Reproducibility of vegetation cover estimates in south‐central Alaska forests

Abstract. Reproducibility of vegetation measurements is critical for large‐scale or long‐term studies, where numerous observers collect data, but past studies have questioned repro‐ducibility of some techniques. Five methods of evaluating understory composition were appraised for reproducibility among six observers in two forest types in south‐central Alaska: ocular estimates in quadrats, overall community species rank and cover estimates, nested rooted frequency, horizontal‐vertical profiles, and pin drop (systematic points). One forest type was selected to represent structure of coastal communities, another to represent structure of interior Alaska communities. Three general methods of evaluating reproducibility were considered: standard deviations (precision among observers), components of variance (percentage of total variance attributable to observers), and analysis of variance (significance of observer variance). Observer variances were generally similar among techniques and significant in most cases. No technique stood out as being more reproducible than others. Features of techniques other than reproducibility may be more important when selecting a technique. Management decisions based on vegetation cover data should consider the observer errors involved as well as biological significance.     

Photoacclimation of Dunaliella tertiolecta (Chlorophyceae) Under Fluctuating Irradiance

We investigated photoacclimation of Dunaliella tertiolecta (Butcher) in irradiance (I) regimes simulating mixed layer conditions of turbid estuarine waters or lakes. D. tertiolecta was exposed to a range of fixed I regimes to establish baseline physiology-I relationships that were compared with subsequent photoacclimation to a simulated mixed layer. Measured indices of photoacclimation included cellular pigmentation, chlorophyll variable fluorescence, and effective photosystem 2 antenna size. While D. tertiolecta grown under fluctuating I maintained division rates comparable to cells grown at high I, the cells exhibited characteristics of photoacclimation consistent with cells grown under a stable regimes at irradiances considerably lower than the average I of the simulated mixed layer.     

《动物学》课程教学探讨

动物学是生物科学专业重要的专业基础课。结合自身教学实践,对动物学在专业课程体系和学生知识体系中地位进行再认识,并就该课程教学内容的构成、主要线索,教学过程,以及如何在教学过程中结合人文素质教育,拓宽学生视野,提高学生综合素质进行探讨。     

《发酵工程与设备》课程设计教学的研究

《发酵工程与设备》课程设计是重要的实践教学环节, 在实践教学中起到承上启下的作用, 可为学生毕业后到工厂工作打下良好的工作基础。对课程设计所处地位以及教学观念、内容、方法等教学各环节进行交流探讨。     

棉铃虫核多角体病毒p10基因的序列及转录分析

为了利用棉铃虫核多角体病毒（HaSNPV）p10基因的启动子构建重组病毒杀虫剂及表达系统,应用末端测序法和引物步移法测定了p10基因的序列,并应用Northern杂交和引物延伸实验对该基因进行了深入的转录特性分析,HaSNPV p10基因被定位于基因组DNA的115.4kb-115.6kb处,转录方向与多角体基因相反,在其上下游分别发现了p26和p74基因。转录分析结果确定了p10基因是个极晚期基因,其转录从杆状病毒晚期转录保守序列GTAAG的第二个A开始,转录产物大小约为430nt。HaSNPV p10基因最早可检测到的转录是在病毒感染后的20h,随后其转录产物量迅速放大,到感染后72h达到非常高的水平。围康时相分析同时还检测到一个大小为1300nt的产物,推测该产物为p26和p10通读的转录产物。对HaSNPV P10蛋白序列的分析表明,该蛋白第6－44位及第51－65位氨基酸序列处含多个典型的卷曲螺旋七聚体重复结构,两片段间相隔6个氨基酸残基,在该蛋白序列的第20－34位与第51－65位存在L－X（2）－L－X（10）－L的亮氨酸重复。Helical net分析表明,HaSNPV P10的疏水氨式酸分布为两个集簇区,两者互为180度转角。     

Time Course of the Metabolite Patterns of Intraventricularly Injected [3H]Noradrenaline in Rat Brain Regions

