be disturbed soon after salinization and that the shoot meristem might be the source of a signal to expanding leaves, as well as exerting its own direct influence over leaf emergence.Abbreviation EPMA electron-probe microanalysis This work was supported by U.S. Department of Agriculture grant 87-CRCR-1-2462.     

A common polygenic basis for quinine and PROP avoidance in mice

Inbred strains of mice (Mus musculus) differ greatly in ability to taste various bitter compounds. For some compounds, the differences result from allelic variation at a single locus. However, segregation patterns incompatible with monogenic inheritance have been found for quinine avoidance. The Soa bitter sensitivity locus exerts some influence on this phenotype, but an unknown number of other loci also contribute. Relative avoidance patterns for quinine sulfate in panels of naive inbred strains resembled avoidance patterns for 6-n-propyl-2- thiouracil (PROP), suggesting a common genetic basis. In particular, C57BL/6J mice strongly avoided both 0.1 mM quinine sulfate and 1 mM PROP in two-bottle preference tests, whereas C3H/HeJ mice were indifferent to both. Therefore, 12 BXH/Ty recombinant inbred strains, derived from these strains, were tested with both solutions to begin identification of the unknown bitter loci. Naive mice were tested for four consecutive days with each compound (order counterbalanced). Some BXH/Ty strain means resembled those of the parent strains, but others were intermediate. This indicated recombination among loci affecting avoidance, and therefore polygenic inheritance. The strain means were highly correlated across compounds (r = 0.98), suggesting that the same polygenes controlled both phenotypes. The BXH/Ty means for both compounds were then compared with the strain genotypes at 212 chromosome position markers distributed throughout the genome. Eight markers on five chromosomes (3, 6, 7, 8 and 9) yielded significant correlations. Six of the markers were correlated with both phenotypes, again suggesting common polygenic inheritance. The marker with the highest correlation was Prp, tightly linked to Soa on chromosome 6. The correlated marker regions likely contain quantitative trait loci affecting bitter avoidance. The phenotypic similarity of PROP to quinine, rather than to phenylthiourea, apparently stemming from a common polygenic basis, indicates a difference between mice and humans in gustatory organization related to bitters.      

The application of SIMS to nutrient tracer studies in plant physiology

Current controversies in root physiology relating to the uptake and translocation of mineral nutrients are presented. The opportunities for a SIMS contribution to resolve these controversies are discussed for each of the stable isotope tracers relevant to plant nutrition. It is concluded that for all major nutrients except phosphorus there are promising stable isotope tracers. At the same time, there are challenges to overcome in each case, with respect to background levels, peak interferences and sometimes sensitivity. Techniques of tissue preparation and handling are discussed in some detail, giving attention to the special requirements of plant tissue preparation and analysis for diffusable ions. It is suggested that adapting a preparation and transfer system, designed for production of bulk frozen-hydrated cryofractured specimens, to a secondary ion mass spectrometer would permit easy, rapid preparation. Additionally, this preparation minimizes several serious technical problems inherent to other preparative methods. Difficulties in quantitation are treated briefly, outlining some difficulties specific to plant tissue analysis. Prospects for future applications in plant mineral nutrition are evaluated, taking into account current instrumental developments.     

Diet-induced obesity in rats leads to a decrease in sperm motility

Background  

Obesity is rapidly becoming a worldwide epidemic that affects children and adults. Some studies have shown a relationship between obesity and infertility, but until now it remains controversial. Thus, the aim of the present study was to investigate the effect of high-fat diet-induced obesity on male reproductive parameters.     

