Central and peripheral mechanisms in the control of the diurnal rhythm of flashing in Luciola lusitanica (Charp.)

The mechanisms underlying the diurnal rhythm of flashing in L. lusitanica were investigated. It was shown that the diurnal rhythm of flashing was present also in animals kept in continuous darkness, showing that it was not directly determined by the periodic variations of the ambient light intensity which take place through the nicthemeron. During the hours in which the animals did not flash, photogenic volleys of normal size and contour could still be recorded, although at a lower frequency; however, they were not followed by light emission. Statistical controls ruled out the possibility that the absence of flashing during daytime was due to the reduced repetition rate of the photogenic volleys. The ablation of the gonads performed during day-time was followed by the reappearence of a flash in the wake of each photogenic volley. It is concluded that two mechanism control the diurnal rhythm of flashing, namely; a central mechanism, responsible for the decrease in volley frequency; and a peripheral mechanism, of gonadal origin, which is responsible for the inhibition of the photogenic organ.     

Taurocholate-induced inhibition of hepatic lysosomal degradation of horseradish peroxidase.

Endocytosed proteins in hepatocytes are transported to lysosomes for degradation. Metabolites accumulating in these organelles are released into bile by exocytosis, a process that seems to be regulated by the bile salt taurocholate (TC). In this study we examined if TC is also involved in the control of the lysosomal degradation of endocytosed proteins. We used [(14)C]sucrose-labeled horseradish peroxidase ([(14)C]S-HRP), a probe suitable to evaluate lysosomal proteolysis. TC-infused rats as well as isolated rat hepatocytes exposed to TC showed a significant inhibition in the lysosomal degradation of [(14)C]S-HRP (approximately 30%), with no change in either the uptake or the amount of protein reaching lysosomes. Under these conditions, the in vitro assay of lysosomal cathepsins B, L, H, and D revealed no change in their activities, suggesting that a reversible inhibition (lysosomal alkalinization?) was taking place in hepatocytes. Nevertheless, lysosomal pH measured using fluorescein isothiocyanate-dextran was shown not to be altered by TC. In addition, TC was unable to inhibit proteolysis in [(14)C]S-HRP loaded lysosomes or interfere in cathepsin assays. The results suggest that TC inhibits the lysosomal degradation of endocytosed proteins in hepatocytes and that the mechanism does not involve an effect of the bile salt per se or a rise in lysosomal pH.     

Strong increase of durum wheat iron and zinc content by field-inoculation with arbuscular mycorrhizal fungi at different soil nitrogen availabilities

Background and aims

The changes in the characteristics of Panicum virgatum, an exotic invasive species, after invading various plant communities on the Loess Plateau in China and the main soil nutrient factors in these communities closely associated with invasion remain unclear.

Methods

A pot culture experiment was carried out to simulate the changes in photosynthesis, biomass, and biomass allocation in P. virgatum and to identify the main soil nutrient factors in various soils collected from local plant communities. P. virgatum was grown in soils collected from communities of P. virgatum (PS treatment), Setaria viridis (SS treatment), Bothriochloa ischaemum (BS treatment), and Artemisia sacrorum (AS treatment) and in a mixed soil from the communities of S. viridis, B. ischaemum, and A. sacrorum (MS treatment).

Results

Photosynthesis in P. virgatum differed significantly among the soil treatments. Net photosynthetic rate, stomatal conductance, and photochemical efficiency (Fv/Fm) were highest in PS, whereas single-photon avalanche diode values were highest in PS and SS. The variation of biomass differed significantly in different tissues of P. virgatum in the treatments. Leaf and stem biomasses were highest in PS and SS, and root biomass was highest in PS and MS. Total biomass differed significantly among the treatments, except between BS and MS. Both the leaf to total and stem to total biomass ratios were highest in AS and SS, but the root to total biomass ratio was lowest in these two treatments. A constrained redundancy analysis and a path analysis suggested that the water-soluble nitrate-nitrogen (W-NN) concentration of the soil could significantly affect photosynthesis, biomass, and biomass allocation in P. virgatum.

Conclusions

Photosynthesis, biomass, and biomass allocation in P. virgatum differed significantly when grown in soils from different local plant communities on the Loess Plateau. The soil W-NN concentration in these local plant communities likely has a large impact on the invasive success of P. virgatum.

     

Attenuation of induced bronchoconstriction in healthy subjects: effects of breathing depth.

