Ultrastructure of Carposporogenesis in the Red Alga Caulacanthus ustulatus (Gigartinales, Caulacanthaceae)

Carposporangium differentiation in Caulacanthus ustulatus (Turner)Ktzing proceeds through four developmental stages. The youngestcarposporangia are embedded within confluent mucilage and containa nucleus, a few small starch granules, concentric membranebodies and proplastids without a peripheral thylakoid. The intermediate-agedcarposporangia are characterized by the formation of fibrousvacuoles by a fibrous vacuole associated organelle (FVAO). Plastidsalso start to develop their internal thylakoid system. In nearlymature carposporangia, highly active, curved dictyosomes producecored vesicles, while fibrous vacuoles increase in number anddisplay a perinuclear arrangement. Abundant starch granulesare present, some of which exhibit a degenerating appearance.A carposporangium wall is formed and plastids complete theirinternal thylakoid system. Carposporangium maturation is signalledby the presence of adhesive vesicles. Fully developed and peripherallyarranged plastids, centrally located fibrous vacuoles, fewerstarch granules and a monolayered wall are the features of maturecarposporangia. Carposporogenesis, Caulacanthus ustulatus (Turner) Kützing, red algae, ultrastructure     

Host range, purification and some properties of rubus Chinese seed-borne virus

A previously undescribed virus, for which the name rubus Chinese seed-borne virus (RCSV) is proposed, was isolated from a single, symptomless plant of an unidentified Rubus species grown from seed collected in the wild in the People's Republic of China, Experimentally RCSV infected 23 out of 39 spp. in six out of eight families. The virus was seed-transmitted in Chenopodium quinoa (100%) and Nicotiana bigelowii (27%). RCSV was not transmitted by the nematodes Xiphinema diversicaudatum or X. index. The particles of RCSV were isometric, c. 30 nm in diameter with some penetrated by negative stains. In thin sections particles were found in double walled tubular structures with an outer membrane enclosing one or more tubules. In crude extracts some particles were found within single-walled tubules. Two virus-associated bands were seen in sucrose density gradients of purified preparations. The upper band was not infective and consisted of penetrated particles apparently devoid of nucleic acid. The lower, infective band was resolved into two components, of density 1.452 and 1.461 g/ml, in caesium chloride isopycnic gradients. There were two polypeptides (mol. wts c. 47 000 and 25 200 daltons) and two nucleic acid species (one of mol. wt c. 1.4 × 10⁶ daltons; the second was poorly defined by the methods used but was of higher molecular weight). RCSV was distantly related serologically (6–7 SDI) to the type isolate of strawberry latent ringspot virus (SLRV) and also reacted with antisera to serologicaly distinct grape and olive isolates of SLRV. It did not react with antisera to 10 other isometric viruses.     

Reduced Polyteny of Ribosomal RNA Cistrons in Giant Chromosomes of <Emphasis Type="Italic">Drosophila hydei</Emphasis><Superscript>*</Superscript>

The polytenization of rRNA cistrons in Drosophila species is studied in an attempt to follow the course of under-representation of heterochromatic compared with euchromatic chromosome regions.     

Variation in pea aphid population development in three different habitats

Abstract.

• 1 Seasonal population growth rates for the pea aphid, Acyrthosiphon pisum Harris, were determined in three different host plant habitats; alfalfa, Medicago sativa (L.), clover, Trifolium pratense (L.), and peas, Pisum sativum (L.); over four years and eight places. It was possible to estimate a common intrinsic rate of increase for each host plant habitat.
• 2 An analysis of the relative influence of temporal, spatial and host plant habitat variation showed that the host plant habitat was most important in determining the growth rates of the populations, both in rate of build-up and decline.
• 3 Patterns of alate production in the three different habitats differed substantially between the annual peas and the two perennial legumes. During the summer, alate production was large and rapid in peas and remained low and constant in clover and alfalfa
• 4 Parasitism was highest in peas. The species composition of parasitoids differed between crops.
• 5 Aphids in annual peas had a higher intrinsic rate of increase and a faster rate of decline than in the two perennial legumes. This explains the presence of both migratory and sedentary forms among pea aphids.

     

Endocrine Correlates of Seasonal Body Mass Dynamics in the Collared Lemming (Dicrostonyx groenlandicus)

Many winter-active temperate rodent species show seasonal, photoperiod-mediatedchanges in body mass that correlate with changes in food availability,gaining mass when food is abundant. The collared lemming (Dicrostonyxgroenlandicus), an arctic species, also undergoes a seasonaltransition in body mass, but one that is temporally out of phasewith that observed in species from lower latitudes; whereastemperate species increase in mass when exposed to relativelylong day lengths, collared lemmings do so under long but decreasingday lengths. This adaptation may be in response tothe timingof peak above-ground biomass in the arctic. Validation of thishypothesis requires a more thorough examination of both collaredlemmings and other arctic species. In the collared lemming, photoperiod-mediated changes in bodymass are correlated with changes in serum concentrations ofprolactin, thyroid hormones, corticosterone, and growth hormone,and pineal concentrations of melatonin. These observations arecompared to those obtained with temperate small mammals, andpossible cause-and-effect relationships between body mass andhormonal parameters are discussed.     

