Species composition and vegetation structure of an upper montane forest at the summit of Mt. Doi Inthanon, Thailand

Upper montane forest (UMF) within Doi Inthanon National Park, Northern Thailand, was investigated by means of fifty, 40 × 40 m stratified random plots situated between 2080 and 2565 m altitude. The aim was to address a number of community ecological questions concerning woody species composition and structural heterogeneity of the forest. A total of 7474 individuals of trees and woody climbers ≥ 15 cm gbh (girth at breast height) were included in the study and these were identified to 47 species, 39 genera and 26 families. The average density was 934 individuals/ha and the average stem basal area was 71.8 m²/ha. The most important species were: Quercus eumorpha, Sjzygium angkae, Litsea martabanica, Helicia nilagirica, Lindera caudata, Schima wallichii, Osmanthus fiagrans, Eurya acuminata, Myrsine semiserrata and Ilex umbellulata and the most important families were Fagaceae, Lauraceae, Theaceae and Myrtaceae. Altitude was the most important environmental variable explaining species composition and vegetation structure. Most of the calculated vegetation variables showed significant correlation with altitude: species richness, family richness, diversity, density and crown cover declined with altitude, average tree height was uncorrelated with altitude and basal area increased with altitude. An analysis of size class distributions indicated good forest conditions and reverse-J-shaped age class distribution of most species.     

NMR imaging of roots: effects after root freezing of containerised conifer seedlings

Seedlings of Scots pine ( Pinus sylvestris L.) and Norway spruce [ Picea abies (L) Karst.] were subjected to low root temperatures, and 10 days later the roots were examined by NMR imaging. The amount of NMR detectable roots decreased with decreasing temperature, with the signal from the younger roots at the bottom of the container being the first to disappear. The origin of the loss of NMR signal is unclear but may be due to changes in the NMR properties of root water after cold damage. A recent method is discussed for obtaining unbiased estimates of root lengths from a series of total vertical projections; the method is particularly suited to evaluating NMR projection images. Since NMR imaging methods can apparently distinguish between control and cold damaged roots, it may be possible to design more routine applications using low resolution NMR methods.     

The floral development and floral anatomy ofChrysosplenium alternifolium, an unusal member of the Saxifragaceae

The floral development and anatomy ofChrysosplenium alternifolium were studied with the scanning electron microscope and light microscope to understand the initiation sequence of the floral organs and the morphology of the flower, and to find suitable floral characters to interpret the systematic position of the genus within the Saxifragaceae. The tetramerous flower shows a highly variable initiation sequence. The median sepals and first stamens arise in a paired sequence resembling a dimerous arrangement, but the first sepal and stamen arise on the side opposite to the bract. Transversal sepals and stamens emerge sequentially, as one side often precedes the other; sepals and stamens occasionally arise on common primordia. Initiation of the gynoecium is more constant with two median carpel primordia arising on a sunken floral apex. Several flowers were found to be pentamerous with a 2/5 initiation sequence. Flowers were invariably found to be apetalous without traces of petals in primordial stages; this condition is interpreted as an apomorphy. It is postulated that the development of a broad gynoecial nectary is responsible for the occurrence of an obdiplostemonous androecium. The gynoecium shows a number of anatomical particularities not observed in other Saxifragaceae. The presence and distribution of colleters is discussed.     

Regenerating Peripheral Axons Transport and Release Low-Molecular-Mass Materials In Vitro

Abstract: The release of radiolabeled material from regenerating frog sciatic nerves was studied using a multicom- partment chamber, in which the ganglia and the outgrowth region, respectively, were separated from the rest of the nerve. The nerves were incubated with radioactive amino acids in the ganglionic compartment, and the material transported to and released at the outgrowth region was collected and analyzed. Approximately 10% of the transported radioactivity was released over a 24-h incubation period. Of the released materials, 84% had a molecular mass of < 1,000 daltons [the low-molecular-mass (LM) fraction] as determined by exclusion chromatography. The presence of LM material could not be explained by leakage, nor was it due to intracellular or extracellular degradation of radiolabeled, transported proteins. It was reduced by cold and was shown by the use of vinblastine to be dependent on axonal transport. According to TLC, both the original precursor and metabolites thereof could be detected among the released LM material. The present results demonstrate the existence of a transport system for LM material in peripheral axons. The preferential release of LM over high-molecular-mass material at the outgrowth region suggests that it could serve specific functions during regeneration.     

