Modulation of the Photosynthetic Source:Sink Relationship in Cultures of the Cyanobacterium Nostoc Rivulare

Nostoc rivulare was grown in batch cultures under controlled CO₂ and NO₃ ^– concentrations to modulate the photosynthetic source:sink relationship. Increasing CO₂ supply accelerated the accumulation of chlorophyll (Chl) a, i.e., supplemental CO₂ combined with double concentrations of NO₃ ^– more than doubled the amounts of Chl a relative to those of the original medium. Photosynthetic oxygen evolution and respiratory oxygen uptake were both enhanced by elevated CO₂ and NO₃ ^–. Contents of soluble sugars and starch (total non-structural saccharides) as well as insoluble saccharides (structural fraction) were affected by altering CO₂-NO₃ ^– combinations. Uptake as well as reduction of either NO₃ ^– or NO₂ ^– was inhibited by CO₂ deprivation. Expanding the sink size via increasing NO₃ ^– supply enhanced photosynthesis and thus the sink (NO₃ ^–) acted as a feed forward stimulator of the source (photosynthesis). The regulatory role of nitrate on photosynthesis was most influential in CO₂-deprived cultures since it could enhance photosynthesis to higher levels than CO₂-supplemented, nitrate-free cultures.     

Quaternary sandstones, northeast Jordan: Age, depositional environments and climatic implications

OSL dating of weakly consolidated, root-bound, non-calcareous quartz arenites in northeast Jordan, currently assigned to the Plio-Pleistocene Azraq Formation, suggests a Middle Pleistocene (652 ± 47 ka) age. The sandstones are up to 15.5 m thick and overlain by a 2.5 m thick Holocene gypcrete caprock. Facies and textural analyses suggest that the sandstones are predominantly aeolian in origin, mainly derived from Tertiary sediments exposed close to the depositional site. The sands were transported by the prevailing NW winds and deposited in a broad, relatively flat sand sheet environment. Rhizoliths occur throughout the sandstones, mainly as long, downward tapering, vertical tap roots, rarely branched and with few laterals. Microscopic examination of root cores replaced by carbonate reveals the presence of alveolar fabrics, possible needle fibre calcite, calcified organic filaments of fungal, root vessel and root hair origins, characteristic of low magnesium beta calcretes, typical of humid climates.Morphologically the roots resemble modern shrub-like species typical of desert environments where water availability at the surface and in the subsurface was sufficient to support an effective vegetation cover. Plots of stratigraphic variations in root length, root spacing and root frequency reflect temporal variations in the water table level and precipitation during sand deposition. All three parameters show a similar crude cyclicity consistent with fluctuations in the level of the water table with the most moist phase beneath the predominantly waterlain Holocene gypcrete when trees appeared for the first time. The gypcrete signifies a change to temporary wetter conditions and may mark the boundary between the Pleistocene and Holocene in this area. Although pedogenic horizonation is poorly developed, especially in desert sands, the beta calcretes and rhizocretions typically form within active soil zones. Soils do not form where rainfall is < 150 mm per year, and above 350 mm complete leaching of the edaphon occurs. However, above 300 mm per year shrubs are replaced by grassland, hence rainfall is inferred to have been 150-300 mm per year, much higher than the < 50 mm in the area today. The age of the sandstones may correlate with isotopic event 17, dated at 659 ka, when the Pleistocene climate in Jordan was characterised by arid to semi-arid phases interrupted by shorter more humid phases, when the water table was higher and the precipitation/evaporation balance greater than today.     

Influence of neighbouring companion plants on the performance of aphid populations on sweet pepper plants under greenhouse conditions

相似文献   

Azoospermias au Sénégal: quelle prise en charge à l’heure de l’ICSI?

Objective

to determine the place of azoospermia among the various causes of infertility in Senegal.

Material and methods

141 cases of azoospermia were identified from a series of 492 infertile patients. The clinical profile, laboratory results and outcome after management were studied.

Results

The mean age was 40.6 years. Testicular atrophy was detected in 34.75% of cases. Azoospermia was secretory in 71.69% of cases. A varicocele was associated in 56% of cases. Varicocele repair was performed in 32.62% and allowed an improvement of sperm parameters in 28.3% of cases. Testicular biopsy, performed in 53 cases, demonstrated 2 cases of Sertoli cell syndrome, 3 cases of arrested maturation, 8 cases of hypo spermatogenesis, and 25 cases of seminiferous tubules. Forty nine cases of azoospermia were associated with normal FSH levels. Only one patient was treated by assisted reproductive technologies (ART).     

