Effect of experimentally induced calcium deficiency on the developmental expression of collagen types in chick embryonic skeleton

In order to investigate the effect of embryonic calcium deficiency on the cellular differentiation processes in embryonic skeletogenesis, chick embryos were maintained in long-term shell-less cultures in vitro. The absence of the eggshell, which normally provides over 120 mg of calcium to the embryo during the course of development, resulted in severely retarded and anomalous skeletal formation. The pattern of cytodifferentiation in the skeletal elements during development was assessed by examining collagen type synthesis in both endochondral and intramembranous bones of normal and shell-less embryos as a function of developmental age. Skeletal tissues obtained from these embryos at various developmental stages were maintained in short-term organ culture in medium containing [³H]Pro. The metabolically labeled collagen was isolated from these tissues and typed biochemically based on electrophoresis, ion-exchange chromatography, differential salt fractionation, zone precipitation chromatography, and CNBr peptide mapping. The results indicate that, compared to chronologically equivalent normal controls, calcium-deficient skeletal elements from shell-less embryos appeared to fail to mature into complete bony tissues and instead exhibited partial cartilage phenotype with the expression of cartilage-specific type II collagen.     

AN ANALYSIS OF HETEROCHROMATIN IN MAIZE ROOT TIPS

The B chromosomes of maize are condensed in appearance during interphase and are relatively inert genetically; therefore they fulfill the definition of heterochromatin. This heterochromatin was studied in root meristem cells by radioautography following administration of tritiated thymidine and cytidine, and was found to behave in a characteristic way, i.e. it showed asynchronous DNA synthesis and very low, if any, RNA synthesis. A cytochemical comparison of normal maize nuclei with nuclei from isogenic maize stock containing approximately 15–20 B-chromosomes in addition to the normal complement has revealed the following: (a) the DNA and histone contents are greater in nuclei with B chromosomes; (b) the proportion of DNA to histone is identical with that of nuclei containing only normal chromosomes; (c) the amount of nonhistone protein in proportion to DNA in interphase is less in nuclei with B chromosomes than in normal nuclei. In condensed B chromosomes the ratio of nonhistone protein to DNA is similar to that in other condensed chromatin, such as metaphase chromosomes and degenerating nuclei. The B chromosomes appear to have no effect on nucleolar RNA and protein. Replication of B chromosomes is precisely controlled and is comparable to that of the ordinary chromosomes not only in synthesis for mitosis but also in formation of polyploid nuclei of root cap and protoxylem cells.     

Fluctuations in human serum lipoproteins during the normal menstrual cycle

1. Lipoproteins were measured in sera from 11 young women having a similar environment and diet. Sera were obtained at weekly intervals over a 12-week period. The values of the lipoproteins during periods in the normal ovulatory cycle were compared to assess their relation to reported hormone concentrations in blood. 2. Only the 4–0s_f (HDL₂) (d 1·125 sodium chloride) fraction changed significantly; it increased at ovulation in ten of the 11 subjects and fell as menstruation approached. 3. There was greater variability in most of the low-density rather than the high-density lipoproteins within individuals. The lipoprotein class most characteristic for an individual was the 4–0s_f or HDL₂ fraction.     

Spatial and temporal variation in carbon isotope discrimination in prairie graminoids

We present the results of a 5-year examination of variation in the stable carbon isotope composition () of three C₃ graminoid species from a Sandhills prairie: Agropyron smithii, Carex heliophila and Stipa comata. Although consistent species-specific patterns for mean were seen, there was also significant and substantial among-year and within-season variation in . A smaller contribution to variation in came from topographic variation among sampling sites. Effects of species, year, season and topography contribute to variation in in an additive manner. An association between climate and exists that is consistent with previous work suggesting that reflects the interplay between photosynthetic gas exchange and plant water relations. Within the growing season, the time over which integrates plant response to the environment ranges from days to months.     

Binding of anti-H-Y monoclonal antibodies to separated X and Y chromosome bearing porcine and bovine sperm

Studies designed to answer the question whether or not H-Y antigen is preferentially expressed on Y chromosome bearing sperm have resulted in conflicting results. This is probably due to the absence of reliable methods for estimating the percentage of X and Y chromosome bearing sperm in fractions, enriched or depleted for H-Y antigen positive sperm. In recent years a reliable method for separating X and Y chromosome bearing sperm has been published. With this method, separation is achieved by using a flow cytometer/cell sorter, which detects differences in DNA content. This technique provided the first opportunity for testing anti-H-Y antibody binding to fractions enriched for X and Y chromosme bearing sperm, directly. A total of 7 anti-H-Y monoclonal antibodies were tested using sorted porcine sperm and in one experiment also sorted bovine sperm. All monoclonal antibodies bound only a fraction of the sperm (20 to 50%). However, no difference in binding to the X and Y sperm enriched fractions was found. Therefore, the present experiments do not yield evidence that H-Y antigen is preferentially expressed in Y chromosome bearing sperm. © 1993 Wiley-Liss, Inc.     