Nutritional suitability of some uni-algal diets for freshwater calanoids: unexpected inadequacies of commonly used edible greens and others

• 1 Naupliar and copepodid development times (Dn and Dc, respectively) of two African freshwater calanoids (Metadiaptomus meridianus and Tropodiaptomus spectabilis) were measured on mono-specific diets of comparably sized Chlamydomonas reinhardii, Scenedesmus acutus, Cryptomonas sp., Rhodomonas minuta, Cyclotella meneghiniana, and Selenastrum capricornutum, to test the nutritional adequacy of these algae. Comparisons were made at a standard temperature (17°C) and food supply level (1 mgCl^?1).
• 2 All diets other than Scenedesmus and Selenastrum supported complete naupliar development at broadly comparable times within and between calanoids, apart from greatly protracted Dn values for M. meridianus on Cyclotella. Dc durations were more variable between diet types, and both Chlamydomonas and Cyclotella were inferior or inadequate for copepodid development.
• 3 Both naupliar and copepodid stages ingested radiolabelled Scenedesmus and Selenastrum readily. Comparative incorporation rate measures of Selenastrum and Cryptomonas respectively exceeded estimated metabolic maintenance needs of stage 3/4 nauplii of T. spectabilis by some 56% and 790%. Scope for growth (‘surplus’ energy) was accordingly fourteen-fold greater on Cryptomonas than on Selenastrum /Scenedesmus. The dietary inadequacy of these two green algae is thus attributed largely to low digestibility, and perhaps some biochemical deficiency.

     

Common Epitopes In the Circumsporozoite Proteins of Plasmodium Berghei and Plasmodium Gallinaceum Identified By Monoclonal Antibodies to the P. Gallinaceum Circumsporozoite Protein

ABSTRACT. Monoclonal antibodies that react with the circumsporozoite protein of the avian malaria Plasmodium gallinaceum sporozoites also reacted with circumsporozoite protein of the rodent malaria Plasmodium berghei. Two types of reactivity were identified: 1) two monoclonal antibodies reacted with P. berghei sporozoite protein by enzyme-linked immunosorbent assay, Western blot and indirect immunofluorescence antibody, 2) six other monoclonal antibodies reacted with P. berghei sporozoites by ELISA and Western blot only. We studied whether these differences could be explained by reactivity in enzyme-linked immunosorbent assay with different P. berghei circumsporozoite peptides. Although all P. gallinaceum monoclonal antibodies reacted with the P. berghei repeats, the first group reacted with a conserved peptide sequence, N1, whereas the second group did not. These results suggest that circumsporozoite proteins from P. gallinaceum and P. berghei share common epitopes. the biological significance of our finding is not yet clear. Indeed, the cross-reactive monoclonal antibodies giving a positive indirect immunofluorescence antibody with the P. berghei sporozoites only caused a borderline effect on the living P. berghei parasites in vitro as measured by inhibition of sporozoite infectivity.     

Stonefly predation along a hydraulic gradient: a field test of the harsh—benign hypothesis

SUMMARY. 1. Microhabitat preferences of predatory stoneflies and four prey taxa were assessed by taking benthic samples along a hydraulic gradient in a Black Forest stream in West Germany. Densities of predator and prey species were estimated at twenty-one hydraulic regimes.
2. Enclosures containing the stonefly, Dinocras cephalotes , and control cages with no predators were placed in the substrate at hydraulic regimes favourable and unfavourable to predators. Cages received initial prey communities that were obtained from benthic samples taken at hydraulic regimes matching those intended for each cage.
3. Population densities of the two most numerically important prey taxa, the mayfly. Baetis rhodani , and the Chironomidae, were reduced in the presence of Dinocras , but only when enclosures were placed in the hydraulic regimes favourable to the predator. Thus, predation effects increased as the hydraulic regime became more benign to the predators.
4. Densities of two other prey species rare in the diets of Dinocras ( Hydropsyche instabilis and Gammarus fossarum ) were generally unaffected by predators regardless of the hydraulic regime.
5. These data provide support for the hypothesis that perception of the abiotic regime as harsh or benign to predators is a good predictor of predator impact on densities of preferred prey species. In harsher abiotic regimes, impact will be low, while impact will be high in benign abiotic regimes.