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排序方式: 共有139条查询结果,搜索用时 31 毫秒
21.
中国东北典型森林生态系统植物叶片的非结构性碳水化合物研究 总被引:4,自引:0,他引:4
植物叶片的非结构性碳水化合物(NSC)不仅可以反应植物的碳供应状况,也能反应植物对外界环境的适应策略。利用传统的蒽酮比色法测定了东北3个典型森林生态系统(呼中、凉水和长白山)242种常见植物叶片的非结构碳水化合物,探讨了温带主要森林植物叶片NSC沿纬度梯度的变化趋势及其在物种-生活型-群落间的分布规律。实验结果表明:3个典型森林生态系统植物叶片可溶性糖、淀粉和NSC含量均呈偏正态分布,多数物种的含量偏中低水平;242种植物叶片可溶性糖、淀粉和NSC的平均含量分别为63.31、65.66和128.96 mg/g。在所调查的森林生态系统中,叶片可溶性糖、淀粉和NSC含量在不同生活型中表现各异。此外,乔木植物叶片的可溶性糖、淀粉和NSC含量从北到南呈递增趋势,呼中最低,凉水次之,长白山最高。乔木淀粉含量均表现为落叶树种大于常绿树种,可溶性糖和NSC含量变化趋势复杂。研究结果不仅为阐明东北主要森林生态系统植被碳代谢和生长适应对策提供数据基础,而且对理解植物对未来气候变化的响应机理提供数据支撑。 相似文献
22.
We conducted an 8-year exclosure experiment (1999–2006) in a forest–tundra ecotonal area in northwestern Finnish Lapland to
study the effects of reindeer grazing on vegetation in habitats of variable productivity and microhabitat structure. The experimental
sites included tundra heath, frost heath and riparian habitats, and the two latter habitats were characterized by hummock-hollow
ground forms. The total cover of vegetation, cover of willow (Salix spp.), dwarf birch (Betula nana), dwarf shrubs, forbs and grasses (Poaceae spp.) increased in exclosures in all habitats. The increase in the total cover of vegetation and in the covers of willow
and dwarf birch tended to be greatest in the least productive tundra heath. Opposing to the increase in the dominant vascular
plant groups, the cover and species number of bryophytes decreased in exclosures. We conclude that the effects of reindeer
grazing on vegetation composition depend on environmental heterogeneity and the responses vary among plant groups.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
23.
Porta M Zima AV Nani A Diaz-Sylvester PL Copello JA Ramos-Franco J Blatter LA Fill M 《Biophysical journal》2011,100(4):931-938
Caffeine (1, 3, 7-trimethylxanthine) is a widely used pharmacological agonist of the cardiac ryanodine receptor (RyR2) Ca(2+) release channel. It is also a well-known stimulant that can produce adverse side effects, including arrhythmias. Here, the action of caffeine on single RyR2 channels in bilayers and Ca(2+) sparks in permeabilized ventricular cardiomyocytes is defined. Single RyR2 caffeine activation depended on the free Ca(2+) level on both sides of the channel. Cytosolic Ca(2+) enhanced RyR2 caffeine affinity, whereas luminal Ca(2+) essentially scaled maximal caffeine activation. Caffeine activated single RyR2 channels in diastolic quasi-cell-like solutions (cytosolic MgATP, pCa 7) with an EC(50) of 9.0 ± 0.4 mM. Low-dose caffeine (0.15 mM) increased Ca(2+) spark frequency ~75% and single RyR2 opening frequency ~150%. This implies that not all spontaneous RyR2 openings during diastole are associated with Ca(2+) sparks. Assuming that only the longest openings evoke sparks, our data suggest that a spark may result only when a spontaneous single RyR2 opening lasts >6 ms. 相似文献
24.
Subtropical streams harbour higher genus richness and lower abundance of insects compared to boreal streams,but scale matters 下载免费PDF全文
25.
