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1.
Evolution of epiphytes in Davalliaceae and related ferns   总被引:3,自引:0,他引:3  
The evolution of epiphytes in Davalliaceae was investigated by field observations and molecular phylogenetic analyses. Field studies revealed that in Davalliaceae and related ferns, epiphytes in a broad sense are classified into climber, secondary hemi-epiphyte, and obligate epiphyte, based on combinations of the places (ground vs. tree) of inferred spore germination and sporophyte growth. Some species of Davalliaceae have multiple life forms, i.e. secondary hemi-epiphyte and obligate epiphyte, whereas others are obligate epiphytes. Phylogenetic trees obtained from rbcL and accD gene sequences supported that secondary hemi-epiphytic Oleandra is sister to the epiphytic Davalliaceae and polygrammoid ferns. Analyses of life form evolution based on the phylogenetic relationships suggested that obligate epiphytes of the Davalliaceae and polygrammoid ferns evolved from secondary hemi-epiphytes, or less likely from climbers. We hypothesized a scenario for the evolution of life forms in Davalliaceae and related groups that involves successive changes in rhizome habit, root function, and germination place. Rhizome dorsiventrality and scale morphology, shared by climbers, secondary hemi-epiphytes, and obligate epiphytes examined, may be other innovations for the ferns to have evolved into epiphytes.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 495–510.  相似文献   
2.
ABSTRACT. Composition of rumen ciliate fauna in five Zambian, sassaby antelopes was determined. Six genera, 18 species, and four forms were identified. One new species and form, belonging to the subfamily Diplodiniinae, were found, then labeled Ostracodinium damaliscus n. sp. and Diplodinium bubalidis f. aspinosum n. f., respectively. Only ophryoscolecid species were present while isotrichids were absent. Twelve of 18 total species are commmonly found in African antelopes. Three of those 12 species, Entodinium fyferi, Enoploplastron garstangi and Opisthotrichum janus , are only found in African antelopes. Percentage composition was low in the genera ml of rumen fluid, and the average number of ciliate species per host was 17.2.  相似文献   
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Drought-affected plants experience more than just desiccationof their organs due to water deficit. Plants transpire 1000times more molecules of water than of CO2 fixed by photosynthesisin full sunlight. One effect of transpiration is to cool theleaves. Accordingly, drought brings about such multi-stressesas high temperatures, excess photoradiation and other factorsthat affect plant viability. Wild watermelon serves as a suitablemodel system to study drought responses of C3 plants, sincethis plant survives drought by maintaining its water contentwithout any wilting of leaves or desiccation even under severedrought conditions. Under drought conditions in the presenceof strong light, wild watermelon accumulates high concentrationsof citrulline, glutamate and arginine in its leaves. The accumulationof citrulline and arginine may be related to the induction ofDRIP-1, a homologue of ArgE in Escherichia coli, where it functionsto incorporate the carbon skeleton of glutamate into the ureacycle. Immunogold electron microscopy reveals the enzyme tobe confined exclusively to the cytosol. DRIP-1 is also inducedby treating wild watermelon with 150 mM NaCl, but is not inducedfollowing treatment with 100 µM abscisic acid. The salttreatment causes the accumulation of -aminobutyrate, glutamineand alanine, in addition to a smaller amount of citrulline.Citrulline may function as a potent hydroxyl radical scavenger.  相似文献   
6.
In 1997, we conducted a vegetation survey in three semi-arid natural grasslands (steppes) withdifferent livestock grazing intensities in Southwest Heilongjiang Province, China. The dominant grasslandspecies was the grass Stipa baicalensis Roshev. Grasslands with light, intermediate, and heavy grazingintensities were located 10, 5, and 2 km from a village, respectively. Villagers use the steppe to raise cattle,horses, sheep, and goats. Each of the three grasslands was surveyed by placing 100 quadrats (50 cm×50 cm)along a 50 m line transect. Each quadrat was divided into four equal areas (25 cm×25 cm; S-quadrats) and allplant species occurring in each of these smaller areas were identified and recorded. These data were summa-rized into frequency distributions and the percentage of S-quadrats containing a given species and thevariance of each species were estimated. The power law was applied to these estimates. The power law wasused to evaluate the spatial heterogeneity and frequency of occurrence for each species in the grasslandcommunity. The lightly grazed grassland exhibited high spatial heterogeneity (caused by large plant size),the highest species diversity, and a high occurrence of S. baicalensis. In contrast, the heavily grazedgrassland exhibited high spatial heterogeneity (caused by patchy populations of small plant size), lowspecies diversity, and a low occurrence of S. baicalensis. We judged that the heavily grazed grassland wasovergrazed and exclusion of livestock from the degraded areas is necessary for recovery.  相似文献   
7.
