Planktothrix populations in subalpine lakes: selection for strains with strong gas vesicles as a function of lake depth,morphometry and circulation

1. The genus Planktothrix (Cyanobacteria) usually produces concentrated populations of filaments in the summer metalimnion of thermally stratifying lakes. This has been associated with the action of gas vesicles, cellular structures providing positive buoyancy. At the end of the summer, filaments are carried by convective mixing deeper into the water column where some gas vesicles collapse as a result of high hydrostatic pressure. They then lose their buoyancy, sink and are lost from the euphotic zone. 2. The resistance of gas vesicles to hydrostatic pressures is critical for the survival of Planktothrix in deep lakes. However, comparative observations on populations from lakes of a range of depths and hydrodynamic regimes are still needed to examine the relationships between the adaptive trait (i.e. the ‘critical’ pressure at which each gas vesicle collapses) with the environmental factor (i.e. the maximum hydrostatic pressure). 3. To explore the adaptation of Planktothrix populations to the depth of winter circulation in different systems, we collected 276 strains of P. cf. rubescens from eight lakes (z_max = 24–410 m) in Northern Italy during summer 2009 and we analysed the multicopy gene gvpC coding for a protein that crucially influences the critical pressure. 4. The strains analysed clustered into two main groups having gas vesicles with a mean critical pressure of 1.1 and 0.9 MPa, respectively. The proportion of the stronger strains was generally positively related to lake depth, although the overall pattern was complicated by individual lake morphology and hydrology. The relative frequency of stronger filaments was (i) greatest in deep basins with concave slopes and (ii) least in one deep, but permanently stratified lake. 5. The simultaneous presence of ‘weaker’ and ‘stronger’ filaments could allow for a rapid adaptive response to changes in hydrostatic pressures, related to changes in the amplitude of vertical circulation characterising deep lakes.     

Conjugation Rescue of Exocytosis Mutants in Tetrahymena thermophila Indicates the Presence of Functional Intermediates in the Regulated Secretory Pathway

ABSTRACT. Tetrahymena thermophila possesses a regulated secretory pathway in which mucin proteins are stored in dense-core granules, called mucocysts. Exocytosis-defective mutants exist that fail to secrete mucin in response to secretagogues. Four of the mutants (SB281, SB283, SB285 and SB715) appear to be blocked at different steps of the regulated secretory pathway. SB281 and SB285 accumulate mucin proteins in heterogeneous cytoplasmic organelles which have not yet been identified; SB283 makes mucocyst-like structures but they contain no immunologically identifiable 80-kDa or 50-kDa mucin proteins; and SB715 has more than normal amounts of immature and undocked mucocysts. The organelles that accumulate in exocytosis-defective mutants could be either normal intermediates in the biosynthetic pathway or aberrant structures that form as a result of the mutations. We have used conjugation rescue to analyze steps in the biogenesis of exocytosis-competent mucocysts and to identify functional intermediates. The cytoplasmic organelles that accumulate in SB281 appear to be unidentified biosynthetic intermediates, and the defect is in a cytosolic protein essential for mucocyst maturation. The organelles which accumulate in the other mutants are likely biosynthetic, but their mutations are in proteins which are labile or not free to diffuse into the mutant conjugant.     

Stimulation of Net Photosynthesis in Cucumber Leaf Discs: Effect of K-Glyoxylate and KCL

Incubation of leaf discs of Cucumis sativus in 15 mol m^–3K-glyoxylate (pH 4.6) doubled the rate of net photosynthesisat limiting CO₂ or HCO^–₃ compared with discs floated ondistilled water. When both control and treated discs were incubatedin Mes-TMAOH buffer at pH 5.0, K-glyoxylate still increasednet photosynthesis by as much as 70%. The tetramethylammoniumsalt (TMA-glyoxylate) was without effect but KCl enhanced netphotosynthesis. Both KCl and K-glyoxylate increased stomatalaperture at pH 5.0. At pH 7.5 (Mops-TMAOH), neither stomatalaperture or photosynthesis was altered by K-glyoxylate, KClor TMA-glyoxylate. None of these salts was found to stimulatephotosynthesis in isolated cucumber mesophyll cells over a rangeof pH values although the cells incorporated as much ¹⁴C-glyoxylateas did leaf discs. The data suggest that enhanced photosynthesisin leaf discs is not due directly to a stimulation of mesophyllcell photosynthesis but rather is a consequence of increasedCO₂ availability and decreased stomatal resistance at low pHin the presence of potassium. Key words: Cucumber, Photosynthesis, Potassium glyoxylate     

