Concanavalin A-Induced Morphological Changes and Its Binding Sites in Starfish Follicle Cells as Revealed by Electron Microscopy

Concanavalin A (Con A) stimulates the production in starfish follicle cells of 1-methyladenine, a hormone which induces oocyte maturation. We have therefore investigated Con A-induced morphological changes and Con A-binding sites in the follicle cell using native Con A and horseradish peroxidase- or ferritin-labeled Con A (HRP-Con A, Fer-Con A). After isolated follicle cells were incubated with Con A (1 mg/ml), vacuoles, the Golgi complex and multivesicular body-like organelles (MVBs) became prominent in most of the cells. After follicle cells were prefixed and then incubated with Fer-Con A for 60 min, tagged ferritin was diffusely and randomly distributed as single or small clustered particles on the cell surface. The incubation of isolated follicle cells with Fer-Con A for 10 min before fixation resulted in numerous ferritin particles localized along the internalized membrane, and also in vacuoles, MVBs and small lysosome-like structures. After 60 min incubation with Fer-Con A, ferritin was further located in large lysosome-like structures and in vesicles near and in the Golgi area as well as in the organelles described above. HRP-Con A binding sites were also observed in vacuoles and MVBs of the intact cells.
These results suggest that Con A binds at first to the cell surface and causes rapid internalization and that membrane-bound Con A is easily endocytosed into vacuoles, MVBs and lysosome-like structures, and is later incorporated in some vesicles in the Golgi area.     

Effect of Crown Asymmetry on Size-Structure Dynamics of Plant Populations

The effect of crown asymmetry on the size–structure dynamicsof populations was evaluated using a spatial competition modelincorporating crown asymmetry. Computer simulations were carriedout with various combinations of density levels, spatial patterns,and degrees of asymmetry in competition to assess how they modifythe effect of crown asymmetry on size–structure dynamics. In the model, crown asymmetry is expressed by the crown-vector,or the vector linking the stem base and the centre of the projectedarea of the crown on the horizontal plane. Crown-vectors areassumed to develop in the manner by which crowns repel eachother. As crown-vectors develop, the positions of the crown-centresmove. Competition between individuals is expressed by a neighbourhoodmodel, in which individual growth is determined by the distancefrom, and size of, the neighbours' crown-centres. Generally, populations of individuals which developed asymmetriccrowns had larger survivorship, larger mean size, smaller coefficientsof variation and skewness, and a more regular spatial patternthan populations of individuals which developed symmetric crowns.The effect of crown symmetry is generally stronger in populationswith high density and a clumped spatial pattern. The effectof mortality caused by one-sided competition on size-structuredynamics was similar to that of crown asymmetry; mortality increasedmean size, reduced size hierarchy, and made the spatial patternmore regular. Because mortality was heavier in populations withoutcrown asymmetry, its effect on size-structure dynamics cancelledout, or overwhelmed, the effect of crown asymmetry in latergrowth stages. If crown asymmetry is associated with a reductionin growth, the effect of crown asymmetry is reduced. Nevertheless,the resultant population structure is different from that ofpopulations without crown asymmetry. Competition; crown asymmetry; morphological plasticity; neighbourhood interference model; size-structure dynamics     

Changes in Activities of Glucose Metabolising Enzymes in Germ Cells during Spermatogenesis in Rats

The rate of ¹⁴CO₂, liberation from [¹⁴C-1]glucose was identical to that from [¹⁴C-6]glucose in spermatids, but more than the latter in spermatogonia. Rotenone (1 μM) completely inhibited ¹⁴CO₂ release from [¹⁴C-1]glucose in spermatids, but decreased it only 30% in spermatogonia. The activity of glucose-6-phosphate dehydrogenase, but not 6-phosphogluconate dehydrogenase, was markedly lower in spermatocytes and spermatids than in spermatogonia. The activities of the glycolytic enzymes, glucosephosphate isomerase, fructose diphosphatase, glyceraldehyde-3-phosphate dehydrogenase and enolase, differed only slightly in spermatids and spermatogonia. It is concluded that the low glucose-6-phosphate dehydrogenase activity may contribute to the low activity of the pentose cycle in spermatocytes and spermatids.     

Diel rhythmicity of prey-search activity and its predominance over starvation in the lady beetle, Coccinella septempunctata bruckii

ABSTRACT. The locomotor activity of the lady beetle, Coccinella septempunctata bruckii Mulsant (Coleoptera: Coccinellidae), was recorded during food deprivation in LD 16:8 h and continuous light. Activity was relatively low immediately after the lady beetle was fed to satiation but increased from 4 to 24 h later. It thereafter gradually decreased to a low level when the food was withheld for several days. Over a period of 10 days of starvation the beetles showed a high level of activity throughout the photophase and a low level during the scotophase in LD 16:8 h. In continuous light this rhythmic pattern persisted, with a free-running period of c. 22 h, significantly shorter than 24 h. The results suggest that the endogenous circadian timing predominates over 'hunger' as a determinant of search activity. The lady beetle accepted and consumed aphid prey presented at night, but the number of prey consumed was significantly lower than in the light. This suggests that, during the dark, activity related to prey-searching is suppressed, though lady beetles are able to accept and consume prey even at night.     

NEURAL COMPETENCE AND CELL LINEAGE OF GASTRULA ECTODERM OF NEWT EMBRYO

The change in the capacity to form neural structures was quantitatively analyzed in both intact and isolated ectoderms of Cynops pyrrhogaster gastrula. The frequency of explants with induced neural structures abruptly decreases between stage 12c and stage 13b in intact ectoderm, and between 12 hr and 18 hr preculture in isolated ectoderm. The quantitative analysis also made clear that the size of the cell population of induced neural structures was gradually reduced with the aging of the ectoderm. The authors simultaneously examined the cell proliferation of early gastrula ectoderm and confirmed that all ectodermal cells divided at least once within 18 hr at 23°C, after which the neural competence of the ectoderm completely disappeared.
The relationships between neural competence and cell lineage (cell generation) of the ectoderm are discussed in the light of these findings.