AMP photophosphorylation and binding by chloroplasts

Stoichiometric amounts of chloroplast thylakoids photophosphorylate free AMP to tightly bound ADP. Free ADP is a poor competitor for this AMP photoreaction, which saturates below 16 micronAMP. The inhibitor, diadenosine pentaphosphate, abolishes AMP photophosphorylation, and inhibits dark ADP binding. Taken together, these data imply that this photoreaction involves the high affinity nucleotide binding site(s) of chloroplast coupling factor CF1, and that little mixing with free nucleotides occurs.     

Pre- and Posttranslational Regulation of β-Endorphin Biosynthesis in the CNS: Effects of Chronic Naltrexone Treatment

Abstract: There appear to be two anatomically distinct β-endorphin (βE) pathways in the brain, the major one originating in the arcuate nucleus of the hypothalamus and a smaller one in the area of the nucleus tractus solitarius (NTS) of the caudal medulla. Previous studies have shown that these two proopiomelanocortin (POMC) systems may be differentially regulated by chronic morphine treatment, with arcuate cells down-regulated and NTS cells unaffected. In the present experiments, we examined the effects of chronic opiate antagonist treatment on βE biosynthesis across different CNS regions to assess whether the arcuate POMC system would be regulated in the opposite direction to that seen after opiate agonist treatment and to determine whether different βE-containing areas might be differentially regulated. Male adult rats were administered naltrexone (NTX) by various routes for 8 days (subcutaneous pellets, osmotic minipumps, or repeated intraperitoneal injections). Brain and spinal cord regions were assayed for total βE-ir, different molecular weight immunoreactive β-endorphin (βE-ir) peptides, and POMC mRNA. Chronic NTX treatment, regardless of the route of administration, reduced total βE-ir concentrations by 30–40% in diencephalic areas (the arcuate nucleus, the remaining hypothalamus, and the thalamus) and the midbrain, but had no effect on βE-ir in the NTS or any region of the spinal cord. At the same time, NTX pelleting increased POMC mRNA levels in the arcuate to ～ 140% of control values. These data suggest that arcuate POMC neurons are up-regulated after chronic NTX treatment (whereas NTS and spinal cord systems remain unaffected) and that they appear to be under tonic inhibition by endogenous opioids. Chromatographic analyses demonstrated that, after chronic NTX pelleting, the ratio of full length βE_1–31 to more processed βE-ir peptides (i.e., βE_1–27 and βE_1–26) tended to increase in a dose-dependent manner in diencephalic areas. Because βE_1–31 is the only POMC product that possesses opioid agonist properties, and βE_1–27 has been posited to function as an endogenous anatgonist of βE_1–31, the NTX-induced changes in the relative concentrations of βE_1–31 and βE_1–27/βE_1–26 may represent a novel regulatory mechanism of POMC cells to alter the opioid signal in the synapse.     

A General Scheme to Predict Partner Control Mechanisms in Pairwise Cooperative Interactions Between Unrelated Individuals

Recent years have seen an explosion in the diversity of partner control mechanisms hypothesised to stabilise cooperative behaviour among unrelated individuals. Game theory suggests numerous strategies, each with specific decision rules that allow cooperators to control a non‐contributing partner. This diversity of hypothetical strategies seems likely to reflect diversity in the types of intraspecific cooperation and interspecific mutualism that exist in nature. It is therefore important to provide a framework that explains similarities and differences between the various hypothetical strategies and that predicts how key parameters that describe the natural history of natural systems favour different control mechanisms. We develop a novel unifying framework for pairwise interactions between unrelated individuals, in which we link specific control mechanisms to specific game structures. The latter are defined by unique combinations of the states of five parameters that describe investment, aspects of the payoff matrix, the number of interactions and partner choice. We find that specific control mechanisms potentially have utility in a limited number of game structures; conversely, each game structure may typically offer a few competing control mechanisms. Our framework offers theoreticians specific problems that await mathematical exploration, while at the same time offering empiricists guidelines for evaluating the game structure and corresponding control mechanisms in their systems.     

