Midsummer decline of a Daphnia population attributed in part to cyanobacterial capsule production

A midsummer decline in a Daphnia population has been documentedin Lake Winnebago, Wisconsin, USA, similar to that which typicallyoccurs in other freshwater lakes throughout the world. We investigatedthe role of two products of the cyanobacterium Microcystis aeruginosa(microcystin and polysaccharide capsular matrix) in contributingto this population decrease by utilizing laboratory and lakestudies. Feeding on either the microcystin-producing, minimallyencapsulated M. aeruginosa strain PCC 7820 or the highly encapsulated,non-microcystin-producing strain C3-40, resulted in decreasedsurvival when compared with animals fed chlorophytes. The survivorshipof Daphnia fed C3-40 cells washed to remove the capsule increasedby 30% over that seen in animals fed encapsulated C3-40. Feedingpurified microcystin or capsule alone decreased Daphnia survivalto a greater degree than did starvation. Physiological studiesconducted while Daphnia were exposed to these food sources showedthat ingestion of capsular material resulted in increased post-abdominalclaw movements and decreased mandibular movements. Concurrently,elevated respiration rates were measured in Daphnia, implyingthat capsule increased the energy expended by these animalsthrough increased attempts to reject the material and decreasedfood intake. Lake studies reflected the results of the laboratoryexperiments. The midsummer decline of the Daphnia populationoccurs as the Microcystis biovolume increases and both microcystinand capsular matrix levels rise. While both cyanobacterial productsmay contribute to the midsummer decline in Daphnia pulicaria,laboratory studies suggest that encapsulation may play the greaterrole.     

Delta Opioid Receptors: The Link between Exercise and Cardioprotection

This study investigated the role of opioid receptor (OR) subtypes as a mechanism by which endurance exercise promotes cardioprotection against myocardial ischemia-reperfusion (IR) injury. Wistar rats were randomly divided into one of seven experimental groups: 1) control; 2) exercise-trained; 3) exercise-trained plus a non-selective OR antagonist; 4) control sham; 5) exercise-trained plus a kappa OR antagonist; 6) exercise-trained plus a delta OR antagonist; and 7) exercise-trained plus a mu OR antagonist. The exercised animals underwent 4 consecutive days of treadmill training (60 min/day at ∼70% of maximal oxygen consumption). All groups except the sham group were exposed to an in vivo myocardial IR insult, and the myocardial infarct size (IS) was determined histologically. Myocardial capillary density, OR subtype expression, heat shock protein 72 (HSP72) expression, and antioxidant enzyme activity were measured in the hearts of both the exercised and control groups. Exercise training significantly reduced the myocardial IS by approximately 34%. Pharmacological blockade of the kappa or mu OR subtypes did not blunt exercise-induced cardioprotection against IR-mediated infarction, whereas treatment of animals with a non-selective OR antagonist or a delta OR antagonist abolished exercise-induced cardioprotection. Exercise training enhanced the activities of myocardial superoxide dismutase (SOD) and catalase but did not increase the left ventricular capillary density or the mRNA levels of HSP72, SOD, and catalase. In addition, exercise significantly reduced the protein expression of kappa and delta ORs in the heart by 44% and 37%, respectively. Together, these results indicate that ORs contribute to the cardioprotection conferred by endurance exercise, with the delta OR subtype playing a key role in this response.     