Synthesis and pharmacology of the enantiomers of UH301: Opposing interactions with 5-HT1A receptors

The (S)-enantiomer of 5-fluoro-8-hydroxy-2-(dipropylamino) tetralin [(S)- 2a; (S)-UH301] was the first reported 5-HT_1A receptor antagonist. We now give a full account on the synthetic effort leading to the preparation of the racemate and the enantiomers of 2a. The crystal and molecular structure of 2a · HBr has been determined by X-ray diffraction and the absolute configuration has been deduced using statistical tests of the crystallographic R values. The unit cell is tetragonal (P4₁2₁2) with a = b = 13.2235 (2), c = 39.560(1) Å and contains two crystallographically independent molecules in each asymmetric unit. The two solid state conformers differ in the conformation of the N-propyl groups. The pharmacological characterization of the enantiomers was done by use of in vivo biochemical and behavioural assays in rats. The (R)-enantiomer of 2a is a 5-HT_1A receptor agonist of low potency while (S)- 2a does not exhibit any agonist properties at 5-HT_1A receptors. As a consequence of the opposing effects of the enantiomers, the racemate, rac- 2a, does not produce any clear-cut effects in rats. The reduced efficacy of (S)- 2a as compared to the well known 5-HT_1A receptor agonist 8-hydroxy-2-(dipropylamino)tetralin ( 1; 8-OH-DPAT) may be due to the fluoro-substituent induced negative potential of the aromatic ring. Chirality 8:531–544, 1996. © 1997 Wiley-Liss, Inc.     

The role of nectar sources for oviposition decisions of the common blue butterfly Polyommatus icarus

Neural limitations on information processing have been shown to play an important role for host plant specialization in herbivorous insects. The necessity of fast and accurate decisions favors the adoption of a few high-contrast signals, which selects against the use of multiple resources. Many species face a similar problem when searching for adult food sources and the simultaneous need to fulfill both search tasks can lead to a potential conflict. Some insects use the same host plant species for both adult and larval nutrition, which makes it possible to decrease the number of search images and thus potentially increase efficiency of the choices. The aim of this study was to investigate if there is a connection between choice of nectar sources and choice of oviposition host plant. In a laboratory experiment, females of Polyommatus icarus preferred to oviposit on Lotus corniculatus plants with flowers over those without flowers. Observations of behavioral sequences also revealed that oviposition often followed immediately after nectaring. The results suggest that nectar availability could play an important role in oviposition decisions of P. icarus and can provide one explanation to why some phytophagous insects not always choose the host plant that gives the best offspring performance.     

Hmi1p from Saccharomyces cerevisiae mitochondria is a structure-specific DNA helicase

Hmi1p is a Saccharomyces cerevisiae mitochondrial DNA helicase that is essential for the maintenance of functional mitochondrial DNA. Hmi1p belongs to the superfamily 1 of helicases and is a close homologue of bacterial PcrA and Rep helicases. We have overexpressed and purified recombinant Hmi1p from Escherichia coli and describe here the biochemical characteristics of its DNA helicase activities. Among nucleotide cofactors, the DNA unwinding by Hmi1p was found to occur efficiently only in the presence of ATP and dATP. Hmi1p could unwind only the DNA substrates with a 3'-single-stranded overhang. The length of the 3'-overhang needed for efficient targeting of the helicase to the substrate depended on the substrate structure. For substrates consisting of duplex DNA with a 3'-single-stranded DNA overhang, at least a 19-nt 3'-overhang was needed. In the case of forked substrates with both 3'- and 5'-overhangs, a 9-nt 3'-overhang was sufficient provided that the 5'-overhang was also 9 nt in length. In flap-structured substrates mimicking the chain displacement structures in DNA recombination process, only a 5-nt 3'-single-stranded DNA tail was required for efficient unwinding by Hmi1p. These data indicate that Hmi1p may be targeted to a specific 3'-flap structure, suggesting its possible role in DNA recombination.     

Reporter-linked monitoring of transgene expression in living cells using the ecdysone-inducible promoter system

Inducible promoter systems such as the ecdysone-inducible system or the tetracycline-regulated expression systems have proven to be powerful tools in studying gene function. In practice, such systems have met with the difficulty that either the vector expressing the transactivator gene or the vector carrying the response element are frequently silenced by flanking genomic sequences after stable integration. In order to identify those cells in a heterogeneous population in which a transgene is expressed from an ecdysone-inducible promoter, we have created the vector p2ER-EGFP/mcs that contains two ecdysone-inducible expression cassettes in tandem. Using two reporter genes, lacZ and green fluorescent protein (EGFP), we demonstrate that the expression of both genes can be co-induced from a very low baseline in CHO cells expressing the modified ecdysone receptor and the retinoid X receptor. The expression of EGFP and lacZ from vector p2ER-EGFP/lacZ follows the same Muristerone A concentration-dependence as that of EGFP from vector pER-EGFP, indicating that the juxtaposition of the two inducible promoters in vector p2ER-EGFP/mcs does not cause cross interference between them. We suggest that this modification of the ecdysone-inducible promoter system will allow for the visual control of the induced expression of other genes by Muristerone A.