Combined effects of soil moisture and nitrogen availability variations on grass productivity in African savannas

Savannas cover about 20% of the Earth’s land area and 50% of Africa. As an indispensable component of savanna, grasses play an important role in these ecosystems. A better understanding of grass productivity and its controlling factors in savanna ecosystems could therefore be a key to understand the functioning of savannas and predict savanna responses to future climatic changes. In this study, a stable isotope fertilization experiment was conducted to determine how factors limiting grass production in savannas differ across regional climate gradients. The study was conducted on the geomorphically homogenous Kalahari Transect (KT), which offers an ideal setting to study nutrient and vegetation dynamics independently of confounding soil effects. The results show that the grasses assimilated the added fertilizer at all the sites but they did not respond to nitrogen fertilization for both dry and wet years, and at both dry and wet ends of the Transect. Although prior studies have proposed a switch between water and nitrogen limitations between arid and mesic savannas, our results suggest that nitrogen availability may not limit grass productivity across the whole KT. Thus, although the traditional classifications as nutrient poor (broad-leaf) and nutrient rich (fine-leaf) savanna ecosystems may still be useful, it does not necessarily imply the existence of nitrogen limitation in the nutrient poor area; in fact, it is more likely that the herbaceous species found in the more humid sites (nutrient poor sites) are already adapted to lower nitrogen availability.     

Caffeine and CSC,adenosine A2A antagonists,offer neuroprotection against 6-OHDA-induced neurotoxicity in rat mesencephalic cells

In this study, the cytoprotective effects of caffeine (CAF) and 8-(3-chlorostyryl)-caffeine (CSC), A_2A receptor antagonists, were tested against 6-OHDA-induced cytotoxicity, in rat mesencephalic cells. Both drugs significantly increased the number of viable cells, after their exposure to 6-OHDA, as measured by the MTT assay. While nitrite levels in the cells were drastically increased by 6-OHDA, their concentrations were brought toward normality after CAF or CSC, indicating that both drugs block 6-OHDA-induced oxidative stress which leads to free radicals generation. A complete blockade of 6-OHDA-induced lipid peroxidation, considered as a major source of DNA damage, was observed after cells treatment with CAF or CSC. 6-OHDA decreased the number of normal cells while increasing the number of apoptotic cells. In the CAF plus 6-OHDA group, a significant recover in the number of viable cells and a decrease in the number of apoptotic cells were seen, as compared to the group treated with 6-OHDA alone. A similar effect was observed after cells exposure to CSC in the presence of 6-OHDA. Unexpectedly, while a significant lower number of activated microglia was observed after cells exposure to CAF plus 6-OHDA, this was not the case after cells exposure to CSC under the same conditions. While CAF lowered the percentage of reactive astrocytes increased by 6-OHDA, CSC presented no effect. The effects of these drugs were also examined on the releases of myeloperoxidase (MPO), an inflammatory marker, and lactate dehydrogenase (LDH), a marker for cytotoxicity, in human neutrophils, in vitro. CSC and CAF (0.1, 1 and 10 μg/ml) produced inhibitions of the MPO release from PMA-stimulated cells, ranging from 45 to 83%. In addition, CSC and CAF (5, 50 and 100 μg/ml) did not show any cytotoxicity in the range of concentrations used, as determined by the LDH assay. All together, our results showed a strong neuroptrotection afforded by caffeine or CSC, on rat mesencephalic cells exposed to 6-OHDA. Furthermore, CSC and caffeine actions, inhibiting MPO as well as LDH releases, would contribute to their possible benefit in the treatment of neurodegenerative diseases, including DP. These effects are partially due to the ability of these A_2A antagonists to decrease the cells free radicals production and oxidative stress, that are major components of 6-OHDA-induced cytotoxicity.     