A phylogenetic approach to the identification of phosphoglucomutase genes

The expanding molecular database provides unparalleled opportunities for characterizing genes and for studying groups of related genes. We use sequences drawn from the database to construct an evolutionary framework for examining the important glycolytic enzyme phosphoglucomutase (PGM). Phosphoglucomutase plays a pivotal role in the synthesis and utilization of glycogen and is present in all organisms. In humans, there are three well-described isozymes, PGMI, PGM2, and PGM3. PGM1 was cloned 5 years ago; however, repeated attempts using both immunological approaches and molecular probes designed from PGM1 have failed to isolate either PGM2 or PGM3. Using a phylogenetic strategy, we first identified 47 highly divergent prokaryotic and eukaryotic PGM-like sequences from the database. Although overall amino acid identity often fell below 20%, the relative order, position, and sequence of three structural motifs, the active site and the magnesium-- and sugar-binding sites, were conserved in all 47 sequences. The phylogenetic history of these sequences was complex and marked by duplications and translocations; two instances of transkingdom horizontal gene transfer were identified. Nonetheless, the sequences fell within six well-defined evolutionary lineages, three of which contained only prokaryotes. Of the two prokaryotic/eukaryotic lineages, one contained bacterial, yeast, slimemold, invertebrate, and vertebrate homologs to human PGM1 and the second contained likely homologs to human PGM2. Indeed, an amino acid sequence, derived from a partial human cDNA, that fell within the second cross-kingdom lineage bears several characteristics expected for PGM2. A third lineage may contain homologs to human PGM3. On a general level, our phylogenetic-based approach shows promise for the further utilization of the extensive molecular database.      

Incorporation of axonally transported glycoproteins into axolemma during nerve regeneration

The insertion of axonally transported fucosyl glycoproteins into the axolemma of regenerating nerve sprouts was examined in rat sciatic motor axons at intervals after nerve crush. [(3)H]Fucose was injected into the lumbar ventral horns and the nerves were removed at intervals between 1 and 14 d after labeling. To follow the fate of the “pulse- labeled” glycoproteins, we examined the nerves by correlative radiometric and EM radioautographic approaches. The results showed, first, that rapidly transported [(3)H]fucosyl glycoproteins were inserted into the axolemma of regenerating sprouts as well as parent axons. At 1 d after delivery, in addition to the substantial mobile fraction of radioactivity still undergoing bidirectional transport within the axon, a fraction of label was already associated with the axolemma. Insertion of labeled glycoproteins into the sprout axolemma appeared to occur all along the length of the regenerating sprouts, not just in sprout terminals. Once inserted, labeled glycoproteins did not undergo extensive redistribution, nor did they appear in sprout regions that formed (as a result of continued outgrowth) after their insertion. The amount of radioactivity in the regenerating nerves decreased with time, in part as a result of removal of transported label by retrograde transport. By 7-14 d after labeling, radioautography showed that almost all the remaining radioactivity was associated with axolemma. The regenerating sprouts retained increased amounts of labeled glycoproteins; 7 or 14 d after labeling, the regenerating sprouts had over twice as much of radioactivity as comparable lengths of control nerves or parent axons. One role of fast axonal transport in nerve regeneration is the contribution to the regenerating sprout of glycoproteins inserted into the axolemma; these membrane elements are added both during longitudinal outgrowth and during lateral growth and maturation of the sprout.     

Aluminum accumulation and associated effects on 15NO3 − influx in roots of two soybean genotypes differing in Al tolerance

A study was conducted to examine aluminum (Al) exclusion by roots of two differentially tolerant soybean (Glycine max L. Merr.) lines, Pl-416937 (Al-tolerant) and Essex (Al-sensitive). Following exposure to 80μM Al for up to 2 h, roots were rinsed with a 10 mM potassium citrate solution and rapidly dissected to allow estimation of intracellular Al accumulation in morphologically distinct root regions. Using 10 min exposures to 300μM ¹⁵NO₃ ⁻ and dissection, accompanying effects on NO₃ ⁻ uptake were measured. With Al exposures of 20 min or 2 h, there was greater Al accumulation in all root regions of Essex than in those of Pl-416937. The genotypic difference in Al accumulation was particularly apparent at the root apex, both in the tip and in the adjacent root cap and mucilage. Exposure of roots to Al inhibited the uptake of ¹⁵NO₃ ⁻ to a similar extent in all root regions. The results are consistent with Al exclusion from cells in the root apical region being an important mechanism of Al tolerance.