The effect of predation on the structure and invasibility of assembled communities

Summary Fifty four microcosmic communities were assembled over 4 months from a 28-species source pool of phytoplankton using nine different invasion patterns each replicated six times. Three communities from each set of replicates then were invaded with a cladoceran that feeds on phytoplankton. All communities were then treated identically for an additional 4 months. In all nine invasion categories species richness was greater in predated communities. Predation opened communities to invasion by increasing the representation of infrequently sampled species at the expense of more common species. Invasion rate was four times more influential than predation and over eleven times more important than either invasion order or the timing pattern of interspecific arrivals in determining species richness in this system of communitites.     

Limiting factors for seed production in Cynoglossum officinale

Summary Over three years of study, small plants of Cynoglossum officinale consistently produced more flowers per unit of dry weight than large plants. In contrast to earlier results, weight of all seeds tended to increase more than proportional to size. As a result a positive correlation existed between seed set per flower and plant size. The correlation between the mean number of pollinator visits per flower and size was positive but not significant. In a field experiment we found that resources rather than pollen were limiting seed set. Thus, it is unlikely that enhanced pollination of the largest plants causes the size-dependency of seed set per flower. Alternative hypotheses are discussed briefly.Publication of the Meijendel Comité, New Series No. 96     

Poly(gamma-glutamylcysteinyl)glycine Synthesis in Datura innoxia and Binding with Cadmium : Role in Cadmium Tolerance

The effects of Cd on poly(γ-glutamylcysteinyl)glycine [(γEC)_nG] biosynthesis and formation of (γEC)_nG:Cd complexes were measured in two cell lines of Datura innoxia with differing Cd tolerance. In addition, RNA synthesis, protein synthesis, and GSH concentrations were measured during a 48 hour exposure to Cd. Exposure to 250 micromolar CdCl₂ was toxic to the sensitive line, whereas the tolerant line survived and grew in its presence. Cd-sensitive cells synthesized the same amount of (γEC)_nG as tolerant cells during an initial 24 hour exposure to 250 micromolar CdCl₂. However, rates of (γEC)_nG:Cd complex formation differed between the two cell lines with the sensitive cells forming complexes later than tolerant cells. In addition, the complexes formed by sensitive cells were of lower molecular weight than those of tolerant cells and did not bind all of the cellular Cd. Pulse-labeling of cells with l-[³⁵S]cysteine resulted in equivalent rates of incorporation into the (γEC)_nG of both cell lines during the initial 24 hours after Cd. Rates of protein and RNA synthesis were similar for both cell lines during the initial 8 hours after Cd but thereafter declined rapidly in sensitive cells. This was reflected by a decline in viability of sensitive cells. The GSH content of both cell lines declined rapidly upon exposure to Cd but was higher in sensitive cells throughout the experiment. These results show that the biosynthetic pathway for (γEC)_nG synthesis in sensitive cells is operational and that relative overproduction of (γEC)_nG is not the mechanism of Cd-tolerance in a Cd-tolerant cell line of D. innoxia. Rapid formation of (γEC)_nG:Cd complexes that bind all of the cellular Cd within 24 hours appears to correlate with tolerance in these cells.     

Phosphoribosyl pyrophosphate and the measurement on inorganic pyrophosphate in plant tissues

This work provides further evidence that plants contain appreciable amounts of inorganic pyrophosphate (PPi), and that breakdown of phosphoribosyl pyrophosphate (PPRibP) does not contribute significantly to the PPi detected in plant extracts. Inorganic pyrophosphate in extracts of the roots of Pisum sativum L., clubs of the spadices of Arum maculatum L., and the developing endosperm of Zea mays L. was assayed with pyrophosphate fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90), and with sulphate adenyltransferase (EC 2.7.7.4). The two different assays gave the same value for PPi content, and for recovery of added PPi. It was shown that PPRibP is converted to PPi during the extraction of PPi. However, the amounts of PPRibP in clubs of A. maculatum and the developing endosperm of Z. mays were negligible in comparison with the contents of PPi.Abbreviations EDTA ethylenediaminetetraacetic acid - PFK(PPi) pyrophosphate fructose 6-phosphate 1-phosphotransferase - PPi inorganic pyrophosphate - PPRibP phosphoribosyl pyrophosphate     

Legumin antibodies recognize polypeptides in coated vesicles isolated from developing pea cotyledons

Summary A highly enriched coated vesicle fraction has been isolated from cotyledons of developing pea seeds. This, and coated vesicles isolated from bovine brain as well as from bean leaves were subjected to SDS-PAGE followed by Western blotting with legumin antibodies. A distinct cross reaction with two polypeptides at around 60 kDa was seen, but only with the coated vesicles isolated from peas. Since legumin is synthesized as a 60 kDa precursor, but occurs as 40 and 20 kDa polypeptides in the protein body, we interpret our results as giving support to the idea that reserve proteins, like lysosomal proteins, are transported via coated vesicles.Abbreviations CV coated vesicle - DTT dithiothreitol - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis     

Lysophosphatidylcholine metabolism and lipoprotein secretion by cultured rat hepatocytes deficient in choline.

