东北主要造林树种的营养元素含量特征分析

 本文分析测定了东北地区9个主要针阔叶树种的营养元素含量和季节动态,并应用主成分分析和系统聚类分析方法,分析了各树种之间的营养元素相互关系。从而证明了N,P,Ca是植物重要的临界营养元素,Fe和Mn是表土中高度积累元素,树木对前者的吸收与土壤表土中含量有关,而对后者则表现相对的独立性和选择吸收能力。从营养元素的吸收与利用角度考虑,红松与胡桃楸混交,落叶松与水曲柳混交,硬阔叶树与软阔叶树混交,针阔叶树之间混交或白桦与其它各树种混交都是合理的。     

Trace metals in the benthic habitat of the Maarsseveen Lakes system,The Netherlands

The cadmium, zinc, lead and copper concentrations in benthic invertebrates and sediment were determined during two consecutive winters in the Maarsseveen Lakes system. A sequential extraction procedure was applied to estimate the bioavailability of the trace metals in the sediment. Based on the trace metal analyses of organisms and sediment, it is concluded that the Maarsseveen Lakes system has background levels of cadmium, zinc, lead and copper. As the majority of metals was present in geochemically more stable sediment phases, the sequential extractions provided limited additional information on trace metal bioavailability.     

Inorganic chemical investigations in the Forest Biosphere Reserve near Kalinin,USSR

To get a first impression of the degree of pollution in the Forest Biosphere Reserve 350 km northwest of Moscow, samples of Polytrichum commune and peat profiles were measured by ICP/MS after decomposition by high-pressure ashing. Comparing the results with data found in similar systems in Central Europe the Forest Biosphere Reserve can be described than medium-polluted by heavy metals. Pb shows lower values as in comparable systems in Germany, due to the fact of lower traffic density in Sowjetunion. The status of the nutritional elements Ca, Mg and K is in the same order of magnitude as found in German forest ecosystems.     

The splicing of transposable elements and its role in intron evolution

Recent studies have demonstrated that transposable elements in maize and Drosophila are spliced from pre-mRNA. These transposable element introns represent the first examples of recent addition of introns into nuclear genes. The eight reported examples of transposable element splicing include members of the maize Ac/Ds and Spm/dSpm and the Drosophila P and 412 element families. The details of the splicing of these transposable elements and their relevance to models of intron origin are discussed.     

The suppressor of forked locus in Drosophila melanogaster: genetic and molecular analyses

The suppressor of forked, su(f) locus is one of a class of loci in Drosophila whose mutant alleles are trans-acting allele-specific modifiers of transposable element-insertion mutations at other loci. Mutations of su(f) suppress gypsy insert alleles of forked and enhance the copia insert allele white apricot. Our investigations of su(f) include genetic and molecular analyses of 19 alleles to determine the numbers and types of genetic functions present at the locus. Our results suggest the su(f) locus contains multiple genetic functions. There are two distinct modifier functions and two vital functions. One modifier function is specific for enhancement and the other for suppression. One vital function is required for normal ecdysterone production in the third larval instar, the other is not. We present a restriction map of the su(f) genomic region and the results of an RFLP analysis of several su(f) alleles.     

An Escherichia coli plasmid-based, mutational system in which supF mutants are selectable: Insertion elements dominate the spontaneous spectra

A new system is described to determine the mutational spectra of mutagens and carcinogens in Escherichia coli; data on a limited number (142) of spontaneous mutants is presented. The mutational assay employs a method to select (rather than screen) for mutations in a supF target gene carried on a plasmid. The E. coli host cells (ES87) are lacI⁻ (am26), and carry the lacZΔM15 marker for α-complementation in β-galactosidase. When these cells also carry a plasmid, such as pUB3, which contains a wild-type copy of supF and lacZ-α, the lactose operon is repressed (off). Furthermore, supF suppression of lacl^um26 results in a lactose repressor that has an uninducible, lacl^S genotype, which makes the cells unable to grow on lactose minimal plates. In contrast, spontaneous or mutagen-induced supF⁻ mutations in pUB3 prevent suppresion of lacl^am26 and result in constitutive expression of the lactose operon, which permits growth on lactose minimal plates. The spontaneous mutation frequency in the supF gene is 0.7 and 1.0 × 10⁻⁶ without and with SOS induction, respectively. Spontaneous mutations are dominated by large insertions (67% in SOS-uninduced and 56% in SOS-induced cells), and their frequency of appearance is largely unaffected by SOS induction. These are identified by DNA sequencing to be Insertion Element: IS1 dominates, but IS4, IS5, gamma-delta and IS10 are also obtained. Large deletions also contribute significantly (19% and 15% for - SOS and +SOS, respectively), where a specific deletion between a 10 base pair direct repeat dominates; the frequency of appearance of these mutations also appears to be unaffected by SOS induction. In contrast, SOS induction increases base pairing mutations (13% and 27% for -SOS and +SOS, respectively), The ES87/pUB3 system has many advantages for determining mutational spectra, including the fact that mutant isolation is fast and simple, and the determination of mutational changes is rapid because of the small size of supF.     

