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The effects of cytochalasin B on the development and morphology of the Micrasterias cell vary according to different developmental stages. CB (especially 5–6 μm/ml) does not stop the growth of a developing semicell during early developmental stages and allows the formation of a three–lobed form, which is a kind of a basic form preceding the actual morphogenesis, further growth and development still being totally prevented by the same concentration. This is due to the occurrence of two separate cytoplasmic streaming systems in the developing semicell, one being cortical, more CB sensitive, the other being more central, not as sensitive to CB, both being microfilament based. The cortical streaming system supports tip growth, and many observations indicate that this system is also associated with the intermediation of the nuclear control regulating morphogenesis in Micrasterias. The effects of CB are specific: it has not been found to have distinct effects on the ultrastructure of the cell, on cell wall material production, or on the turgor pressure of the cell.  相似文献   

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Abstract. The division rate of Micrasterias torreyi cells grown under continuous illumination first accelerated but soon slowed down, and the cells lost their ability to divide after about 1 month. During the treatment the cells became pale green, the pyrenoids became fewer in number and defects appeared in the chloroplasts. After 1 month, the cells also soon died, even when subjected to intermittent illumination. The most striking structural alterations were found in the chloroplasts: the starch granules lost their typical structure, the lamellae were damaged and numerous electron dense precipitates appeared in the chloroplasts. The precipitates were similar to those formed in cells treated with supraoptimal external calcium concentrations and X-ray microanalysis showed that the precipitates were rich in calcium in both cases. The results suggest that light controls and activates the Ca2+ uptake in the plasma membrane as well as in the chloroplast envelope, that the large sized chloroplasts of Micrasterias are effective in regulation of cytoplasmic Ca2+ concentration, and that the injuries caused by continuous illumination may be largely due to the accumulation of Ca2+ in the chloroplasts.  相似文献   

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This paper reports a diatom assemblage found by the author from the Upper Tertiary continental strata in Shangdu County in Niemongol Autonomous Region and Dunhua County in Jilin Province of China. The diatom assemblage in Shangdu County comprises 4 new species and 2 new varieties: Tetracyclus ellipticus var. ovalifolium Li; Tetracyclus ellipticus var. rostrata Li; Tetracyclus jaoi Li; Tetracyclus navicularis Li; Tetracyclus shangduensis Li and Tetracyclus sinensis Li. From the Miocene of Dunhua County; JilinProvince are recorded 2 new species: Tetracyclus dunhuanensis Li and Tetracyclus ovaliformis Li.  相似文献   

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B. Oertel  E. Jelke 《Protoplasma》1986,135(2-3):173-179
Summary Zoospore formation in sporangia ofPhytophthora infestans, the causal agent of potatoes downy mildew disease, was influenced by reduction of oxygen tension, by application of a respiratory poison (KCN), and by an inhibitor of cytokinesis (cytochalasine B). As demonstrated by different methods of light microscopy, in all three cases the percentage of morphologically abnormal, multinucleate, multiflagellate cells increased. High concentrations of KCN caused a complete inhibition of zoospore formation. These effects are interpreted as disorders of the process of cytokinesis during zoosporogenesis.  相似文献   

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? Premise of the study: The goal of this study was to illuminate the evolutionary history and ecological importance of plant mixotrophy-the uptake and utilization of exogenous organic compounds. ? Methods: We quantitatively assessed the effect of sugar amendments on laboratory growth of Sphagnum compactum as a representative emergent peat moss and two species of ecologically associated zygnematalean algae, Cylindrocystis brebissonii and Mougeotia sp. ? Key results: Together with observations published elsewhere, our results suggest that under carbon or light limitation, the uptake of exogenous sugars by cells of charophycean algae and peat mosses may help these organisms maintain positive carbon balance. Utilization of 1% glucose by aquatic-grown algae helped to relieve dissolved inorganic carbon limitation, enhancing photoautotrophic growth by factors of 9.0 and 1.7, respectively. After an 8-wk growth period, amendments of 1% and 2% glucose enhanced air-grown moss biomass by 28 and 39 times, respectively, that of controls lacking sugar amendments. After 9 wk, 1% fructose enhanced biomass by 21 times, and 2% sucrose enhanced biomass by 31 times. ? Conclusion: Our results indicate that plant mixotrophy is an early-evolved trait. The results also indicate that quantitative differences in sugar utilization by bryophytes and charophycean algae correlate with relative investments in protective cell-wall polyphenolics measured in previous studies, suggesting that sugar utilization may subsidize the cost of producing phenolic wall compounds in bryophytes.  相似文献   

