The Effects of Interannual Rainfall Variability on Tree–Grass Composition Along Kalahari Rainfall Gradient

Precipitation variability has been predicted to increase in a global warmer climate, and is expected to greatly affect plant growth, interspecies interactions, plant community composition, and other ecosystem processes. Although previous studies have investigated the effect of intra-annual rainfall variability on plant growth and ecosystem dynamics, the impacts of interannual rainfall variability remain understudied. This paper uses satellite data and develops a new mechanistic model to investigate the response of tree–grass composition to increasing interannual rainfall variability in arid to sub-humid ecosystems along the Kalahari Transect in Southern Africa. Both satellite data and model results show that increasing interannual rainfall fluctuations favor deep-rooted trees over shallow-rooted grasses in drier environments (that is, mean annual rainfall, MAP < 900–1000 mm) but favor grasses over trees in wetter environments (that is, MAP > 900–1000 mm). Trees have a competitive advantage over grasses in dry environments because their generally deeper root systems allow them to have exclusive access to the increased deep soil water resources expected to occur in wet years as a result of the stronger interannual rainfall fluctuations. In relatively wet environments, grasses are favored because of their high growth rate that allows them to take advantage of the window of opportunity existing in years with above average precipitation and thus increase fire-induced tree mortality. Thus, under increasing interannual rainfall fluctuations both direct effects on soil water availability and indirect effects mediated by tree–grass interactions and fire dynamics are expected to play an important role in determining changes in plant community composition.     

Cytotoxic abietane diterpenes from Hyptis martiusii Benth

From roots of Hyptis martiusii Benth. two tanshinone diterpenes were isolated, the new 7beta-hydroxy-11,14-dioxoabieta-8,12-diene (1) in addition to the known 7alpha-acetoxy-12-hydroxy-11,14-dioxoabieta-8,12-diene (7alpha-acetoxyroyleanone) (2). Structures of 1 and 2 were established by spectroscopic means. The cytotoxic activity against five cancer cell lines was evaluated. Compounds 1 and 2 displayed considerable cytotoxic activity against several cancer cell lines with IC50 values in the range of 3.1 to 11.5 microg/ml and 0.9 to 7.6 microg/ml, respectively. The cytotoxic activity seemed to be related to inhibition of DNA synthesis, as revealed by the reduction of 5-bromo-2'-deoxyuridine incorporation and induction of apoptosis, as indicated by the acridine orange/ethidium bromide assay and morphological changes after 24 h of incubation in leukemic cells.     

Studies on the cytotoxicity of cucurbitacins isolated from Cayaponia racemosa (Cucurbitaceae)

The cytotoxic potential of three cucurbitacins, 2,3,16,20(R),25-pentahydroxy-11,22-dioxo-cucurbita-5-en (cucurbitacin P, 1), 2,3,16,20(R),25-pentahydroxy-22-oxocucurbita-5-en (2) and 2,3,16,20(R),25-pentahydroxy-22-oxocucurbita-5,23(E)-diene (deacetylpicracin, 3), obtained from Cayaponia racemosa was evaluated as their ability to induce brine shrimp lethality, to inhibit the development of sea urchin eggs and tumor cell proliferation, and to lysis mouse erythrocytes. Compounds 1 and 2 were highly toxic with LC50 of (29.6+/-.1) (56.8) and (38.8 +/-.0) (76.6) micro/mL (umicro), respectively, while compound 3 was not effective at the tested concentrations. All tested compounds possessed an inhibitory effect on the proliferation of tumor cell lines, compound 1 being the most active, followed by 2 and 3. Nevertheless, no hemolytic activity or inhibition of the development of sea urchin eggs was observed for these compounds.     

Studies on the cytotoxic activity of synthetic 2H-azirine-2-azetidinone compounds

2-Azetidinones and 2H-azirines show antibacterial and cytotoxic activities, however the biological properties of molecules containing both 2H-azirine and 2-azetidinone functions in the same structure had never been evaluated before. In the present study, two 2H-azirine-2-azetidinones (1 and 2) and three 2H-azirines (3-5) were synthesized from 2-formyl-3-phenyl-2H-azirine-N-arylimines with diphenylketene. The compounds were assayed for antibacterial and cytotoxic activities. None of them showed antibacterial activity on the tested strains, but both 2H-azirine-2-azetidinones showed cytotoxicity against four tumor cell lines (HL-60, leukemia; HCT-8, colon cancer; MDA-MB-435, melanoma; and SF-295, CNS). The IC₅₀ values of 1 ranged from 1.1 to 10.5 μM and from 3.8 to 26.6 μM for 2. The mechanism of cell growth inhibition of 1 and 2 towards HL-60 cell line was also investigated. Membrane damage, cell viability, DNA synthesis inhibition and morphological changes were evaluated. The preliminary findings suggested that 1 and 2 induce apoptosis.     

