The compatibility of osmotica in cyanobacteria

Abstract. The solutes accumulated by cyanobacteria in response to hyper-osmotic stress include Na⁺, K⁺, sucrose, trehalose, glucosyl-glycerol, glyeine betaine and glutamate betaine. The compatibility of several of these solutes with glutamine synthetase activity has been examined using cell-free extracts from a range of freshwater, marine and halotolerant cyanobacteria. All of the solutes tested were compatible with (i.e. non-inhibitory to) enzymic activity at physiological concentrations and the results demonstrate a rank order of compatibility which correlates with the concentrations at which the organic solutes occur in cyanobacteria, i.e. glycine betaine > polyol-derivatives > disaccharides and with the upper salinity limit for growth. The protection against inhibition by NaCl (halo-protection) afforded by these solutes to enzymic activity was also examined. Only glycine betaine was found to exert a significant halo-protective effect and this may be explained by differences in the mechanism of compatible solute function between small charged molecules and sugars/polyols.     

Genetic control of colour /pattern polymorphism in British populations of the spittlebug Philaenus sputnarius (L.) (Homoptera: Aphrophoridae)

The results of breeding experiments designed to determine the genetic control of the colour/pattern polymorphism in Philaenus spumarius in certain British populations are described and contrasted to previously published results for material taken from populations in southern Finland. The 11 principal phenotypes are controlled by seven alleles at a single autosomal locus, with complex patterns of dominance and co-dominance. In Finland, and most of the rest of the species' extensive range, the eight melanic morphs are wholly or substantially limited to the females, in which they are dominant to the typical form. Previously, this sex limitation has been explained in terms of reduced penetrance of melanic alleles in males and/or dominance reversal between the sexes, such that the eight melanic phenotypes (controlled by five alleles which are adjacent in the dominance heirarchy) are dominant to typical in the females but recessive in the males. Published data on morph frequencies in S Finland and on breeding experiments using material collected from these populations are re-examined and it is shown that neither theory accounts adequately for all the evidence. By contrast, in most British populations there is greatly increased penetrance in males of the melanic morphs which are strictly female-limited elsewhere. Breeding experiments, using P. spumarius taken from selected British populations, provide clear evidence that melanics are dominant to typical in both sexes. This difference in genetic control is entirely consistent with the balance of morph frequencies between the sexes in the populations from which the breeding material for the two separate studies was taken. Experimental material for this study was taken from populations in the Cynon Valley in south Wales, which have the highest melanic frequencies in the species' range and show particularly clear expression of melanic phenotypes in males. Both of these features are strongly correlated with severe aerial pollution from a local smokeless fuel factory. Selection for melanism in these populations is clearly strong, which probably accounts for the high level of penetrance and the dominance of melanics to typical in both sexes. Although further experiments are needed, it is suggested that regulatory loci, controlling the penetrance and expression of melanic alleles in males, could account for the observed differences in genetic control between populations in Britain and Finland.     

Plasmodium Sporozoite Interactions with Macrophages In Vitro: a Videomicroscopic Analysis

ABSTRACT. Studies of in vitro interactions between Plasmodium berghei sporozoites and peritoneal macrophages from mice and rats were performed. A videomicroscopic analysis was made of interactions observed by phase-contrast microscopy. Our results showed a diversity of dynamic interactions between sporozoites and macrophages that included no interaction, surface interaction without sporozoite interiorization, active sporozoite penetration, active penetration with subsequent sporozoite escape, macrophage destruction, and the formation of "tethers" or web-like structures by sporozoites that had actively invaded macrophages. Sporozoites are thus clearly capable of actively invading host macrophages and are not restricted to being phagocytosed for interiorization. The formation of "tethers" by the moving sporozoite might function in vivo by anchoring the sporozoite to the cells lining the lumen of the liver sinusoid. Active sporozoite motility appears to be a functional phenomenon involved in sporozoite invasion of host liver cells.     

The Occurrence of Nitrate Reduction in the Leaves of Woody Plants

Nitrate reductase activities greater than 02 µmol h^–1g^–1 f. wt, measured by an in vivo assay, occurred in 41per cent of a large sample (555 species) of woody plants. Ifseveral taxonomic groups (Gymnosperms, Ericaceae and Proteaceae)with consistently low activities were discounted activitiesgreater than 02 µmol h^–1 g^–1 f. wt occurredin 73 per cent of the species. This compares with 93 per centin herbaceous species, suggesting that leaf nitrate reductionis of common occurrence in woody plants. In a small sample ofspecies leaf nitrate reductase activity correlated with nitrateconcentration in the xylem sap. Low activities occurred consistentlyin the Gymnosperms, Ericaceae and Proteaceae. Feeding cut shootsof representatives of these groups with nitrate caused inductionof leaf nitrate reductase activity in the Gymnosperms and Proteaceae,but only limited induction in the Ericaceae. The Ericaceae,with the exception of two species, had low activities and lownitrate reductase inducibility. Root assimilation may predominatein the Gymnosperms and Proteaceae. It is suggested that nitratereduction generally occurs in the leaves of trees from a varietyof plant communities and that this may be related to the lowerenergy cost of leaf, as opposed to root, nitrate assimilation. Nitrate reductase, trees and shrubs, leaves, nitrate assimilation, nitrate translocation, nitrate reductase induction, energy cost, plant ecology     

Nitrate Reductase Acivity in Leaves of Barley (Hordeum vulgare) and Durum Wheat (Triticum durum) during Field and Rapidly Applied Water Deficits