Root-microbial effects on plant iron uptake from siderophores and phytosiderophores

Collaborative experiments were conducted to determine whether microbial populations associated with plant roots may artifactually affect the rates of Fe uptake and translocation from microbial siderophores and phytosiderophores. Results showed nonaxenic maize to have 2 to 34-fold higher Fe-uptake rates than axenically grown plants when supplied with 1 μM Fe as either the microbial siderophore, ferrioxamine B (FOB), or the barley phytosiderophore, epi-hydroxymugineic acid (HMA). In experiments with nonsterile plants, inoculation of maize or oat seedlings with soil microorganisms and amendment of the hydroponic nutrient solutions with sucrose resulted in an 8-fold increase in FOB-mediated Fe-uptake rates by Fe-stressed maize and a 150-fold increase in FOB iron uptake rates by Fe-stressed oat, but had no effect on iron uptake by Fe-sufficient plants. Conversely, Fe-stressed maize and oat plants supplied with HMA showed decreased uptake and translocation in response to microbial inoculation and sucrose amendment. The ability of root-associated microorganisms to affect Fe-uptake rates from siderophores and phytosiderophores, even in short-term uptake experiments, indicates that microorganisms can be an unpredictable confounding factor in experiments examining mechanisms for utilization of microbial siderophores or phytosiderophores under nonsterile conditions.     

Photo-CIDNP study of the interaction between the glucocorticoid receptor DNA-binding domain and glucocorticoid response elements

Summary Photo-CIDNP studies were performed on two protein fragments that both contain the double zinc-finger DNA-binding domain of the glucocorticoid receptor. In the absence of DNA, Tyr⁴⁵² and Tyr⁴⁷⁴ are polarised in both fragments while Tyr⁴⁹⁷ is not. Addition of a palindromic glucocorticoid response element (GRE) results in the suppression of Tyr⁴⁷⁴ polarization while the polarization of Tyr⁴⁵² is unaffected. The same result is observed upon adding a half GRE to the protein fragment indicating that the suppression of Tyr⁴⁷⁴ polarization is not due to protein-protein contacts but to interaction with DNA.     

Sorption of hydrophobic organic contaminants and trace metals on phytoplankton and implications for toxicity assessment

The partitioning of trace metals and hydrophobic organic contaminants to phytoplankton determines their toxicity as well as their fate and transport in aquatic ecosystems. Accurate impact assessments, therefore, depend on a good understanding of the factors regulating the sorption of these compounds to biotic particles. The accumulation of chlorinated organic compounds in phytoplankton is generally considered as being due solely to physical sorption, described by reversible equilibrium models based on Langmuir or Freundlich isotherms. On the other hand, the uptake of trace metals is a two phase process: a fast sorption component viewed as an ionexchange or a covalent bonding process with cell surface ligands, followed by an intracellular transport phase that is dependent on cellular metabolic activity. The uptake of inorganic and hydrophobic organic pollutants and their bioaccumulation are influenced in a complex manner by duration of exposure and cell density, by environmental factors such as pH, the concentration of cations and of dissolved and colloidal organic matter, as well as by phytoplankton physiological condition. High concentrations of H⁺, Ca²⁺, and Mg²⁺ ions will reduce trace metal sorption by directly competing for uptake sites on the cell's surface, whereas the presence of dissolved organic carbon such as natural and synthetic chelators and phytoplankton exudates will reduce the bioavailability of both trace metals and hydrophobic organic contaminants. Thus, the impact of toxic contaminants on phytoplankton may be determined as much by the factors influencing uptake and partitioning as by the potency of the toxicants and interspecies differences in sensitivity. Recommendations for improving toxicity assessments are presented.     

Ontogeny of the vascular system ofBotrychium multifidum (S. G. Gmelin) Rupr.(Ophioglossaceae) and its bearing on stellar theories

Basipetal to the shoot apex, a procambial ring with parenchymatous gaps is present. The protoxylem poles are endarrh in both the ectophloic siphonostele and the collateral vascular bundle which comprises the leaf trace. Each leaf trace has an anastomosing system of protoxylem poles that decreases in number basipetally from five to three to two. Differentiation of the leaf trace procambium and protoxylem is bidirectional, that is the differentiation first occurs near the base of the leaf and acropetally in the leaf and basipetally in the stem. Then a fascicular cambium differentiates betweem the primary xylem and phloem in the leaf. This vascular cambium which is also present in the stem is unidirectional and only produces secondary xylem centripetally. Limited secondary growth also occurs in roots. Medullary tracheids when present are longitudinally continuous with the vascular system. The stele of the stem is interpretated as a sympodium of leaf traces and the pith is considered to be fundamental tissue enclosed by the anastomosing of leaf traces.