Myofibril Changes in the Copepod Pseudodiaptomus marinus Exposed to Haline and Thermal Stresses

Copepods are small crustaceans capable to survive in various aquatic environments. Their responses to changes in different external factors such as salinity and temperature can be observed at different integration levels from copepod genes to copepod communities. Until now, no thorough observation of the temperature or salinity effect stresses on copepods has been done by optical microscopy. In this study, we used autofluorescence to visualize these effects on the morphology of the calanoid copepod Pseudodiaptomus marinus maintained during several generations in the laboratory at favorable and stable conditions of salinity (30 psu) and temperature (18°C). Four different stress experiments were conducted: at a sharp decrease in temperature (18 to 4°C), a moderate decrease in salinity (from 30 to 15 psu), a major decrease in salinity (from 30 to 0 psu), and finally a combined stress with a decrease in both temperature and salinity (from 18°C and 30 psu to 4°C and 0 psu). After these stresses, images acquired by confocal laser scanning microscopy (CLSM) revealed changes in copepod cuticle and muscle structure. Low salinity and/or temperature stresses affected both the detection of fluorescence emitted by muscle sarcomeres and the distance between them. In the remaining paper we will use the term sarcomeres to describe the elements located within sarcomeres and emitted autofluorescence signals. Quantitative study showed an increase in the average distance between two consecutive sarcomeres from 2.06 +/- 0.11 μm to 2.44 +/- 0.42 μm and 2.88 +/- 0.45μm after the exposure to major haline stress (18°C, 0 psu) and the combined stress (4°C, 0 psu), respectively. These stresses also caused cuticle cracks which often occurred at the same location, suggesting the cuticle as a sensitive area for osmoregulation. Our results suggest the use of cuticular and muscle autofluorescence as new biomarkers of stress detectable in formalin-preserved P. marinus individuals. Our label-free method can be easily applied to a large number of other copepod species or invertebrates with striated musculature.     

Role of arbuscular mycorrhizal symbiosis in root mineral uptake under CaCO3 stress

This study investigated the effects of increasing CaCO(3) concentrations (0, 5, 10, 20?mM) on arbuscular mycorrhizal (AM) symbiosis establishment as well as on chicory root growth and mineral nutrient uptake in a monoxenic system. Although CaCO(3) treatments significantly decreased root growth and altered the symbiosis-related development steps of the AM fungus Rhizophagus irregularis (germination, germination hypha elongation, root colonization rate, extraradical hyphal development, sporulation), the fungus was able to completely fulfill its life cycle. Even when root growth decreased more drastically in mycorrhizal roots than in non-mycorrhizal ones in the presence of high CaCO(3) levels, the AM symbiosis was found to be beneficial for root mineral uptake. Significant increases in P, N, Fe, Zn and Cu concentrations were recorded in the mycorrhizal roots. Whereas acid and alkaline phosphatase enzymatic activities remained constant in mycorrhizal roots, they were affected in non-mycorrhizal roots grown in the presence of CaCO(3) when compared with the control.     

In vitro and in vivo investigation of the efficacy of arylimidamide DB1831 and its mesylated salt form--DB1965--against Trypanosoma cruzi infection

Chagas disease is caused by infection with the intracellular protozoan parasite Trypanosoma cruzi. At present, nifurtimox and benznidazole, both compounds developed empirically over four decades ago, represent the chemotherapeutic arsenal for treating this highly neglected disease. However, both drugs present variable efficacy depending on the geographical area and the occurrence of natural resistance, and are poorly effective against the later chronic stage. As a part of a search for new therapeutic opportunities to treat chagasic patients, pre-clinical studies were performed to characterize the activity of a novel arylimidamide (AIA--DB1831 (hydrochloride salt) and DB1965 (mesylate salt)) against T. cruzi. These AIAs displayed a high trypanocidal effect in vitro against both relevant forms in mammalian hosts, exhibiting a high selectivity index and a very high efficacy (IC(50) value/48 h of 5-40 nM) against intracellular parasites. DB1965 shows high activity in vivo in acute experimental models (mouse) of T. cruzi, showing a similar effect to benznidazole (Bz) when compared under a scheme of 10 daily consecutive doses with 12.5 mg/kg. Although no parasitological cure was observed after treating with 20 daily consecutive doses, a combined dosage of DB1965 (5 mg/kg) with Bz (50 mg/kg) resulted in parasitaemia clearance and 100% animal survival. In summary, our present data confirmed that aryimidamides represent promising new chemical entities against T. cruzi in therapeutic schemes using the AIA alone or in combination with other drugs, like benznidazole.     