Chemical constituents of Papulaspora immersa, an endophyte from Smallanthus sonchifolius (Asteraceae), and their cytotoxic activity

Papulaspora immersa H. H. Hotson was isolated from roots and leaves of Smallanthus sonchifolius (Poepp. and Endl. ) H. Rob. (Asteraceae), traditionally known as Yacon. The fungus was cultured in rice, and, from the AcOEt fraction, 14 compounds were isolated. Among them, (22E,24R)‐8,14‐epoxyergosta‐4,22‐diene‐3,6‐dione ( 4 ), 2,3‐epoxy‐1,2,3,4‐tetrahydronaphthalene‐c‐1,c‐4,8‐triol ( 10 ), and the chromone papulasporin ( 13 ) were new secondary metabolites. The spectral data of the known natural products were compared with the literature data, and their structures were established as the (24R)‐stigmast‐4‐en‐3‐one ( 1 ), 24‐methylenecycloartan‐3β‐ol ( 2 ), (22E,24R)‐ergosta‐4,6,8(14),22‐tetraen‐3‐one ( 3 ), (?)‐(3R,4R)‐4‐hydroxymellein ( 5 ), (?)‐(3R)‐5‐hydroxymellein ( 6 ), 6,8‐dihydroxy‐3‐methylisocoumarin ( 7 ), (?)‐(4S)‐4,8‐dihydroxy‐α‐tetralone ( 8 ), naphthalene‐1,8‐diol ( 9 ), 6,7,8‐trihydroxy‐3‐methylisocoumarin ( 11 ), 7‐hydroxy‐2,5‐dimethylchromone ( 12 ), and tyrosol ( 14 ). Compound 4 showed the highest cytotoxic activity against the human tumor cell lines MDA‐MB435 (melanoma), HCT‐8 (colon), SF295 (glioblastoma), and HL‐60 (promyelocytic leukemia), with IC₅₀ values of 3.3, 14.7, 5.0 and 1.6 μM , respectively. Strong synergistic effects were also observed with compound 5 and some of the isolated steroidal compounds.     

Non-Polar Chemical Constituents of Atemoya and Evaluation of the Cytotoxic and Antimicrobial Activity

This study aimed to identify the chemical composition of essential oil from fruits (EOAF) and the hexanic crude extract from aerial parts (At-Hex) of atemoya (Annona cherimola x Annona squamosa), a hybrid belonging to the Annonaceae family. Cytotoxic and antimicrobial activity was also evaluated. OEAF was obtained by hydrodistillation using a Clevenger apparatus, and their composition was analyzed by gas chromatography-mass spectrometry (GC-MS) analyses. Cytotoxicity was tested against human tumor cell lines HCT-116 (colon carcinoma), SF-295 (glioblastoma), OVCAR-8 (ovarian carcinoma) and HL60 (leukemia) using 3-(4,5-dimethyl-2-thiazolyl)-2,5- diphenyl-2H-tetrazolium bromide (MTT) assay, while antimicrobial activity was conducted by bioauthography method against eleven microorganisms strains. Twenty-four compounds were identified in the EOAF and twenty-nine in At-Hex. The monoterpenes linalool (25.70%), α-pinene (10.38%), β-pinene (9.12%), transocimene (7.43%), and the sesquiterpene bicyclogermacrene (12.58%) were the major constituents of EOAF, whereas the sesquiterpene spathulenol (13.91%) was the main compound of At-Hex. At-Hex showed a high cytotoxicity against SF-295 (glioblastoma). These findings show an important chemotaxonomic contribution for the Annonaceae family, mainly for the Annona genus. Atemoya proved to be a promising source of substances with potential cytotoxic activity.     

Guanidine Alkaloids from Monanchora arbuscula: Chemistry and Antitumor Potential

Five guanidine alkaloids, mirabilin B ( 1 ), 8bβ‐hydroxyptilocaulin ( 2 ), ptilocaulin ( 3 ), and a mixture of the 8β‐ and 8α‐epimers, 4 and 5 , of 8‐hydroxymirabilin (1,8a;8b,3a‐didehydro‐8‐hydroxyptilocaulin), were isolated from Monanchora arbuscula colonies collected off the northeastern Brazilian coast. All structures were elucidated by spectroscopic analysis, including 1D (¹H‐, ¹³C‐ (BB), and ¹³C‐DEPT) and 2D (COSY, HSQC, and HMBC) NMR experiments, and comparison with the literature data. The cytotoxicity of the isolated compounds were evaluated against four tumor cell lines, showing that mirabilin B ( 1 ) and the two epimers were inactive, while 8bβ‐hydroxyptilocaulin ( 2 ) and ptilocaulin ( 3 ) presented IC₅₀ values in the range of 7.9 to 61.5 μM , and 5.8 to 40.0 μM , respectively. Further studies on the mechanism of action of ptilocaulin, using HL‐60 leukemia cells, demonstrated that this guanidine compound induced apoptosis of the treated cells.     