The effects of breathing depth in attenuating induced bronchoconstriction were studied in 12 healthy subjects. On four separate, randomized occasions, the depth of a series of five breaths taken soon (approximately 1 min) after methacholine (MCh) inhalation was varied from spontaneous tidal volume to lung volumes terminating at approximately 80, approximately 90, and 100% of total lung capacity (TLC). Partial forced expiratory flow at 40% of control forced vital capacity (V(part)) and residual volume (RV) were measured at control and again at 2, 7, and 11 min after MCh. The decrease in V(part) and the increase in RV were significantly less when the depth of the five-breath series was progressively increased (P < 0.001), with a linear relationship. The attenuating effects of deep breaths of any amplitude were significantly greater on RV than V(part) (P < 0.01) and lasted as long as 11 min, despite a slight decrease with time when the end-inspiratory lung volume was 100% of TLC. In conclusion, in healthy subjects exposed to MCh, a series of breaths of different depth up to TLC caused a progressive and sustained attenuation of bronchoconstriction. The effects of the depth of the five-breath series were more evident on the RV than on V(part), likely due to the different mechanisms that regulate airway closure and expiratory flow limitation.     

Evidence of post-pollination barriers among three colour morphs of the deceptive orchid Dactylorhiza sambucina (L.) Soó

Floral-colour polymorphism in rewardless orchids has been hypothesized to be maintained by means of naïve insects, which after visiting a flower without reward will tend to fly elsewhere, looking for a flower of a different colour. In this study, levels of male and female reproductive success were monitored in Southern Italy populations of the deceptive orchid Dactylorhiza sambucina, through field observations over 3 years. These populations were characterized by the presence of a rare pink morph which is sympatric with the more frequent yellow and red morphs. In addition, final plant fertility was evaluated through percentages of embryo-containing seeds produced in both natural conditions and hand-pollination experiments. Results showed that pollinator preferences were independent of the morph frequencies and thus do not promote the predicted negative frequency-dependent selection. Although yellow and pink morphs showed significantly higher male reproductive success (RS), we found comparable levels of female RS, which suggest that pollinator behaviour cannot be the main mechanism which maintains this polymorphism. Interestingly, we found different percentages of embryo-containing seeds in fruits set under natural conditions as well as in those obtained from experimental crosses. In particular, pink morph showed a very low intrinsic fertility. Moreover, fertility in intra- was higher than in inter-morph crosses. To our knowledge, this is the first study pointing out the occurrence in the orchid family of post-pollination reproductive barriers. Findings are discussed in light of present hypothesis on the evolution and maintenance of colour polymorphism in deceptive orchids and other angiosperms.     

Multisensory integration in the superior colliculus: a neural network model

Neurons in the superior colliculus (SC) are known to integrate stimuli of different modalities (e.g., visual and auditory) following specific properties. In this work, we present a mathematical model of the integrative response of SC neurons, in order to suggest a possible physiological mechanism underlying multisensory integration in SC. The model includes three distinct neural areas: two unimodal areas (auditory and visual) are devoted to a topological representation of external stimuli, and communicate via synaptic connections with a third downstream area (in the SC) responsible for multisensory integration. The present simulations show that the model, with a single set of parameters, can mimic various responses to different combinations of external stimuli including the inverse effectiveness, both in terms of multisensory enhancement and contrast, the existence of within- and cross-modality suppression between spatially disparate stimuli, a reduction of network settling time in response to cross-modal stimuli compared with individual stimuli. The model suggests that non-linearities in neural responses and synaptic (excitatory and inhibitory) connections can explain several aspects of multisensory integration.     

Molecular identification of mycorrhizal fungi in <Emphasis Type="Italic">Dactylorhiza sambucina</Emphasis> (Orchidaceae)

We amplified and sequenced internal transcribed spacer (ITS) region of the nuclear ribosomal repeat from fungi in roots of Dactylorhiza sambucina (Orchidaceae) and used the extended database to identify the mycorrhizal fungi. We molecularly identified three ITS recovered from D. sambucina roots, one belonging to Rhizoctonia group, and two to ascomycetes, for the first time in Orchidoidae. In many cases, two sequence types were found from the same orchid root, providing that two taxa may be involved in mycorrhizal formation (multiple mycobiont colonization). Moreover, we demonstrated that D. sambucina plants, irrespective of their colour polymorphism, possess roots containing several fungi belonging to both asco- and basidiomycetes.     

Optimization of the dilute maleic acid pretreatment of wheat straw

Background  

In this study, the dilute maleic acid pretreatment of wheat straw is optimized, using pretreatment time, temperature and maleic acid concentration as design variables. A central composite design was applied to the experimental set up. The response factors used in this study are: (1) glucose benefits from improved enzymatic digestibility of wheat straw solids; (2) xylose benefits from the solubilization of xylan to the liquid phase during the pretreatment; (3) maleic acid replenishment costs; (4) neutralization costs of pretreated material; (5) costs due to furfural production; and (6) heating costs of the input materials. For each response factor, experimental data were fitted mathematically. After data translation to €/Mg dry straw, determining the relative contribution of each response factor, an economic optimization was calculated within the limits of the design variables.