Calcareous impact on arbuscular mycorrhizal fungus development and on lipid peroxidation in monoxenic roots

The present work underlined the negative effects of increasing CaCO₃ concentrations (5, 10 and 20 mM) both on the chicory root growth and the arbuscular mycorrhizal fungus (AMF) Glomus irregulare development in monoxenic system. CaCO₃ was found to reduce drastically the main stages of G. irregulare life cycle (spore germination, germinative hyphae elongation, root colonization, extraradical hyphae development and sporulation) but not to inhibit it completely. The root colonization drop was confirmed by the decrease in the arbuscular mycorrhizal fungal marker C16:1ω5 amounts in the mycorrhizal chicory roots grown in the presence of CaCO₃. Oxidative damage evaluated by lipid peroxidation increase measured by (i) malondialdehyde (MDA) production and (ii) the antioxidant enzyme peroxidase (POD) activities, was highlighted in chicory roots grown in the presence of CaCO₃. However, MDA formation was significantly higher in non-mycorrhizal roots as compared to mycorrhizal ones. This study pointed out the ability of arbuscular mycorrhizal symbiosis to enhance plant tolerance to high levels of CaCO₃ by preventing lipid peroxidation and so less cell membrane damage.     

Frost increases beech susceptibility to scolytine ambrosia beetles

• 1 In the early 2000s, beech forests in Western Europe suffered from a so far unexplained burst of mortality. Necroses, ambrosia‐beetle and fungal attacks were observed on the trunks. The symptoms were similar to previous events reported throughout the 20th Century.
• 2 One current hypothesis is that these phenomena were related to early frost events for which the trees were physiologically unprepared and which made them vulnerable to biotic attacks. In the present study, we aimed to test this hypothesis further, by retrospective meteorological analyses and also by an experimental approach.
• 3 Our meteorological analyses highlighted the occurrence of cold waves a year before the beech declines were reported in 1929, 1942 and 1998.
• 4 In our experimental approach, frost injuries were inflicted to mature trees in a beech stand using dry ice. The treated trees were more attractive to insects than untreated controls. Insect attacks were observed in the treated zones on the trees but colonization was not very successful. The galleries had aborted most of the time with only a few larval chambers. Very few insects were caught in emergence traps.
• 5 The results of these two approaches support and strengthen the hypothesis that frost induced beech dieback. Frost injuries increased tree attraction to ambrosia beetles to the point of inducing attacks. However, the overall success of these attacks was much lower than that observed in the 2000s. These differences might reflect limitations in our experimental approach, where frost wounding was applied locally to the trees.

     

Effect of chitosan for the control of potato diseases caused by Fusarium species

The antifungal activity of chitosan against Fusarium spp. was investigated based on in vitro and in vivo assays, and its possible modes of action were also explored. Chitosan applied at 4.0 g/L of acetic acid-distilled water solution significantly decreased the mycelial growth of Fusarium oxysporum, Fusarium sambucinum and Fusarium graminearum by 88.4%, 89.0% and 89.8%, respectively. Tuber treatment by chitosan (4.0 g/L) of acetic acid-distilled water solution, prior to inoculation, reduced dry rot severity induced by F. oxysporum and F. sambucinum by 60.0% and 48.2%, respectively. When tested as plant treatment, potato plants inoculated with Fusarium species, exhibited 33.5%–45.3% less wilting severity as compared to the control. This abiotic treatment improved the phenolic compounds activities and defence-related enzymes such as peroxidase and polyphenoloxidase in potato tubers inoculated with Fusarium spp. Results clearly demonstrated that chitosan could be explored as an alternative agent to chemical fungicides for the control of tuber dry rot and Fusarium wilt through induction of the plant defence system.