Conditional outcomes in mutualistic interactions

Interspecific interactions are traditionally displayed in a grid in which each interaction is placed according to its outcome (positive, negative or neutral) for each partner. However, recent field studies consistently find the costs and benefits that determine net effects to vary greatly in both space and time, inevitably causing outcomes within most interactions to vary as well. Interactions show 'conditionality' when costs and benefits, and thus outcomes, are affected in predictable ways by current ecological conditions. The full range of natural outcomes of a given association may reveal far more about its ecological and evolutionary dynamics than does the average outcome at a given place and time.     

Competition for nectar resources does not affect bee foraging tactic constancy

1. Competition alters animal foraging, including promoting the use of alternative resources. It may also impact how animals feed when they are able to handle the same food with more than one tactic. Competition likely impacts both consumers and their resources through its effects on food handling, but this topic has received little attention. 2. Bees often use two tactics for extracting nectar from flowers: they can visit at the flower opening, or rob nectar from holes at the base of flowers. Exploitative competition for nectar is thought to promote nectar robbing. If so, higher competition among floral visitors should reduce constancy to a single foraging tactic as foragers will seek food using all possible tactics. To test this prediction, field observations and two experiments involving bumble bees visiting three montane Colorado plant species (Mertensia ciliata, Linaria vulgaris, Corydalis caseana) were used under various levels of inter- and intra-specific competition for nectar. 3. In general, individual bumble bees remained constant to a single foraging tactic, independent of competition levels. However, bees that visited M. ciliata in field observations decreased their constancy and increased nectar robbing rates as visitation rates by co-visitors increased. 4. While tactic constancy was high overall regardless of competition intensity, this study highlights some intriguing instances in which competition and tactic constancy may be linked. Further studies investigating the cognitive underpinnings of tactic constancy should provide insight on the ways in which animals use alternative foraging tactics to exploit resources.     

HopPtoN is a Pseudomonas syringae Hrp (type III secretion system) cysteine protease effector that suppresses pathogen-induced necrosis associated with both compatible and incompatible plant interactions

Pseudomonas syringae pv. tomato DC3000 causes bacterial speck disease in tomato, and it elicits the hypersensitive response (HR) in non-host plants such as Nicotiana tabacum and Nicotiana benthamiana. The compatible and incompatible interactions of DC3000 with tomato and Nicotiana spp., respectively, result in plant cell death, but the HR cell death occurs more rapidly and is associated with effective plant defense. Both interactions require the Hrp (HR and pathogenicity) type III secretion system (TTSS), which injects Hop (Hrp outer protein) effectors into plant cells. Here, we demonstrate that HopPtoN is translocated into tomato cells via the Hrp TTSS. A hopPtoN mutant produced eightfold more necrotic 'speck' lesions on tomato leaves than did DC3000, but the mutant and the wild-type strain grew to the same level in infected leaves. In non-host N. tabacum leaves, the hopPtoN mutant produced more cell death, whereas a DC3000 strain overexpressing HopPtoN produced less cell death and associated electrolyte leakage in comparison with wild-type DC3000. Transient expression of HopPtoN via infection with a PVX viral vector enabled tomato and N. benthamiana plants to tolerate, with reduced disease lesions, challenge infections with DC3000 and P. syringae pv. tabaci 11528, respectively. HopPtoN showed cysteine protease activity in vitro, and hopPtoN mutants altered in the predicted cysteine protease catalytic triad (C172S, H283A and D299A) lost HR suppression activity. These observations reveal that HopPtoN is a TTSS effector that can suppress plant cell death events in both compatible and incompatible interactions.     

OSP/claudin-11 forms a complex with a novel member of the tetraspanin super family and beta1 integrin and regulates proliferation and migration of oligodendrocytes

Oligodendrocyte-specific protein (OSP)/claudin-11 is a major component of central nervous system myelin and forms tight junctions (TJs) within myelin sheaths. TJs are essential for forming a paracellular barrier and have been implicated in the regulation of growth and differentiation via signal transduction pathways. We have identified an OSP/claudin-11-associated protein (OAP)1, using a yeast two-hybrid screen. OAP-1 is a novel member of the tetraspanin superfamily, and it is widely expressed in several cell types, including oligodendrocytes. OAP-1, OSP/claudin-11, and beta1 integrin form a complex as indicated by coimmunoprecipitation and confocal immunocytochemistry. Overexpression of OSP/claudin-11 or OAP-1 induced proliferation in an oligodendrocyte cell line. Anti-OAP-1, anti-OSP/claudin-11, and anti-beta1 integrin antibodies inhibited migration of primary oligodendrocytes, and migration was impaired in OSP/claudin-11-deficient primary oligodendrocytes. These data suggest a role for OSP/claudin-11, OAP-1, and beta1 integrin complex in regulating proliferation and migration of oligodendrocytes, a process essential for normal myelination and repair.     