Influence of selenium on toxicity of some heavy metals in the green alga Scenedesmus obliquus

The green alga Scenedesmus obliquus was incubated with various heavy metals (Cd2+, Zn2+, Mn2+, Ni2+) in presence/absence of selenium. S. obliquus exhibited higher rates of growth and some metabolic activities in cultures containing 0.1 mM Se than those containing only the heavy metals. The positive effect of Se was found in presence of Cd2+ while that in the case of presence of Ni2+ was less pronounced.     

Biosynthetically directed fractional 13C labeling facilitates identification of Phe and Tyr aromatic signals in proteins

Analysis of 2D [¹³C,¹H]-HSQC spectra of biosynthetic fractionally ¹³C labeled proteins is a reliable, straightforward means to obtain stereospecific assignments of Val and Leu methyl sites in proteins. Herein we show that the same fractionally labeled protein sample facilitates observation and identification of Phe and Tyr aromatic signals. This is the case, in part, because the fractional ¹³C labeling yields aromatic rings in which some of the ¹³C-¹³C J-couplings, present in uniformly labeled samples, are absent. Also, the number of homonuclear J-coupling partners differs for the -, - and -carbons. This enabled us to vary their signal intensities in distinctly different ways by appropriately setting the ¹³C constant-time period in 2D [¹³C,¹H]-HSQC spectra. We illustrate the application of this approach to an 18 kDa protein, c-VIAF, a modulator of apoptosis. In addition, we show that cancellation of the aromatic ¹³C CSA and ¹³C-¹H dipolar interactions can be fruitfully utilized in the case of the fractionally labeled sample to obtain high resolution ¹³C constant-time spectra with good sensitivity.     

Elementary mechanisms producing facilitation of Cav2.1 (P/Q-type) channels

The regulation of Ca(V)2.1 (P/Q-type) channels by calmodulin (CaM) showcases the powerful Ca(2+) decoding capabilities of CaM in complex with the family of Ca(V)1-2 Ca(2+) channels. Throughout this family, CaM does not simply exert a binary on/off regulatory effect; rather, Ca(2+) binding to either the C- or N-terminal lobe of CaM alone can selectively trigger a distinct form of channel modulation. Additionally, Ca(2+) binding to the C-terminal lobe triggers regulation that appears preferentially responsive to local Ca(2+) influx through the channel to which CaM is attached (local Ca(2+) preference), whereas Ca(2+) binding to the N-terminal lobe triggers modulation that favors activation via Ca(2+) entry through channels at a distance (global Ca(2+) preference). Ca(V)2.1 channels fully exemplify these features; Ca(2+) binding to the C-terminal lobe induces Ca(2+)-dependent facilitation of opening (CDF), whereas the N-terminal lobe yields Ca(2+)-dependent inactivation of opening (CDI). In mitigation of these interesting indications, support for this local/global Ca(2+) selectivity has been based upon indirect inferences from macroscopic recordings of numerous channels. Nagging uncertainty has also remained as to whether CDF represents a relief of basal inhibition of channel open probability (P(o)) in the presence of external Ca(2+), or an actual enhancement of P(o) over a normal baseline seen with Ba(2+) as the charge carrier. To address these issues, we undertake the first extensive single-channel analysis of Ca(V)2.1 channels with Ca(2+) as charge carrier. A key outcome is that CDF persists at this level, while CDI is entirely lacking. This result directly upholds the local/global Ca(2+) preference of the lobes of CaM, because only a local (but not global) Ca(2+) signal is here present. Furthermore, direct single-channel determinations of P(o) and kinetic simulations demonstrate that CDF represents a genuine enhancement of open probability, without appreciable change of activation kinetics. This enhanced-opening mechanism suggests that the CDF evoked during action-potential trains would produce not only larger, but longer-lasting Ca(2+) responses, an outcome with potential ramifications for short-term synaptic plasticity.     

Generalizing causal inferences from individuals in randomized trials to all trial‐eligible individuals

We consider methods for causal inference in randomized trials nested within cohorts of trial‐eligible individuals, including those who are not randomized. We show how baseline covariate data from the entire cohort, and treatment and outcome data only from randomized individuals, can be used to identify potential (counterfactual) outcome means and average treatment effects in the target population of all eligible individuals. We review identifiability conditions, propose estimators, and assess the estimators' finite‐sample performance in simulation studies. As an illustration, we apply the estimators in a trial nested within a cohort of trial‐eligible individuals to compare coronary artery bypass grafting surgery plus medical therapy vs. medical therapy alone for chronic coronary artery disease.