杜仲叶林枝木醋液化学成分及抑菌活性研究   总被引:2,自引:0,他引:2  
以杜仲叶林枝木为原料,采用干馏法,分90℃~200℃、200℃~340℃和340℃~520℃共3个温度段收集杜仲叶林枝木粗木醋液,经过静置、活性炭粉吸附焦油处理等过程得到精制木醋液,然后对所得木醋液的理化性质和抑菌活性进行了研究,并对抑菌活性最强的木醋液的化学成分进行了GC/MS分析。结果表明:(1)杜仲叶林枝木醋液产生的温度范围为90℃~520℃,其中200℃~340℃段产量最大、pH值最低、有机酸含量最高、抑菌能力也最强。(2)GC/MS分析表明,温度段为200℃~340℃的木醋液中约含有42种化合物,主要为酚类、酸类、酮类和醛类等,其中酚类化合物含量最高,占总量的46.81%,其次为有机酸类物质。初步分析确定木醋液抑菌活性成分为酚类物质。  相似文献   
8.
Important regulatory controls of melanogenesis that operate at the subcellular level to modulate the structural and/or the functional nature of the melanins and melanin granules produced in melanocytes are reviewed. Melanocyte stimulating hormone and agouti signal protein have antagonistic roles and possibly opposing mechanisms of action in the melanocyte. In the mouse, melanocyte stimulating hormone promotes melanogenic enzyme function and elicits increases in the amount of eumelanins produced, while agouti signal protein reduces total melanin production and elicits the synthesis of pheomelanin rather than eumelanin. We are now beginning to understand the complex controls involved in regulating this switch at the molecular and biochemical levels. The quality and quantity of melanins produced by melanocytes have important physiological consequences for melanocyte function and undoubtedly play important roles in the various functions of the melanins per se, including hair and skin coloration and photoprotection.  相似文献   
9.
In 1997, we conducted a vegetation survey in three semi-arid natural grasslands (steppes) with different livestock grazing intensities in Southwest Heilongjiang Province, China, The dominant grassland species was the grass Stipa baicalensis Roshev. Grasslands with light, intermediate, and heavy grazing intensities were located 10, 5, and 2 km from a village, respectively. Villagers use the steppe to raise cattle, horses, sheep, and goats. Each of the three grasslands was surveyed by placing 100 quadrats (50 cm×50 cm) along a 50 m line transect. Each quadrat was divided into four equal areas (25 cm×25 cm; S-quadrats) and all plant species occurring in each of these smaller areas were identified and recorded. These data were summarized into frequency distributions and the percentage of S-quadrats containing a given species and the variance of each species were estimated. The power law was applied to these estimates. The power law was used to evaluate the spatial heterogeneity and frequency of occurrence for each species in the grassland community. The lightly grazed grassland exhibited high spatial heterogeneity (caused by large plant size), the highest species diversity, and a high occurrence of S. baicalensis. In contrast, the heavily grazed grassland exhibited high spatial heterogeneity (caused by patchy populations of small plant size), low species diversity, and a low occurrence of S. baicalensis. We judged that the heavily grazed grassland was overgrazed and exclusion of livestock from the degraded areas is necessary for recovery.  相似文献   
10.
The expression of various melanogenic proteins, including tyrosinase, the tyrosinase-related proteins 1 (TRP1) and 2 (TRP2/DOPAchrome tautomerase), and the silver protein in human melanocytes was studied in six different human melanoma cell lines and compared to a mouse derived melanoma cell line. Analysis of the expression of tyrosinase, TRP1, TRP2, and the silver protein using flow cytometry revealed that in general there was a positive correlation between melanin formation and the expression of those melanogenic enzymes. Although several of the melanoma cell lines possessed significant activities of TRP2, the levels of DOPAchrome tautomerase in extracts of human cells were relatively low compared to those in murine melanocytes. Melanins derived from melanotic murine JB/MS cells, from melanotic human Ihara cells and HM-IY cells, from sepia melanin, and from C57BL/6 mouse hair were chemically analyzed. JB/MS cells, as well as Ihara cells and HM-TY cells, possessed significant amounts of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) derived melanins, this being dependent on the activity of TRP2. Kinetic HPLC assays showed that 5,6-dihydroxyindole (DHI) produced during melanogenesis was metabolized quickly to melanin in pigmented KHm-1/4 cells, whereas DHI was stable in amelanotic human SK-MEL-24 cells. A melanogenic inhibitor that has been purified from SK-MEL-24 cells that suppressed oxidation of DHI in the presence or absence of tyrosinase, but had no effect on DHICA oxidation. The sum of these results suggest that the expression of melanogenic enzymes as well as the activity of a melanogenic inhibitor are critical to the production of melanin synthesis in humans.  相似文献   
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