Smirnoff, N., Winslow, M. D. and Stewart, G. R. 1985. Nitratereductase activity in leaves of barley (Hordeum vulgare) anddurum wheat (Triticum durum) during field and rapidly appliedwater deficits.-J. exp. Bot 36: 1200-1208. The effect of field and rapidly applied water deficits on nitratereductase activity in the leaves of two barley varieties andone durum wheat variety was investigated. In field experimentsplants were subjected to irrigation at different rates in threeMediterranean environments by means of a line source sprinklerirrigation system. The environments differed in rainfall andnitrogen fertility. Plant water potentials decreased from –1.5MPa to between –2.5 and –3.0 MPa as the irrigationrate decreased. Nitrate reductase activity in the leaves ofthese plants during heading was either unaffected or sometimesincreased where the least water was supplied. Nitrate reductaseactivity was highest in the plants growing with an ample nitrogensupply irrespective of water regime. In contrast, seedlingssubject to rapidly applied water stress over 6 d lost 30-85%of their nitrate reductase activity when leaf water potentialfell from between –0.33 and –0.75 MPa to between–O.93 and –2.04 MPa. The decrease was less in theyoung leaves than in the old leaves. Polyethylene glycol inducedosmotic stress resulted in a drop in leaf water potential from–0.20 MPa to between –1.05 and –1.20 MPa alongwith a loss of 40-85% of leaf nitrate reductase activity after48 h. It is suggested that maintenance of nitrate reductase activityin field grown barley and durum wheat plants reflects an acclimationto water deficit Maintenance of nitrate assimilation duringwater stress may allow continued synthesis of nitrogenous compatiblesolutes using the excess photochemical energy available duringstomatal closure. Key words: Nitrate reductase, water stress, barley, durum wheat     

Plutella australiana (Lepidoptera,Plutellidae), an overlooked diamondback moth revealed?by?DNA?barcodes

The genus Plutella was thought to be represented in Australia by a single introduced species, Plutella xylostella (Linnaeus), the diamondback moth. Its status as a major pest of cruciferous crops, and the difficulty in developing control strategies has motivated broad-ranging studies on its biology. Prior genetic work has generally supported the conclusion that populations of this migratory species are connected by substantial gene flow. However, the present study reveals the presence of two genetically divergent lineages of this taxonin Australia. One shows close genetic and morphological similarity with the nearly cosmopolitan Plutella xylostella. The second lineage possesses a similar external morphology, but marked sequence divergence in the barcode region of the cytochrome c oxidase I gene, coupled with clear differences in genitalia. As a consequence, members of this lineage are described as a new species, Plutella australiana Landry & Hebert, which is broadly distributed in the eastern half of Australia.     

Physiology of the interaction of angiosperm parasites and their higher plant hosts

Abstract. Interactions between parasitic angiosperms and their hosts occur at the level of seed germination, haustorial development and resource transfer. Chemicals released from the host function as cues for host recognition, and trigger germination as well as haustorial initiation. Transpiration is a key process regulating solute transfer from host to parasite, and some parasitie plants have unusual stomatal characteristics. Although solute transfer is apoplastic, the haustorium appears to play a role in regulating solute composition. Host responses to infection are reviewed, and it is concluded that competition for water and solutes are unlikely to play a major role in determining reductions in host productivity: metabolic incompatability is suggested to be the major cause of this.     

Mechanisms of intracranial kinetics in fossil rhipidistian fishes (Crossopterygii) and their relatives

The fishes of the Order Crossopterygii are characterized by a unique articulation within the braincase, by which the anterior division of the endocranium may be moved dorso-ventrally with respect to the posterior division. The structure of the skull in both groups of crossoptery-gian fishes (the fossil Rhipidistia and the fossil and Recent Coelacanthini) is such that 'normal' operation of the intracranial mechanism involves lateral movements of the cheek region and palate corresponding to the dorso-ventral movements of the ethmoid portion of the braincase. The hyomandibular has a function of prime importance in integrating the movements of the various skull components relative to each other. There are important differences between the characteristic intracranial mechanisms of Rhipidistia and Coelacanthini which may be interpreted in adaptive as well as morphological terms. Analysis of the intracranial kinetics of the Rhipidistia reveals a trend, in certain lines, for the amount of relative movement between the skull components to be decreased and this may be used to explain the loss of the intracranial joint in the Amphibia during their evolution from the Rhipidistia. The functional significance of the intracranial articulation has both a kinetic and a dynamic aspect and while in the Amphibia the kinetic ability of the skull is almost wholly restricted, the dynamic features of the ancestral condition are modified and developed as the basal articulation between the palate and endocranium is retained.     

15N natural abundance of vascular rainforest epiphytes: implications for nitrogen source and acquisition

The foliar natural abundance of ¹⁵N was analysed to compare the potential nitrogen sources of vascular rainforest epiphytes and associated soil-rooted trees. Leaves of epiphytes collected from six rainforest communities in Brazil, Australia and the Solomon Islands were depleted in ¹⁵N relative to the trees at each site. Epiphyte δ¹⁵N was as low as -6.4%_o, while trees were generally enriched in ¹⁵N (0.7 to 3.5%_o). These results indicate either that epiphytes use nitrogen sources depleted in ¹⁵N or that discrimination against ¹⁵N is an intrinsic function of epiphyte physiology. At three sites, epiphytes could be grouped into those having both low δ¹⁵N and low leaf-nitrogen content and those possessing both high δ¹⁵N and high leaf-nitrogen content. The second group had δ¹⁵N values in the range sometimes attributable to N₂ fixation (-2 to 0%o). There was no correlation between growth form and δ¹⁵N. It is concluded that epiphytes may utilize ¹⁵N-depleted nitrogen from atmospheric deposition and N₂ fixation.