Early response of herbaceous vegetation to Rhododendron ponticum subsp. baeticum invasion in European Atlantic forests

Questions

Rhododendron ponticum subsp. baeticum is an invasive shrub of growing concern in continental Europe, but little is known about its impact on native plant communities. Here we ask: do environmental conditions differ between forest stands invaded by it and uninvaded stands? Do these differences correlate with R. ponticum's cover? Are these differences associated with differences in taxonomic and functional diversity of vascular plant species of the herb layer? Can these vegetation changes be explained by the sorting of certain life-history traits by R. ponticum-induced environmental changes?

Location

Several forests invaded by R. ponticum in the French Atlantic domain.

Methods

We recorded vegetation composition and a number of environmental variables in 400-m² plots that were established in 64 paired forest stands (32 invaded vs 32 uninvaded). We compiled traits from existing databases. We computed several metrics of taxonomic and functional diversity. We compared environmental variables and diversity metrics between invaded and uninvaded stands. We used correlation and regression analyses to relate them with R. ponticum's cover. We ran RLQ and fourth-corner analyses to explore the relationships between R. ponticum invasion, environmental variables, species traits, and vegetation composition.

Results

Independent of its abundance, R. ponticum invasion was associated with lower light arrival at the forest floor and increased litter thickness. Concomitantly, species richness and diversity and trait diversity were reduced. The major driver of species assemblages was soil pH, which strongly interacted with the invasion gradient. R. ponticum did not sort species according to traits associated with shade tolerance and thick-litter tolerance. However, tree and shrub saplings were more abundant in invaded than uninvaded stands, at the expense of graminoid and fern species.

Conclusions

As R. ponticum becomes the dominant shrub, it exerts new selection forces on life-history traits of extant species, mostly via reduced light availability, increased litter thickness, and physical competition, thereby reducing taxonomic and functional diversity of the herb layer, without impeding tree and shrub self-regeneration, at least in the short term.     

Expertise in expert systems: knowledge acquisition for biological expert systems

In this paper it is argued that an expert system requires morethan factual knowledge before it can display expertise in agiven domain. The additional knowledge consists of the heuristicsor ‘rules of thumb’ used by an expert to manipulateand interpret the factual knowledge. The knowledge acquisitionphase of an expert system project involves determining the factualknowledge (which may be obtained from published sources) andthe heuristics used by an expert to manipulate that knowledge-theseheuristics can only be obtained from an expert. In reviewingexisting biological expert systems it is apparent that manycontain only the factual knowledge relating to the domain, andlack the heuristics that enable such systems to show expertise.This paper reviews a number of knowledge acquisition techniqueswhich could be used for acquiring heuristic knowledge and discusseswhen their use is appropriate. The knowledge acquisition techniquesdiscussed are those suitable for the development of small-scaleexpert systems as these are most likely to be of interest tobiologists. The techniques include the use of questionnaires,interview techniques and protocol analysis; particular emphasisis placed on a mod cation to the ‘twenty questions’interview technique which was developed specifically to elicittaxonomic knowledge relating to water mite identification.     

Differential expression of two related amino acid transporters with differing substrate specificity in Arabidopsis thaliana

A general amino acid permease cDNA ( AAP2 ) was isolated from Arabidopsis by complementation of a yeast mutant defective in citrulline uptake. Direct transport measurements in yeast show that the protein mediates uptake of l -[¹⁴C]-citrulline and l -[¹⁴C]-proline. Detailed analyses of the substrate specificity by competition studies demonstrate that all proteogenic amino acids are recognized by the carrier, including those that represent the major transport forms of reduced nitrogen in many species, i.e. glutamine, glutamate and asparagine. Thus, AAP2 is less selective as compared with AAP1 and transports basic amino acids such as histidine as shown by expression in a histidine transport-deficient yeast strain. The predicted polypeptide of 53 kDa is highly hydrophobic with 12 putative membrane-spanning regions and shows significant homologies to the Arabidopsis broad specificity permease AAP1, and a limited homology to bacterial branched chain amino acid transporters, but not to any other known proteins. Alterations in the charged residues as compared with AAP1 in four regions might be involved in the difference in selectivity towards basic amino acids. Both genes are highly expressed in developing pods indicating a role in supplying the developing seeds with reduced nitrogen. AAP2 is selectively expressed in the stem and might therefore play a role in xylem-to-phloem transfer of amino acids during seed filling. Furthermore in situ hybridization shows that both genes are expressed in the vascular system of cotyledons in developing seedlings.