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Under nitrogen deficiency the unicellular chlorococcalean green alga, Eremosphaera viridis De Bary, was able to synthesize secondary carotenoids (SC). Nine SC were identified as six astaxanthin esters, echinenone, canthaxanthin and a lutein ester, previously not described in green algae under nitrogen deficiency. These SC, jS-carotene and the main part of lutein were located in lipid bodies outside the chloroplasts in the cytosol. The synthesis of SC could be inhibited by the herbicides norflurazon and nicotine. This result supported the idea that SC in cells ot Eremosphaera viridis were synthesized de novo rather than derived from primary carotenoids.  相似文献   

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J Zhang  S Wang  H Li  B Hu  X Yang  Z Wang 《PloS one》2012,7(7):e41657
The diffuse coevolution between two moth species (Epicephala lativalvaris and E. mirivalvata) and two plant species (Breynia fruticosa and B. rostrata) is reported based on field observations and indoor experiments conducted in Hainan and Fujian, China. Study results showed that the two Epicephala species jointly pollinated the two Breynia species, which led to a unique obligate pollination mutualism of two-to-two species specificity. A single Epicephala larva exclusively fed on seeds of host plants and developed to maturity by consuming all six seeds of each fruit, whereas a fraction of intact fruits were left to ensure the reproduction of plants within the whole population. Larvae of the two Epicephala species are competitive for resources; the population of E. mirivalvata is much smaller than that of E. lativalvaris, which has resulted from the differences in the female ovipositor structures and oviposition mode. The life history of Epicephala species highly coincides with the phenology of Breynia plants, and different phenology of B. fruticosa resulted in the different life history of the two Epicephala species in Hainan and Fujian. The natural hybridization of two host plants, possibly induced by the alternate pollination of two Epicephala species, is briefly discussed.  相似文献   

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S ummary : The influence of the age and activity of bacteria, their concentration in the protective medium, the pH value of the medium, the temperature of thawing, and the time of storage on the survival of L. leichmannii during freezing and thawing has been investigated.  相似文献   

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本文记述了蜡蚧一新种:贵州克里蜡蚧Kilifia guizhouensis sp.n.。模式标本保存于贵州农学院植保系。该种是克里蜡蚧属在中国记录的第二种。它与本属的其它种可由下面检索表区分。 克里蜡蚧属分种检索表1.背孔(dorsalpore)在背面中央形成一纵带,在背侧面正对后足基节的上方各形成一横带………K.diversipes(Cockerell) 背孔在背面既不形成纵带、也不形成横带。…………………………………………………………………………………………… 22(1)肛板(anal plate)前侧边与后侧边之比为2.2—2.7………………………………………………K.americana Ben—Dov. 肛板前侧边与后侧边之比为1.4-2.1……………………………………………………………………………………………………33(2)至少4%的缘毛(marginal setae)顶端不分枝…………………………………………………………………………………4 除2—3根位于肛裂边(each side of anal cleft)的缘毛处.所有缘毛顶端均分枝………………………………………54(3)至少80%的缘毛顶端分枝.其分枝长……………………………………………………贵州克里蜡蚧K.guizhouensi sp.nov. 最多50%的缘毛顶端分枝、其分枝短…………………………………………………………………………  相似文献   

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两种髭蟾的Ag—NORs,C—带及核型的研究   总被引:2,自引:0,他引:2  
李树深  费梁 《遗传学报》1990,17(3):211-215
本文叙述和比较了峨眉髭蟾和哀牢髭蟾的核型,C-带和Ag-NORs,结果表明两者有下列相同方面:2n=26(6+7)、除No.3为SM外,其余诸对概为M,次缢痕和Ag-NoRs位于6q,并都表现出异形现象,No.1长臂有长度异形,但所增染色体片断不呈现C-带正染,C-带正染主要是在各对染色体的着丝点区域,另外No.2短臂近着丝区域亦为正染。这些表明二者之间有很大的核带型同源性。但是二者间在核型的某些对应染色体之间,在相对长度(6对)和臂比值(2对)方面有显著性差异,故可推测其机制是相互易位和臂间倒位。另外,哀牢髭蟾未发现与性别相关的异形性染色体。  相似文献   

