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2.
A germination study was carried out on seeds of Clinopodium sandalioticum (Bacch. & Brullo) Bacch. & Brullo ex Peruzzi & Conti (Lamiaceae), a wild aromatic plant endemic to Sardinia. Seeds were incubated at a range of constant (5–25°C) and an alternating temperatures regime (25/10°C), with 12 hours of irradiance per day. The results achieved at 10°C were also compared with those obtained after a period of cold stratification at 5°C for three months. Final seed germination ranged from ca. 28% (5°C) to ca. 72% (25/10°C). A base temperature for germination (Tb) of ca. 5°C and a thermal constant for 50% germination (S) of 89.3°Cd were identified and an optimal temperature for germination (To) was estimated to be comprised between 20 and 25°C. Cold stratification negatively affected seed viability and germination at 10°C. Although a typical “Mediterranean germination syndrome”, could not be detected for C. sandalioticum seeds, these results were coherent with those previously reported for other Mediterranean Lamiaceae species.  相似文献   
3.
In this paper we discuss and demonstrate the importance of several factors relative to the relationship between time and evolution of biosequences. In both quantitative and qualitative measurements of the genetic distances, the compositional constraints of the nucleotide sequences play a very important role. We demonstrate that when homologous sequences significantly differ in base composition we get erratic branching order and/or wrong evaluation of the evolutionary rates. We must consider that every gene may have a different evolutionary dynamic along its sequence, generally linked to its functional constraints; this too can seriously affect its clocklike behavior. We report some cases showing how these factors can affect the quantitative measurements of the genetic distances of biosequences. Presented at the NATO Advanced Research Workshop onGenome Organization and Evolution, Spetsai, Greece, 16–22 September 1992  相似文献   
4.
  • Morphological and functional seed traits have important roles in characterising the species regeneration niche and help to understand the reproductive biology of rare and threatened plants, which can thus support appropriate plant conservation measures.
  • Seed morphometric and dispersal kinetics of the critically endangered Dioscorea strydomiana were measured and compared with those of four other Dioscorea species, and seed germination response under constant temperatures (5–35 °C) was compared with that of the congeneric and widespread D. sylvatica.
  • Seed mass of D. strydomiana (ca. 14 mg) was twice that of D. sylvatica, but similar to or smaller than the other species examined. Seeds of D. strydomiana have the lowest speed of descent and lowest variability in most of the morphological traits considered, suggesting lower phenotypic plasticity but higher variance in the wing‐loading value. Seeds of D. strydomiana reached maximum germination at 15 °C (ca. 47%), which decreased slightly to ca. 37% at 25 °C and was completely inhibited at 35 °C. D. sylvatica seeds started to germinate at 10 °C (ca. 3%), reached 75–80% germination at 15–20 °C and maximum (ca. 90%) at 25–30 °C. Base temperatures for germination (Tb) were 9.3 and 5.7 °C, for D. strydomiana and D. sylvatica, respectively. Due to the higher germination percentages of D. sylvatica, ceiling and optimum temperatures could also be modelled for this species, suggesting higher sensitivity to high temperature for seeds of D. strydomiana.
  • The detected poor seed lot quality of D. strydomiana suggests difficulties in reproduction from seed, highlighting the need for further investigation and conservation actions for this threatened yam species.
  相似文献   
5.
Cation export from Alaskan arctic watersheds   总被引:1,自引:1,他引:0  
The concentrations and stream fluxes of Na, K, Ca and Mg were determined in 1978, 1980 and 1981 in the Toolik Lake watershed and in 1978 in the upper Kuparuk River watershed. The annual export of K was strongly influenced by high K concentrations at the initiation of spring melt. Potassium concentrations were positively correlated with concentrations of particulate and dissolved organic carbon, particulate and dissolved phosphorus, and particulate, dissolved organic and ammonium nitrogen, suggesting a common origin in the decomposition of tundra plants. Calcium and Mg stream concentrations were generally highest in July and August when the depth of the soil active layer reached a maximum of ∼ 0.5 m. Precipitation-derived Na and K accounted for up to half of the Na and K stream export while chemical weathering supplied > 85 % of exported Ca and Mg. Cation export rates in these arctic foothill watersheds are among the lowest recorded.  相似文献   
6.
Rises in intracellular calcium cause several events of physiological significance, including the regulated release of neuronal transmitters. In this study, the effects of divalent cations on the structural organization of cytomatrix in presynaptic terminals was examined. [35S]Methionine-radiolabeled guinea pig retinal ganglion cell cytomatrix proteins were axonally transported [in slow component b (SCb) of axonal transport] to the neuron terminals in the superior colliculus. When the peak of radiolabeled cytomatrix proteins reached the terminals, synaptosomes containing the radiolabeled cytomatrix proteins were prepared. Approximately 40% of each SCb protein was soluble after hypoosmotic lysis of the radiolabeled synaptosomes in the presence of divalent cation chelators. Lysis of synaptosomes in the presence of calcium ions over a range of concentrations, however, caused a dramatic decrease in solubility of the presynaptic SCb proteins. The cytoplasmic effects may result from a calcium-dependent condensation of cytoplasm around presynaptic terminal membrane systems. There are two major presynaptic SCb proteins (at 60 and 35 kDa), that exhibited exceptional behavior: they remained as soluble in the presence of calcium as under control conditions, suggesting that they were relatively unaffected by the mechanism causing the decrease in SCb protein solubility. Also examined were the effects of other alkaline earth and transition metal divalent cations on the presynaptic SCb proteins.  相似文献   
7.