In the hypothalamus, septum, pons with medulla, and hippocampus regions of rat brain, the level of radioactivity of [3H]noradrenaline and of five of its metabolites were determined up to 6 h after intraventricular injection of the tritiated amine. The following main results were found: In anterior hypothalamus and septum, the [3H]noradrenaline level declined in two phases. Similar turnover curves were obtained for the primary deaminated metabolites, with almost the same final half-lives as for [3H]noradrenaline. The level of the initial methylation product, normetanephrine, also showed a biphasic decline, which did not correspond to that of [3H]noradrenaline but rather was faster throughout the experiment. The final metabolites (i.e., the glycol sulfates) reached maximal levels in hypothalamus and septum earlier than in other regions. Thereafter, their levels declined with almost similar rates in all areas tested, but always faster than the [3H]noradrenaline level. The following conclusions were drawn: In areas rich in catecholaminergic nerve terminals, there seems to be a site, in addition to the vesicular storage pool, that accumulates exogenous noradrenaline and then releases it with relatively short half-lives. The contents of primary deaminated metabolites followed the turnover of [3H]noradrenaline at both sites. Exogenous [3H]noradrenaline seems to be methylated at two extraneuronal sites, which are distinguished by the rates of subsequent deamination. The size of the pool of slowly deaminated [3H]normetanephrine that is formed immediately after [3H]noradrenaline injection determined the apparent turnover of this product throughout the experiment and, thus, like the final metabolites, reflects for several hours the initial degradation of the unstored [3H]noradrenaline, rather than the metabolism of the stored amine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estimation of the Temporal Course of Evoked Secretion of Transmitter Quanta in the Frog Neuromuscular Junction

In experiments on the cutaneothoracic muscle of the frog, we recorded, using the technique of two-electrode voltage clamp at a normal Ca²⁺ concentration (1.8 mM), multiquantum end-plate currents (EPC) and miniature uniquantum EPC (mEPC). Multiquantum signals, when compared with uniquantum currents, were characterized by longer leading and trailing edges. The quantum composition of multiquantum signals estimated according to the ratios of EPC and mEPC amplitudes was, on average, 27% lower than that calculated according to the ratios of their integral values (areas). These data demonstrate that stimulus-evoked transmitter secretion from the motor nerve endings is noticeably asynchronous. Based on the parameters of the experimental EPC and mEPC, we estimated the temporal course of evoked secretion using various techniques: spectral analysis, a system of linear equations, and Van der Kloot's method. Using convolution with uniquantum signals, we found that spectral analysis is the best technique for such estimation. Calculated parameters of the temporal course of secretion were the following: risetime 0.20 msec and decay time constant 0.33 msec. The respective distribution significantly differed from that of the synaptic delays of extracellularly recorded uniquantum EPC by longer durations (150-200%) of the leading and trailing edges. We hypothesize that these differences are related to the geometry of the junction and the temporal sequence of switching on of the active zones in the nerve ending upon their activation by spreading action potentials. Factors influencing the temporal course of evoked secretion of the transmitter in the junction under study (its asynchronicity, in particular) are discussed.     

Industrial Ecosystems as Food Webs

Colocated industries exchange products and by-products in ways reminiscent of the exchange of resources in biological ecosystems. To better understand these "industrial ecosys-tems", we have applied food-web theory to a set of 19 actual and hypothetical eco-industrial parks and integrated biosys-tems. We find a linear relationship between number of industrial tenants and number of linkages among them and connectance values of 0.5 to 0.6 (typical of biological ecosystems). The results may provide initial perspective on designing eco-industrial parks to maximize the utilization of resources and minimize the generation of wastes. Increased connectance in industrial ecosystems, however, does not necessarily imply increased stability or improved environmental performance.     

The causes of altered chlorophyll fluorescence quenching induction in the Arabidopsis mutant lacking all minor antenna complexes

Non-photochemical quenching (NPQ) of chlorophyll fluorescence is the process by which excess light energy is harmlessly dissipated within the photosynthetic membrane. The fastest component of NPQ, known as energy-dependent quenching (qE), occurs within minutes, but the site and mechanism of qE remain of great debate. Here, the chlorophyll fluorescence of Arabidopsis thaliana wild type (WT) plants was compared to mutants lacking all minor antenna complexes (NoM). Upon illumination, NoM exhibits altered chlorophyll fluorescence quenching induction (i.e. from the dark-adapted state) characterised by three different stages: (i) a fast quenching component, (ii) transient fluorescence recovery and (iii) a second quenching component. The initial fast quenching component originates in light harvesting complex II (LHCII) trimers and is dependent upon PsbS and the formation of a proton gradient across the thylakoid membrane (ΔpH). Transient fluorescence recovery is likely to occur in both WT and NoM plants, but it cannot be overcome in NoM due to impaired ΔpH formation and a reduced zeaxanthin synthesis rate. Moreover, an enhanced fluorescence emission peak at ~679?nm in NoM plants indicates detachment of LHCII trimers from the bulk antenna system, which could also contribute to the transient fluorescence recovery. Finally, the second quenching component is triggered by both ΔpH and PsbS and enhanced by zeaxanthin synthesis. This study indicates that minor antenna complexes are not essential for qE, but reveals their importance in electron stransport, ΔpH formation and zeaxanthin synthesis.