Precursors of state transitions in stochastic systems with delay

Ecosystem dynamics may exhibit alternative stable states induced by positive feedbacks between the state of the system and environmental drivers. Bistable systems are prone to abrupt shifts from one state to another in response to even small and gradual changes in external drivers. These transitions are often catastrophic and difficult to predict by analyzing the mean state of the system. Indicators of the imminent occurrence of phase transitions can serve as important tools to warn ecosystem managers about an imminent transition before the bifurcation point is actually reached. Thus, leading indicators of phase transitions can be used either to prepare for or to prevent the occurrence of a shift to the other state. In recent years, theories of leading indicators of ecosystem shift have been developed and applied to a variety of ecological models and geophysical time series. It is unclear, however, how some of these indicators would perform in the case of systems with a delay. Here, we develop a theoretical framework for the investigation of precursors of state shift in the presence of drivers acting with a delay. We discuss how the effectiveness of leading indicators of state shift based on rising variance may be affected by the presence of delays. We apply this framework to an ecological model of desertification in arid grasslands.     

PROgnosticating COeliac patieNts SUrvivaL: The PROCONSUL Score

Introduction

It has been shown that mortality rates of coeliac patients correlate with age at diagnosis of coeliac disease, diagnostic delay for coeliac disease, pattern of clinical presentation and HLA typing. Our aim was to create a tool that identifies coeliac patients at higher risk of developing complications.

Methods

To identify predictors of complications in patients with coeliac disease, we organised an observational multicenter case-control study based on a retrospective collection of clinical data. Clinical data from 116 cases (patients with complicated coeliac disease) and 181 controls (coeliac patients without any complications) were collected from seven European centres. For each case, one or two controls, matched to cases according to the year of assessment, gender and age, were selected. Diagnostic delay, pattern of clinical presentation, HLA typing and age at diagnosis were used as predictors.

Results

Differences between cases and controls were detected for diagnostic delay and classical presentation. Conditional logistic models based on these statistically different predictors allowed the development of a score system. Tertiles analysis showed a relationship between score and risk of developing complications.

Discussion

A score that shows the risk of a newly diagnosed coeliac patient developing complications was devised for the first time. This will make it possible to set up the follow-up of coeliac patients with great benefits not only for their health but also for management of economic resources.

Conclusions

We think that our results are very encouraging and represent the first attempt to build a prognostic score for coeliac patients.     

Effects of competition on induction of crassulacean acid metabolism in a facultative CAM plant

Abiotic drivers of environmental stress have been found to induce CAM expression (nocturnal carboxylation) in facultative CAM species such as Mesembryanthemum crystallinum. The role played by biotic factors such as competition with non-CAM species in affecting CAM expression, however, remains largely understudied. This research investigated the effects of salt and water conditions on the competition between M. crystallinum and the C₃ grass Bromus mollis with which it is found to coexist in California’s coastal grasslands. We also investigated the extent to which CAM expression in M. crystallinum was affected by the intensity of the competition with B. mollis. We found that M. crystallinum had a competitive advantage over B. mollis in drought and saline conditions, while B. mollis exerted strong competitive effects on M. crystallinum in access to light and soil nutrients in high water conditions. This strong competitive effect even outweighed the favorable effects of salt or water additions in increasing the biomass and productivity of M. crystallinum in mixture. Regardless of salt conditions, M. crystallinum did not switch to CAM photosynthesis in response to this strong competitive effect from B. mollis. Disturbance (i.e., grass cutting) reduced the competitive pressure by B. mollis and allowed for CAM expression in M. crystallinum when it was grown mixed with B. mollis. We suggest that moderate competition with other functional groups can enhance CAM expression in M. crystallinum, thereby affecting its plasticity and ability to cope with biological stress.