This study focused on understanding the termite traveling behavior. Artificial tunnels with different curvatures and base surface roughness were constructed. Each tunnel was 50 mm in length, with widths of W (W = 2, 3, or 4 mm). The distance between the two ends of the tunnel was D (D = 20, 30, 40, or 50 mm). A higher value of D means a lower curvature. The roughness, R (R = 60, 120, 240 and ∞), was generated by uniformly sanding the substrate with a sanding machine. A higher R value means a finer base surface. The symbol ∞ represents a smooth surface. Time (τ) taken by a termite to pass through the tunnel was measured. τ was longer in tunnels with a smooth surface compared with the tunnels with a rough surface. When W = 2, there was no effect of the roughness on speed. This is because the narrow tunnel width diluted the effects of the smoothness of the surface. When W = 3, τ was statistically shorter for R = 240, than for R = 60 and 120. This suggests that an appropriate surface roughness could positively contribute to the traveling speed.  相似文献   
8.
Acidic deposition, nutrient leaching and forest growth   总被引:9,自引:0,他引:9  
Studies in Germany and confirmed in North America established that the forest decline that developed in the late 1970's and 80's resulted from a deficiency in one or more of the nutrient cations: Ca2+, Mg2+, and K+. These nutrients are essential to the structure of the foliage, to photosynthesis and to the growth of the trees. The reactions and mechanisms involved in the entry of nutrients to the soil, their storage, and rate of transfer to the soil solution, and through it, to the fine roots and to the leaves at the top of the tree are reviewed. The continuing material balance studies carried out on a watershed at the Hubbard Brook Experimental Forest in New Hampshire allow a unique analysis of the changes caused in these nutrient transfers by acid rain. The nutrient cations are stored in the soil by adsorption on negatively charged clay, and the presence of an acid is required for their release to the soil solution. In pre-industrial times this acid was H2CO3, which was subsequently displaced from the soil solution by H2SO4 and HNO3, as a result of acid deposition. The effect of the increased concentration of the negatively charged SO4 2– and NO3 anions seeping through the soil, compared with that of the HCO3 that had been previously present, resulted in a substantially increased rate of transfer of an equivalent of Ca2+ and other positively charged nutrient cations from the soil to the soil solution. The increased concentration of Ca2+ in the soil solution resulted in both an initial increase in the rate of biomass growth and in a simultaneous increase in the rate of Ca2+ loss in the effluent soil solution from the watershed. It was found that this increased rate of removal of Ca2+ from the watershed soil had become greater than its rate of input to the soil from weathering and from dust and rain. As a result, the large Ca2+ inventory that had built up in the soil as a result of the reduced leaching in the years prior to the entry of acid rain, that started in about the1880's, was eventually depleted in the hardwood forest at Hubbard Brook in the 1980's, about 100 years later. With insufficient Ca2+ available for its continuing transfer, net biomass growth on the watershed stopped. This resulted from the rate of tree mortality becoming equal to that of the small incremental growth of a few trees on the watershed. The future growth of forests is at risk from the long-term effects of acid deposition. The fundamental nature of the reactions involved indicates that similar growth anomalies are occurring in other forests impacted by acid rain. These changes from normal biomass growth can affect the amount of CO2 stored in the biomass, of importance to our understanding of Global Warming.  相似文献   
9.
目的:定量毛细管电泳法因采用了定量阀进样的方式,其进样量为固定值,定量结果更加可靠,且重复性好。本文探讨了采用定量毛细管电泳方法测定市售虫草类保健品中虫草素、腺嘌呤、尿嘧啶、腺苷、尿苷含量的可行性,优化了分析条件,并对其进行含量测定。方法:以浓度为40 mM、pH 9.5的硼砂为缓冲液,工作电压为-15 kv,采用定量毛细管电泳的方测定了虫草类制品中的核苷及碱基类物质的含量。结果:五种核苷及碱基类物质在优化的定量毛细管电泳条件下得到了良好的分离和定量结果,峰面积RSD值小于1.4%,测定了其在虫草菌丝体粉末及虫草王胶囊中的含量。结论:首次利用定量毛细管电泳法对虫草类保健品中的虫草素、腺嘌呤、尿嘧啶、腺苷、尿苷的含量进行了定量测定,不同形式虫草类保健品中核苷、碱基的种类和含量有差异。该方法快速、准确,对虫草类保健品的质量控制有重要意义。  相似文献   
10.
We report here the synthesis, characterization and kinetic studies of cis-[RuCl2(cyclen)]+ in aqueous solution, where cyclen is the macrocyclic ligand 1,4,7,10-tetraazacyclododecane. The complex releases one Cl producing cis-[RuCl(OH)(cyclen)]+ in aqueous solution at pH 4.60. The product of this reaction was characterized by Ultraviolet-Visible (UV-Vis) spectrum in comparison to the synthesized cis-[RuCl(OH)(cyclen)](BF4)·2H2O. The electrochemical data showed that Epc of the Ru(III/II) peak increases as the macrocycle ring size decreases and also when the trans conformation is changed to cis. The chloride affinity of Ru(III) depends on the macrocycle ring size since cis-[RuCl2(cyclam)]+ (cyclam=1,4,8,11-tetraazacyclotetradecane) does not release chloride for at least 12 h. The overall effect between cyclam and cyclen reflects the fact that the electron involved in the reduction enters a nonbonding π-d orbital and its energy is affected by the macrocyclic ligand.  相似文献   
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