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《Journal of Asia》1999,2(2):97-103
This paper describes two new species of the Anthribidae from Korea, Euparius koreanus n. sp. and Uncifer angulatus n. sp. Two other species, Eucorynus crassicornis (Fabricius) and Habrissus analis Morimoto are new to the fauna of Korea. Their important features are illustrated. The genera, Uncifer, Eucorynus, and Habrissus are newly recognized from Korea.  相似文献   

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For an examination of the progression of cavitation in large-diameter earlywood vessels of a deciduous ring-porous tree, potted saplings of Fraxinus mandshurica var japonica Maxim. were frozen and then thawed. The changes in the amount and distribution of water in the lumina of the current year's earlywood vessels during the course of the freezing and thawing were visualized by cryo-scanning electron microscopy. When samples were frozen, most of the current year's earlywood vessels were filled with water. After the subsequent thawing, the percentage of cavitated current-year earlywood vessels gradually increased with time. All of the current year's earlywood vessels were cavitated within 24 h, and only limited amounts of water remained in the lumina of earlywood vessels. Similar cavitation of earlywood vessels was observed after thawing of frozen, excised stem pieces. In contrast, many vessels of the current year's latewood retained water in the lumina during freezing and thawing. These observations indicate that the cavitation of the current year's earlywood vessels is not produced during freezing but progresses during rewarming after freezing in F. mandshurica var japonica.  相似文献   

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记述采自辽宁、河南、山东、浙江等省的小腹茧蜂属Microgaster Latreille2新种和1中国新记录种;刻胸小腹茧蜂Microgaster punctithorax,sp.nov.、玉主螟小茧蜂Microgaster ostriniae,sp.nov.和平原小腹茧蜂Microgaster campestris Tobias1964,new record。模式标本保存在浙江大河保护系昆虫标本  相似文献   

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Filaments ofPhymatodocis nordstedtiana Wolle were isolated from a sample of a Texan lake. Cultures were established and examined by light and scanning electron (SEM) as well as transmission electron microscopy (TEM). It is shown that the pores apparent on light microscopical examination are not of the cosmaroid type as expected. TEM examination disclosed that they are similar to those found in the generaClosterium Ralfs andPenium Bréb. Furthermore, it could be demonstrated by light and SEM microscopy that the primary cell wall is shed during cell division. The remaining secondary cell wall of the mature cell consists of interwoven bands of parallel microfibrils. A conspicuous overlap of the semicell walls clearly denotes the isthmus region. The significance of these deviations unusual for desmids is discussed. Suggestions are made that the taxonomic position ofPh. nordstedtiana should be re-evaluated.  相似文献   

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We determined the fruit predators and seed dispersers of two species of durian ( Durio , Bombacaceae), D. graveolens and D. zibethinus , which have contrasting aril color and timing of dehiscence by observing fruiting trees in Deramakot forest reserve. In our observations in the wild, both species were extensively predated by orangutans before fruits matured. Durio graveolens was dispersed by black hornbills and D. zibethinus was dispersed by long-tailed macaques.  相似文献   

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A model is presented of the regulation of ethylene biosynthesis in relation to submergence and flooding resistance. It is based on time-course measurements of ethylene production, ethylene accumulation, and concentrations of free and conjugated 1-aminocyclo-propane-1-carboxylic acid (ACC) in submerged and drained flooding-resistant Rumex palustris Sm. and flooding-sensitive Rumex acetosella L. plants. From these data, in vivo reaction rates of the final steps in the ethylene biosynthetic pathway were calculated. According to our model, submergence stimulates ACC formation and inhibits conversion of ACC to ethylene in both Rumex species, and as a result, ACC accumulates. This may explain the stimulated ACC conjugation observed in submerged plants. Although submergence inhibited ethylene production, physical entrapment increased endogenous ethylene concentrations in both flooding-resistant R. palustris and flooding-sensitive R. acetosella plants. However, R. palustris plants controlled their internal ethylene levels in the long term by a negative regulation of ACC synthase induced by ethylene. In flooding-sensitive R. acetosella plants, absence of negative regulation increased internal ethylene levels to more than 20 [mu]L L-1 after 6 d of submergence. This may accelerate the process of senescence and contribute to their low level of flooding resistance.  相似文献   

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