Pro-apoptotic activity of lipidic α-amino acids isolated from Protopalythoa variabilis

Lipidic α-amino acids (LAAs) have been described as non-natural amino acids with long saturated or unsaturated aliphatic chains. In the continuing prospect to discover anticancer agents from marine sources, we have obtained a mixture of two cytotoxic LAAs (1a and 1b) from the zoanthid Protopalythoa variabilis. The anti-proliferative potential of 14 synthetic LAAs and 1a/1b were evaluated on four tumor cell lines (HCT-8, SF-295, MDA-MB-435, and HL-60). Five of the synthetic LAAs showed high percentage of tumor cell inhibition, while 1a/1b completely inhibited tumor cell growth. Additionally, apoptotic effects of 1a/1b were studied on HL-60 cell line. 1a/1b-treated cells showed apoptosis morphology, loss of mitochondrial potential, and DNA fragmentation.     

Synthetic Chalcone Derivatives as Inhibitors of Cathepsins K and B,and Their Cytotoxic Evaluation

A series of chalcone derivatives, 1 – 15 , were prepared by Claisen? Schmidt condensation and evaluated for their cytotoxicities on tumor cell lines and also against proteolytic enzymes such as cathepsins B and K. Of the compounds synthesized, (E)‐3‐(3,4‐dimethoxyphenyl)‐1‐phenylprop‐2‐en‐1‐one ( 12 ), (E)‐3‐(4‐chlorophenyl)‐1‐phenylprop‐2‐en‐1‐one ( 13 ), (E)‐3‐(4‐methoxyphenyl)‐1‐phenylprop‐2‐en‐1‐one ( 14 ), and (E)‐3‐(4‐nitrophenyl)‐1‐phenylprop‐2‐en‐1‐one ( 15 ) showed significant cytotoxicities. The most effective compound was 15 , which showed high cytotoxic activity with an IC₅₀ value lower than 1 μg/ml, and no selectivity on the tumor cells evaluated. Substituents at C(4) of ring B were found to be essential for cytotoxicity. In addition, it was also demonstrated that some of these chalcones are moderate inhibitors of cathepsin K and have no activity against cathepsin B.     

Relationship between oviposition,virulence gene expression and parasitism success in <Emphasis Type="Italic">Cotesia typhae</Emphasis> nov. sp. parasitoid strains

Studying mechanisms that drive host adaptation in parasitoids is crucial for the efficient use of parasitoids in biocontrol programs. Cotesia typhae nov. sp. (Fernández-Triana) (Hymenoptera: Braconidae) is a newly described parasitoid of the Mediterranean corn borer Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae). Braconidae are known for their domesticated bracovirus, which is injected with eggs in the host larva to overcome its resistance. In this context, we compared reproductive success traits of four Kenyan strains of C. typhae on a French and a Kenyan populations of its host. Differences were found between the four strains and the two most contrasted ones were studied more thoroughly on the French host population. Parasitoid offspring size was correlated with parasitism success and the expression of bracovirus virulence genes (CrV1 and Cystatin) in the host larva after parasitism. Hybrids between these two parasitoid strains showed phenotype and gene expression profiles similar to the most successful parental strain, suggesting the involvement of dominant alleles in the reproductive traits. Ovary dissections revealed that the most successful strain injected more eggs in a single host larva than the less successful one, despite an equal initial ovocyte number in ovaries. It can be expected that the amount of viral particles increase with the number of eggs injected. The ability to bypass the resistance of the allopatric host may in consequence be related to the oviposition behaviour (eggs allocation). The influence of the number of injected eggs on parasitism success and on virulence gene expression was evaluated by oviposition interruption experiments.     

Cytotoxic activity of a dichloromethane extract and fractions obtained from Eudistoma vannamei (Tunicata: Ascidiacea)

This study consists of the bioassay-guided fractionation of the dichloromethane extract from Eudistoma vannamei and the pharmacological characterization of the active fractions. The dried hydromethanolic extract dissolved in aqueous methanol was partitioned with dichloromethane and chromatographed on a silica gel flash column. The anti-proliferative effect was monitored by the MTT assay. Four of the latest fractions, numbered 14 to 17, which held many chemical similarities amongst each other, were found to be the most active. The selected fractions were tested for viability, proliferation and death induction on cultures of HL-60 promyeloblastic leukemia cells. The results suggested that the observed cytotoxicity is related to apoptosis induction.     

Antileukemic effects of Didemnum psammatodes (Tunicata: Ascidiacea) constituents

Chemical investigation of the methanolic extract of the ascidian Didemnum psammatodes has led to the identification of fourteen known compounds: three methyl esters (methyl myristate, methyl palmitate and methyl stearate), four steroids (cholesterol, campesterol, stigmasterol and beta-sitosterol), two fatty acids (palmitic acid and stearic acid), three glyceryl ethers {(1,2-propanediol, 3-(heptadecyloxy), batyl alcohol and 1,2-propanediol, 3-[(methyloctadecyl)oxy]} and two nucleosides (thymidine and 2'-deoxyguanosine). Their structures were proposed by NMR and comparison with literature data and GC analysis in comparison with authentic sample. The cytotoxic activity of these compounds was evaluated against human leukemia cell line panel using the MTT assay. The mixture of the three methyl esters was the most active group of compounds, showing antiproliferative and cytotoxic effects. Further studies on their mode of action suggest that these activities are connected with inhibition of DNA synthesis and induction of both necrosis and apoptosis.