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11.
According to current phylogenetic theory, both electroreceptors and electric organs evolved multiple times throughout the evolution of teleosts. Two basic types of electroreceptors have been described: ampullary and tuberous electroreceptors. Ampullary‐type electroreceptors appeared once in the common ancestor of the Siluriformes+Gymnotiformes (within the superorder Ostariophysi), and on two other occasions within the superorder Osteoglossomorpha: in the African Mormyriformes and in the African Notopteriformes. Tuberous receptors are assumed to have evolved three times; all within groups that already possessed ampullary receptors. With the exception of a single catfish species, for which studies are still lacking, all fish with tuberous electroreceptors also have an electric organ. Tuberous electroreceptors are found in the two unrelated electrogenic teleost lineages (orders Gymnotiformes and Mormyriformes) and in one non‐electrogenic South American catfish species (order Siluriformes). Electric organs evolved eight times independently among teleosts: five of them among the ostariophysans (once in the gymnotiform ancestor and in four siluriform lineages), once in the common ancestor of Mormyriformes, and in two uranoscopids. With the exception of two uranoscopid genera, for which no electroreceptive capabilities have been discovered so far, all electric organs evolved as an extension of a pre‐existing electroreceptive (ampullary) condition. It is suggested that plesiomorphic electric organ discharges (EODs) possessed a frequency spectrum that fully transgressed the tuning curve of ampullary receptors, i.e. a signal such as a long lasting monophasic pulse. Complex EOD waveforms appeared as a derived condition among electric fish. EODs are under constant evolutionary pressure to develop an ideal compromise between a function that enhances electrolocation and electrocommunication capabilities, and thereby ensures species identity through sexual and behavioural segregation, and minimizes the risk of predation. 相似文献
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Shigeko Ishimatsu Toshihiro Kawamoto Koji Matsuno Yasushi Kodama 《Biological trace element research》1995,49(1):43-52
In this study, eight kinds of nickel (Ni) compounds were orally administered to Wistar male rats and the distribution of each
compound was investigated 24 h after the administration. The Ni compounds used in this experiment were nickel metal [Ni−M],
nickel oxide (green) [NiO(G)], nickel oxide (black) [NiO(B)], nickel subsulfide [Ni3S2], nickel sulfide [NiS], nickel sulfate [NiSO4], nickel chloride [NiCl2], and nickel nitrate [Ni(NO3)2]. The solubilities of the nickel compounds in saline solution were in the following order; [Ni(NO3)2>NiCl2>NiSO4]≫[NiS>Ni3S2]>[NiO(B)>Ni−M>NiO(G)]. The Ni level in the visceral organs was higher in the rats given soluble Ni compounds; Ni(NO3)2, NiCl2, NiSO4, than that in the rats receiving other compounds. In the rats to which soluble Ni compounds were administered, 80–90% of
the recovered Ni amounts in the examined organs was detected in the kidneys. On the other hand, the Ni concentration in organs
administered scarcely soluble Ni compounds; NiO(B), NiO(G), and Ni−M were very low. The estimated absorbed fraction of each
Ni compounds was increased with the increase of the solubility. These results suggest that the kinetic behavior of Ni compounds
administered orally is closely related with the solubility of Ni compounds, and that the solubility of Ni compounds is one
of the important factors for determining the health effect of Ni compounds. 相似文献
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为了明确地枫皮的结构特征及其在石灰岩山顶和山腰疏林间两种环境下生长的叶片解剖结构的差异,本研究采用石蜡切片和半薄切片对地枫皮营养器官进行解剖观察并评价了叶片结构对不同生态环境的响应。结果表明:地枫皮根中次生维管组织发达,木射线和韧皮射线明显。老茎的次生构造中,皮层贮藏物质丰富,内有大的石细胞群,韧皮射线和木射线明显;而髓细胞内含有大量晶簇和少量单晶。在叶片横切面观上,叶为异面叶,表皮细胞一层,上表皮无气孔分布,主脉中薄壁细胞中分散有石细胞。叶片解剖结构显示,随海拔高度上升,地枫皮趋向于旱生植物的特点,其主要表现在叶片表皮细胞外壁角质层加厚,栅海比增加、海绵组织排列由紧密变疏松。另外,根皮、茎皮和叶肉中都分布有大量油细胞。 相似文献
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Phenolic Compounds and Antioxidant Activity of Different Organs of Potentilla fruticosa L. from Two Main Production Areas of China 下载免费PDF全文
This report compared the phenolic compounds and antioxidant activity of the leaves, flowers, and stems of Potentilla fruticosa L. collected from two main production areas of P. R. China (Taibai Mountains and the Qinghai Huzhu Northern Mountains). The results indicated that there were significant differences in the phenol contents and antioxidant activities among the different organs and between the two productions. High‐performance liquid‐chromatography analysis indicated that hyperoside, (+)‐catechin, ellagic acid, and rutin were the primary compounds in leaves and flowers; for stems, the content of six phenolic compounds, from two productions, were the lowest. The 1,1‐diphenyl‐2‐picryl hydrazyl (DPPH), 2,2‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) di‐ammonium salt (ABTS), ferric reducing power (FRAP), lipid peroxidation assays, and microbial test system (MTS) were used to evaluate the antioxidant activity. The results demonstrated that the leaves from two productions exhibited powerful antioxidant activity than other organs, which did not significantly differ from that of the positive control (rutin), followed by the flowers and stems. The correlation between the content of phytochemicals and the antioxidant activities of different organs showed that the total phenol, tannin, hyperoside, and (+)‐catechin contents may influence the antioxidant activity, and these compounds can be used as markers for the quality control of P. fruticosa. 相似文献
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In the last twenty-five years, young inflorescences, floral buds and individual floral organs of a number of species have been cultured in vitro. There is considerable variability in the requirement of plant growth regulators and nutritional factors for flower development of different species. This variability is compounded by the fact that the hormonal and nutritional requirements are different at various stages of organ and floral development. Experimental studies on normal and mutant flowers in vitro have provided insights into some of the regulatory processes in floral organogenesis. The potential use of the in vitro technique in elucidating the various mechanisms in flower development is stressed. 相似文献
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