T Helaakoski L Pajunen K I Kivirikko T Pihlajaniemi 《The Journal of biological chemistry》1990,265(20):11413-11416
Mouse F9 teratocarcinoma stem cells differentiate in monolayer cultures in the presence of retinoic acid, dibutyryl cAMP, and isobutyl methylxanthine. This differentiation is associated with a marked increase in the synthesis rates and mRNA concentrations of basement membrane proteins such as type IV collagen. We report here that the differentiation also involves an increase of up to 50-fold in the concentrations of the mRNAs for the alpha and beta subunits of prolyl 4-hydroxylase, the enzyme required for the cotranslational and post-translational hydroxylation of proline residues in collagens. The time courses and magnitudes of increases in these two mRNA concentrations were similar to those observed in the same experiments for the mRNA of the alpha chain of type IV collagen. In the differentiated F9 cells the concentration of the alpha subunit mRNA was about 30% of the beta subunit mRNA concentration. Northern blot analyses indicated that the sizes of the alpha and beta subunit mRNAs in the differentiated mouse F9 cells are similar to those in human skin fibroblasts. The F9 cell differentiation system appears to provide a useful model for studies on the regulation of prolyl 4-hydroxylase synthesis. 相似文献
26.
Nani Van Gerven Sander E. Van der Verren Dirk M. Reiter Han Remaut 《Journal of molecular biology》2018,430(20):3657-3684
Amyloid fibrils are best known as a product of human and animal protein misfolding disorders, where amyloid formation is associated with cytotoxicity and disease. It is now evident that for some proteins, the amyloid state constitutes the native structure and serves a functional role. These functional amyloids are proving widespread in bacteria and fungi, fulfilling diverse functions as structural components in biofilms or spore coats, as toxins and surface-active fibers, as epigenetic material, peptide reservoirs or adhesins mediating binding to and internalization into host cells. In this review, we will focus on the role of functional amyloids in bacterial pathogenesis. The role of functional amyloids as virulence factor is diverse but mostly indirect. Nevertheless, functional amyloid pathways deserve consideration for the acute and long-term effects of the infectious disease process and may form valid antimicrobial targets. 相似文献
27.
In standard blind source separation, one tries to extract unknown source signals from their instantaneous linear mixtures by using a minimum of a priori information. We have recently shown that certain nonlinear extensions of principal component type neural algorithms can be successfully applied to this problem. In this paper, we show that a nonlinear PCA criterion can be minimized using least-squares approaches, leading to computationally efficient and fast converging algorithms. Several versions of this approach are developed and studied, some of which can be regarded as neural learning algorithms. A connection to the nonlinear PCA subspace rule is also shown. Experimental results are given, showing that the least-squares methods usually converge clearly faster than stochastic gradient algorithms in blind separation problems. 相似文献
28.
Annastasia Ediati Nani Maharani Agustini Utari 《Birth defects research. Part C, Embryo today : reviews》2016,108(4):380-383
Disorders of sex development (DSD) is a congenital condition in which the development of chromosomes, gonads, hormones, and reproductive structures are atypical. DSD brings with it a psychological impact on the affected individual and their families. The consensus statement on management of DSD strongly advised an integrated and multidisciplinary approach in providing care to the affected individuals. Studies have been conducted focusing on medical intervention, and more recently, there is increasing attention paid to psychological aspects of DSD. However, studies reporting cultural aspects of DSD are lacking. This review provides an overview on how culture impacts the affected individuals in coping with DSD and making decisions with regard to gender assignment or reassignment, help‐seeking behavior for medical treatments, attitudes toward medical treatment, religious beliefs, and values concerning marriage and fertility. The involvement of social scientists is needed to study sociocultural aspects of DSD from more diverse cultures, to help affected individuals and their families in gaining better social acceptance. Birth Defects Research (Part C) 108:380–383, 2016. © 2016 Wiley Periodicals, Inc. 相似文献
29.
30.
Inhibition of polyamine synthesis blocks urinary secretion of beta-glucuronidase from mouse kidney 总被引:1,自引:0,他引:1
The effect of inhibition of polyamine synthesis on castrated male mouse kidney beta-glucuronidase induction and secretion by testosterone was studied. Inhibition of the activities of polyamine synthesis key-enzymes, L-ornithine and S-adenosyl-L-methionine decarboxylases, was performed with the combined treatment of 2-difluoromethylornithine and methylglyoxal' bis(guanylhydrazone). Blockage of polyamine synthesis did not affect testosterone-induced increase in renal beta-glucuronidase but blocked its secretion into the urine. After withdrawal of inhibitor-treatment beta-glucuronidase secretion normalized, and repeated testosterone administration produced undisturbed beta-glucuronidase secretion peak in urine suggesting that blockage of beta-glucuronidase secretion was not due to the tissue damage produced by inhibitors. These results indicate that the stimulation of renal polyamine synthesis by testosterone is not necessary for the induction of beta-glucuronidase but is required for the urinary secretion of this protein. 相似文献