Ultrastructure of the acanthella of Paratenuisentis ambiguus (Acanthocephala)
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Syncytium
Primordium
Epidermis (zoology)
Far-red light and long photoperiods promote flowering in Arabidopsis. We report here that when 30-day-old vegetative plants were induced with a continuous light treatment enriched in far-red light, flowers developed directly from previously initiated primordia. Specifically, plants induced with our continuous incandescent-enriched (CI) treatment produced an average of two primary-axis nodes with a leaf/flower phenotype, indicating that approximately two leaf/paraclade primordia per plant produced an individual flower from tissue that typically would differentiate into a paraclade (secondary inflorescence). Assays for APETALA1::β-glucuronidase activity during the CI photoinduction treatment indicated that the floral meristem identity gene APETALA1 was transcriptionally activated in primordia with a leaf/paraclade bias and in primordia committed to leaf/paraclade development. APETALA1::β-glucuronidase activity levels were initially highest in young primordia but were not correlated strictly with primordium fate. These results indicate that primordium fate can be modified after primordium initiation and that developing primordia respond quantitatively to floral induction signals.
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The epidermis of four species of Didymorchis ('Turbellaria', Temnocephalida) was studied using silver nitrate staining and electron microscopy. The epidermis is composed of 12-14 syncytia separated by lateral membranes. The organisation of the epidermal mosaic is almost identical for all species studied. Neighbouring syncytia (or groups of syncytia) differ in the presence (or absence) and density of locomotory cilia, in the structure of the cytoplasm, and in the abundance and nature of the gland ducts that penetrate them. The dorsal syncytia differ from the ventral ones in the form of the electron-dense inclusions in the modified mitochondria present throughout the epidermis. Multisyncytial organisation of the epidermis supports the placement of Didymorchis in the Temnocephalida rather than in the Dalyellioida. Three other features of the epidermis are apomorphies of Didymorchis. Presence of borders between syncytia with the same structure cannot be explained on a functional basis. We suggest that it represents a relatively primitive stage in the evolution of the multisyncytial epidermis. In this regard Didymorchis is different from more specialised temnocephalids (e.g. Diceratocephala) in which the separation of syncytia (with one exception) reflects functional differences between syncytia.
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Turbellaria
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Primordium
Epidermis (zoology)
Basal (medicine)
Polarity (international relations)
Root hair
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It was found that S shape curves could describe leaf, bracteal and spikelet primordium differentiation in relation to GDD. The Logistic equations of the three types of S curves were all highly significant with R 2 greater than 0.74. The apex primordium differentiation exhibited similar patterns to winter and spring type varieties on main stem and tillers, but marked differences among different sowing dates. The thermalchrons of apex primordium differentiation were reduced greatly in the order of leaf. bracteal and spikelet, and thus the rates of apex primordium differentiation were accelerated with plant development progress. Measured with GDD, differences between different sowing dates for the end of bracteal primordium differentiation and beginning of spikelet primordium differentiation were much greater than for the beginning of bracteal primordium differentiation, indicating that impact of phasic development was primary on spikelet primordium initiation in wheat. Bracteal primordium number ( x ) was significantly correlated with spikelet number ( y ) in the two types of varieties, as well as in main stems and tillers, with an integrated single equation as y =1.812+0.897 x .
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Main stem
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Abstract During their different life stages, parasites undergo remarkable morphological, physiological, and behavioral “metamorphoses” to meet the needs of their changing habitats. This is even true for ectoparasites, such as the monogeneans, which typically have a free-swimming larval stage (oncomiracidium) that seeks out and attaches to the external surfaces of fish where they mature. Before any obvious changes occur, there are ultrastructural differences in the oncomiracidium’s outer surface that prepare it for a parasitic existence. The present findings suggest a distinct variation in timing of the switch from oncomiracidia epidermis to the syncytial structure of the adult tegument and so, to date, there are three such categories within the Monogenea: (1) Nuclei of both ciliated cells and interciliary cytoplasm are shed from the surface layer and the epidermis becomes a syncytial layer during the later stages of embryogenesis; (2) nuclei of both ciliated cells and interciliary syncytium remain distinct and the switch occurs later after the oncomiracidia hatch (as in the present study); and (3) the nuclei remain distinct in the ciliated epidermis but those of the interciliary epidermis are lost during embryonic development. Here we describe how the epidermis of the oncomiracidium of Discocotyle sagittata is differentiated into two regions, a ciliated cell layer and an interciliary, syncytial cytoplasm, both of which are nucleated. The interciliary syncytium extends in-between and underneath the ciliated cells and sometimes covers part of their apical surfaces, possibly the start of their shedding process. The presence of membranous whorls and pyknotic nuclei over the surface are indicative of membrane turnover suggesting that the switch in epidermis morphology is already initiated at this stage. The body tegument and associated putative sensory receptors of subadult and adult D. sagittata are similar to those in other monogeneans.
Viral tegument
Syncytium
Epidermis (zoology)
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In two guinea pigs (five years old, neutered male, and two and a half months old male, respectively) suffering from interstitial pneumonia, multinucleated giant cells were observed histologically in lungs, spleen and liver. The giant cells showed intranuclear, pale basophilic inclusions. Adenovirus could be demonstrated by electron microscopy.The multinucleated cells are supposed to be of histiocytic origin, since they contained variable amounts of haemosiderin in their cytoplasm. Formation of histiocyte-derived syncytia as a result of virus-induced cell fusion is discussed.
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Basophilic
Multinucleate
Foreign-body giant cell
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In the fern Osmunda cinnamomea, leaf primorida may be excised and grown in sterile culture before or subsequent to their irreversible determination as leaves. It has been demonstrated that P 3 primordia (third-oldest primordia) are not irreversibly determined as leaves at the time of excision for they exhibit a tendency to develop as shoots rather than leaves when cultured aseptically. When grown singly they become shoots 75.0% of the time; when grown in physiological contact as paired units they exhibit a tendency to become shoots at approximately the same level. The hypothesis that the active site of leaf determination is through the direct or indirect control of the shoot apical meristem is questioned and an alternative hypothesis is proposed which suggests that a morphogenetic factor is formed in older primordia which will diffuse to younger primordia to influence younger primordia to develop as leaves rather than shoots. The latter hypothesis is supported by experiments in which P 3 primordia grown in physiological contact (as pairs) with P 10 or P 12 primordia produce more than twice as many leaves as unpaired or paired P 3 primordia.
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Multinucleate
Syncytium
Cell fusion
Langhans giant cell
Foreign-body giant cell
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Syncytium
Trophoblast
Cell fusion
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