Cyanobacterial sulfide-quinone reductase: cloning and heterologous expression

The gene encoding sulfide-quinone reductase (SQR; E.C.1.8.5.'), the enzyme catalyzing the first step of anoxygenic photosynthesis in the filamentous cyanobacterium Oscillatoria limnetica, was cloned by use of amino acid sequences of tryptic peptides as well as sequences conserved in the Rhodobacter capsulatus SQR and in an open reading frame found in the genome of Aquifex aeolicus. SQR activity was also detected in the unicellular cyanobacterium Aphanothece halophytica following sulfide induction, with a V(max) of 180 micromol of plastoquinone-1 (PQ-1) reduced/mg of chlorophyll/h and apparent K(m) values of 20 and 40 microM for sulfide and quinone, respectively. Based on the conserved sequences, the gene encoding A. halophytica SQR was also cloned. The SQR polypeptides deduced from the two cyanobacterial genes consist of 436 amino acids for O. limnetica SQR and 437 amino acids for A. halophytica SQR and show 58% identity and 74% similarity. The calculated molecular mass is about 48 kDa for both proteins; the theoretical isoelectric points are 7.7 and 5.6 and the net charges at a neutral pH are 0 and -14 for O. limnetica SQR and A. halophytica SQR, respectively. A search of databases showed SQR homologs in the genomes of the cyanobacterium Anabaena PCC7120 as well as the chemolithotrophic bacteria Shewanella putrefaciens and Thiobacillus ferrooxidans. All SQR enzymes contain characteristic flavin adenine dinucleotide binding fingerprints. The cyanobacterial proteins were expressed in Escherichia coli under the control of the T7 promoter. Membranes isolated from E. coli cells expressing A. halophytica SQR performed sulfide-dependent PQ-1 reduction that was sensitive to the quinone analog inhibitor 2n-nonyl-4-hydroxyquinoline-N-oxide. The wide distribution of SQR genes emphasizes the important role of SQR in the sulfur cycle in nature.     

Later flowering is associated with a compressed flowering season and reduced reproductive output in an early season floral resource

Climate change‐induced shifts in flowering phenology can expose plants to novel biotic and abiotic environments, potentially leading to decreased temporal overlap with pollinators and exposure to conditions that negatively affect fruit and seed set. We explored the relationship between flowering phenology and reproductive output in the common shrub pointleaf manzanita Arctostaphylos pungens in a lower montane habitat in southeastern Arizona, USA. Contrary to the pattern of progressively earlier flowering observed in many species, long‐term records show that A. pungens flowering onset is shifting later and the flowering season is being compressed. This species can thus provide unusual insight into the effects of altered phenology. To determine the consequences of among‐ and within‐plant variation in flowering time, we documented individual flowering schedules and followed the fates of flowers on over 50 plants throughout two seasons (2012 and 2013). We also measured visitation rates by potential pollinators in 2012, as well as both fruit mass and seeds per fruit of flowers produced at different times. Fruit set was positively related to visitation rate but declined with later dates of flower production in both years. Total fruit production per plant was positively influenced by flowering duration, which declined with later flowering onset, as did fruit mass. Individual flowering schedules were consistent between years, suggesting that plants that begin flowering late have lower reproductive output each year. These patterns suggest that if pointleaf manzanita flowering continues to shift later, its flowering season may continue to become shorter, compressing floral resource availability for pollinators and leading to reduced reproductive output. These results reveal the negative effects of delayed phenology on reproductive output in a long‐lived plant. They highlight the value of using natural variation in flowering time, in combination with long‐term data, to anticipate the consequences of phenological shifts.