The Fine Structure of Colpoda maupasi with Special Emphasis on Food Vacuoles*

SYNOPSIS. An electron microscope study of Colpoda maupasi Enriques, isolated from the intestine of the blue-tongued skink Tiliqua nigrolutea, showed that the fine structure of this ciliate is similar in all respects to that of free-living ciliates. The correspondence applies particularly to the structure, distribution and number of mitochondria. This organelle has a rich intramitochondrial structure in the form of microvilli; it is found close to the periphery, near the nuclear apparatus and in other parts of the cytoplasm. It was concluded that the association between Colpoda maupasi and Tiliqua nigrolutea was probably accidental and limited to the cyst stage. Thus electron microscopy confirmed a conclusion arrived at by light microscopy. The presence of numerous food vacuoles made it possible to study stages of digestion within this organelle. Four major types of food vacuole were distinguished. Type 1 food vacuoles are characterized by their large size, the presence of intact bacteria and abundance of water. In type 2 the food vacuole is deprived of water, the bacteria are pressed together and the nuclei have lost their structure. Type 3 food vacuoles contain only bacterial ghosts, cytoplasmic and nuclear material having been digested. Food vacuoles of this type are found only occasionally, suggesting their short duration. It is of interest that during this transient stage the bulk of digestion takes place. In type 4 nothing reminiscent of bacteria is found; there are only myelin figures and vesicles of different sizes. Evaginations and invagnations of the vacuolar membrane and vesicles of different size and structure inside and outside the food vacuoles of types 1, 3 and 4 suggest that extensive communication exists between the cytoplasm and the food vacuole. It seems likely that enzymes are delivered to the food vacuole and digested materials are released from the food vacuole to the cytoplasm.     

Ca-DEPENDENT CHANGES OF ACETYLCHOLINE RELEASE AND IP3 MASS IN TORPEDO CHOLINERGIC SYNAPTOSOMES

The aim of the present study was to investigate possible changes of inositol 1,4,5-trisphosphate (IP₃) mass in Torpedo cholinergic synaptosomes in conditions promoting stimulated acetylcholine (ACh) release. For this purpose, we used a radioreceptor IP₃ mass assay and a chemiluminescent method for ACh detection. Torpedo cholinergic synaptosomes have consistent IP₃ mass levels under resting conditions. The IP₃ mass was neither modified by changes in external Ca²⁺ nor by a Ca²⁺-free medium containing EGTA. IP₃ mass and ACh release, measured in the same conditions and in parallel, were increased by depolarization with high K⁺ and by the ionophores A-23187 and gramicidin-D in a manner dependent on external Ca²⁺ emphasizing that Ca²⁺ entry, independently of the influx mechanism involved, leads to an IP₃ increase. The phospholipase C_β inhibitors U-73122 and U-73343 reduced K⁺-stimulated IP₃ levels while K⁺-evoked ACh release was almost completely blocked suggesting an additional effect of these drugs on depolarization-neurotransmitter secretion coupling. The effect reported showing an increase of IP₃ by agents that stimulate ACh release may suggest a possible link between IP₃ metabolism and the neurotransmitter release mechanism. However, such a link is probably not a direct one as implied by the results obtained with the inhibitors of phospholipase C. Copyright © 1996 Elsevier Science Ltd     

Two new species of Galium (Rubiaceae) from the Iberian Peninsula

Two new species of the genus Galium are described from the Iberian Peninsula: G. moralesianum Ortega-Olivencia & Devesa, and G. talaveranum Ortega-Olivencia & Devesa. The first grows on limestone or dolomitic-limestone outcrops in south-east Spain (the Segura and Gádor mountain ranges) and shows morphological similarities with G. boissieranum Ehrend. & Krendl, which is endemic to southern Spain (mountains of Málaga). The second inhabits the margins of water courses, alder stands and cork-oak dehesas (parkland-type systems) of the west of the Iberian Peninsula, and is morphologically reminiscent of G. mollugo L. The chromosome numbers of these two species and of G. boissieranum are given.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 177−187.     

Encystment-Inducing Factor from Cultures of Acanthamoeba palestinensis

Acanthamoeba palestinensis grown in monolayer cultures encysted almost synchronously at a stationary phase, with a yield of about 80% cysts. Under these growth conditions an encystmentinducing factor was released into the medium by transforming amoebae. Cell-free supernatants induced encystment of amoebae from early-log phase cultures. The not dialyzable encystment factor was resistant to nuclease, protease and trypsin digestion, as well as to boiling, but the activity was almost completely destroyed by autoclaving. Isolation and further characterization of the factor will enable clarification of the mode of its action as a regulator of amoeba-cyst transformation.     

On seeds containing Eucommiidites troedssonii pollen from the Jurassic of Grojec, Poland

Together with other plant remains of Upper Liassic-Aalenian age there were found in Grojec near Krakow, Poland, seeds known from the Yorkshire Gristhorpe Bed as Allicospermum relemirum Harris. On maceration these seeds showed in their pollen chamber and mieropyle, pollen of Eucommiidites troedssonii Erdtman which adds to similar evidence provided already by Hughes (1961) and Brenner (1966).
The structure of the seed is described, discussed and compared with that of Spermatites pettensis Hughes which contained pollen of Eucommiidites delcourtii Hughes. S. pettensis is shown to agree in structure with the macerated A. retemirum , but it is of a different size. A. retemirum is considered to be related to either the Ginkgoales, Cycadales or Pteridosperms, or else to a new, not yet known group of plants. Its affinity with the Chlamydospermales is considered less likely.     

Growth, light interception and disease in field bean (Vicia faba): the effect of late infection by Ascochyta fabae

Growth and light interception were measured in field beans (Vicia faba) infected by Ascochyta fabae under field conditions. Despite late infection, disease reduced the leaf area index and the dry matter production of the crop. The main effect was due to a decrease of leaf area duration, which resulted in shorter duration of growth and lower final dry weights. The reduction in seed yield was significant, representing a decrease of 15% compared with a prophylactic fungicide treatment. The data are consistent with a small reduction in light use efficiency, but the observed differences were not significant during the period of crop growth.     

Evidence of Transcellular Strands in Transverse Cryostat Sections of Cucurbita pepo Sieve Tubes

Transverse cryostat sections of rapidly frozen vascular bundlesof Cucurbita pepo were viewed in a microscope with Nomarskioptics. Structural bodies were frequently observed in sievetube lumina and filling the sieve plate pores. The bodies consistof an outer boundary ring and an inner core, often granularin appearance, and may represent transverse sections of boundedtubes filled by substructural material. This evidence is consistentwith earlier observations of strand-like structures with parallelsubstructural elements seen in longitudinal sections.