A protein kinase activity was identified in pig brain that co-purified with microtubules through repeated cycles of temperature-dependent assembly and disassembly. The microtubule-associated protein kinase (MTAK) phosphorylated histone H1; this activity was not stimulated by cyclic nucleotides. Ca2+ plus calmodulin, phospholipids or polyamines. MTAK did not phosphorylate synthetic peptides which are substrates for cyclic AMP-dependent protein kinase, cyclic GMP-dependent protein kinase. Ca2+/calmodulin-dependent protein kinase II, protein kinase C or casein kinase II. MTAK activity was inhibited by trifluoperazine [IC50 (median inhibitory concn.) = 600 microM] in a Ca2+-independent fashion. Ca2+ alone was inhibitory [IC50 = 4 mM). MTAK was not inhibited by heparin, a potent inhibitor of casein kinase II, nor a synthetic peptide inhibitor of cyclic AMP-dependent protein kinase. MTAK demonstrated a broad pH maximum (7.5-8.5) and an apparent Km for ATP of 45 microM. Mg2+ was required for enzyme activity and could not be replaced by Mn2+. MTAK phosphorylated serine and threonine residues on histone H1. MTAK is a unique cofactor-independent protein kinase that binds to microtubule structures.     

Circannual cycles of luteinizing hormone and prolactin secretion in ewes during prolonged exposure to a fixed photoperiod: evidence for an endogenous reproductive rhythm

Circulating patterns of luteinizing hormone (LH) and prolactin (PRL) were monitored for 5 yr in ewes maintained either outdoors in natural conditions or indoors in a fixed, short photoperiod (8L:16D). The ewes were ovariectomized and each was treated with a Silastic implant containing estradiol to provide a fixed negative feedback signal to the reproductive neuroendocrine axis. Serum concentrations of LH and PRL were subjected to a statistical algorithm developed for the purpose of detecting hormone cycles. In ewes maintained outdoors, serum concentrations of both hormones underwent high amplitude cycles with a period no different from 365 days. Among ewes maintained in the fixed photoperiod, unambiguous cycles of LH and PRL persisted through the 5 yr of exposure to short days. Period of these cycles differed from 365 days. Further, the LH cycles became desynchronized among ewes housed together and desynchronized with respect to the LH cycles in ewes kept outdoors. These findings document the existence of an endogenous circannual rhythm of reproductive neuroendocrine function in ewes.     

Identification of the molecular species of lysophosphatidic acid produced when platelets are stimulated by thrombin

Platelets, when stirred with 3 U thrombin/10(9) platelets, produced significant quantities of palmitoyllysophosphatidic acid (2.17 ng/10(9) platelets), stearoyllysophosphatidic acid (2.11 ng/10(9) platelets), and arachidonoyllysophosphatidic acid (1.06 ng/10(9) platelets). When platelets were pretreated with 100 microM of the phospholipase A2 inhibitor U10029A, there was a significant decrease in thrombin-stimulated production of stearoyllysophosphatidic acid (to 0.16 ng/10(9) platelets), while arachidonoyllysophosphatidic acid production was unchanged. U10029A concomitantly increased thrombin-stimulated production of stearoyl-containing phosphatidic acid species (primarily stearoylarachidonoylphosphatidic acid) from 5.99 to 9.71 ng/10(9) platelets. The results are consistent with the concept that stearoyllysophosphatidic acid production in platelets occurs via phospholipase A2 degradation of phosphatidic acid.     

Induction of T4 DNA ligase in a recombinant strain of Escherichia coli

The kinetics of cell growth and foreign protein production, as well as factors affecting protein stability, were studied and optimized in batch and fed-batch fermentations of a recombinant strain of Escherichia coli. The pL promoter from bacteriophage lambda under the control of a temperature-sensitive cl represser, with the entire construct integrated into the E. coli chromosome through the use of a defective bacteriophage lambda lysogen, was used to direct the synthesis of T4 DNA ligase. The biphasic fermentations consisted of a primary growth phase at 30 degrees C followed by an induction phase which was initiated by shifting the temperature to 42 degrees C. In the fed-batch fermentations, additional nutrients were added at the time of initiating induction. Maintenance of sufficiently high concentrations of the organic substrates (glucose and casamino acids) during the induction phase was required for continued cell growth at 42 degrees C. Such growth was essential for T4 DNA ligase formation and in vivo stability. Hence, fed-batch fermentations produced the highest yield of the foreign protein Commensurate with providing lower total amounts of substrates. In such cases, high cell densities (6 g dry wt/L) with substantial intracellular levels of T4 DNA ligase (4.6% total cellular protein, or 2.7% of the dry biomass) were achieved.     

TGF-beta 1-induced inhibition of mouse mammary ductal growth: developmental specificity and characterization

TGF-beta 1, implanted into growing mouse mammary glands, was previously shown to inhibit ductal growth in an apparently normal and fully reversible manner. In this report we extend these findings to show that TGF-beta 1 inhibition is highly specific. In pregnant or hormone-treated mice, doses of TGF-beta 1 that were capable of fully inhibiting ductal elongation had little effect on the proliferation of lobuloalveolar structures. Additionally, the inhibitory action of TGF-beta 1 on ducts is epithelium-specific, resulting in cessation of DNA synthesis in the rapidly proliferating epithelium of mammary end buds, but does not inhibit DNA synthesis in the stroma surrounding the end buds. At the cellular level, transplant studies showed that TGF-beta 1 inhibited the regeneration of mammary ductal cells when implanted into mammary gland-free fat pads by suppressing the formation of new end buds, without inhibiting maintenance DNA synthesis in ductal lumenal epithelium; this observation indicates the potential of TGF-beta 1 to maintain patterning by suppressing adventitious lateral branching. The time-course of TGF-beta 1 inhibition of end buds was rapid, with cessation of DNA synthesis by 12 hr, followed by loss of the stem cell (cap cell) layer. The question of glandular exposure to TGF-beta 1 administered in EVAc implants was also investigated. Incorporation of TGF-beta 1 into EVAc was found not to degrade the hormone, while the release kinetics of the ligand from implants, its retention in the gland, and the demonstrable zone of exposure were consistent with observed inhibitory effects. These results support the hypothesis that TGF-beta 1 is a natural regulator of mammary ductal growth.