Collisional Spectroscopy in Structural Characterization of Melanins: I. A First Study on |C8H7ON|+· Ions Originating From Pyrolysis of Biosynthetic and Synthetic Tryptophan Melanins

The structural investigation of four bio- and synthetic melanins, obtained by the action of polyphenol oxidase from potatoes and Psalliota campestris mushrooms and of tyrosinase from Sepia officinalis on tryptophan, or by means of performic oxidation, has been carried out by thermal decomposition performed in the ion source of a mass spectrometer. The structural characterization of the ionic species |C₈H₇ON|⁺· common and abundant for all the examined compounds, has been obtained by accurate mass measurements and collisional spectroscopy. These mass spectrometric techniques have shown unequivocally for ionic species | C₈H₇ON| ⁺· the structure of 2-indolinone.     

The Extent of Algal and Bacterial Endosymbioses in Protozoa1,2

Long neglected has been the extensive and more or less intimate association of protozoa with a wide variety of other cells, either prokaryotic or eukaryotic in nature. Yet study of such relationships can provide important information concerning certain basic aspects of cellular evolution in general. A survey is offered here of the whole range of such symbiotic associations (i.e. with species of protozoa serving as hosts) with the purposes of drawing attention to the exciting possibilities of such research and of reviewing significant findings made to date. Because of the vastness of the overall field, examples and discussion are primarily limited to consideration of the following major studies: methanogenic bacteria in certain ciliates, bacterial endosymbionts of the large freshwater amoeba Pelomyxa palustris (itself an amazing organism from an evolutionary/phylogenetic point of view), the rod-shaped bacteria found in Amoeba proteus, the “Greek-letter” prokaryotes of Paramecium species, the xenosomes (sensu stricto) of the marine scuticociliate Parauronema acutum, and the diverse algal endosymbionts of similarly diverse protozoan taxa–ciliates, flagellates, radiolarians, acantharians, and foraminifera.     

The Archaeology of Food Preference

Food preference is a socially constructed concept in which both consumers and producers define what is "good to eat." Staple crops and daily meals are an important component of these definitions, as the regular use of particular foods reinforces norms of identity. Food preferences also affect agricultural systems because choices among cultivars are based on social needs in addition to economic variables such as yield and caloric value. Through textual and archaeological evidence, the trajectory of rice production is examined for Sri Lanka, the Brahmaputra Valley, the Tamil region, and Vijayanagara. In these regions and elsewhere in South Asia, shared ideologies of food preference resulted in a consensus mode of agricultural production: Irrigation works increased the tax base for political leaders and the donation base for temple economies, but they also benefited local inhabitants who would have been able to partake of a preferred food on a more regular basis.     

Diagnostic assessment of European gross primary production

We present an approach to estimate gross primary production (GPP) using a remotely sensed biophysical vegetation product (fraction of absorbed photosynthetically active radiation, FAPAR) from the European Commission Joint Research Centre (JRC) in conjunction with GPP estimates from eddy covariance measurement towers in Europe. By analysing the relationship between the cumulative growing season FAPAR and annual GPP by vegetation type, we find that the former can be used to accurately predict the latter. The root mean square error of prediction is of the order of 250 gC m⁻² yr⁻¹. The cumulative growing season FAPAR integrates over a number of effects relevant for GPP such as the length of the growing season, the vegetation's response to environmental conditions and the amount of light harvested that is available for photosynthesis. We corroborate the proposed GPP estimate (noted FAPAR-based productivity assessment+land cover, FPA+LC) on the continental scale with results from the MOD17+radiation-use efficiency model, an artificial neural network up-scaling approach (ANN) and the Lund–Potsdam–Jena managed Land biosphere model (LPJmL). The closest agreement of the mean spatial GPP pattern among the four models is between FPA+LC and ANN (R²= 0.74). At least some of the discrepancy between FPA-LC and the other models result from biases of meteorological forcing fields for MOD17+, ANN and LPJmL. Our analysis further implies that meteorological information is to a large degree redundant for GPP estimation when using the JRC-FAPAR. A major advantage of the FPA+LC approach presented in this paper lies in its simplicity and that it requires no additional meteorological input driver data that commonly introduce substantial uncertainty. We find that results from different data-oriented models may be robust enough to evaluate process-oriented models regarding the mean spatial pattern of GPP, while there is too little consensus among the diagnostic models for such purpose regarding inter-annual variability.