Glutathione homeostasis and Cd tolerance in the Arabidopsis sultr1;1-sultr1;2 double mutant with limiting sulfate supply.

KEY MESSAGE: Cadmium sensitivity in sultr1;1 - sultr1;2 double mutant with limiting sulfate supply is attributed to the decreased glutathione content that affected oxidative defense but not phytochelatins' synthesis. In plants, glutathione (GSH) homeostasis plays pivotal role in cadmium (Cd) detoxification. GSH is synthesized by sulfur (S) assimilation pathway. Many studies have tried to investigate the role of GSH homeostasis on Cd tolerance using mutants; however, most of them have focused on the last few steps of S assimilation. Until now, mutant evidence that explored the relationship between GSH homeostasis on Cd tolerance and S absorption is rare. To further reveal the role of GSH homeostasis on Cd stress, the wild-type and a sultr1;1-sultr1;2 double mutant which had a defect in two distinct high-affinity sulfate transporters were used in this study. Growth parameters, biochemical or zymological indexes and S assimilation-related genes' expression were compared between the mutant and wild-type Arabidopsis plants. It was found that the mutations of SULTR1;1 and SULTR1;2 did not affect Cd accumulation. Compared to the wild-type, the double mutant was more sensitive to Cd under limited sulfate supply and suffered from stronger oxidative damage. More importantly, under the same condition, lower capacity of S assimilation resulted in decreased GSH content in mutant. Faced to the limited GSH accumulation, mutant seedlings consumed a large majority of GSH in pool for the synthesis of phytochelatins rather than participating in the antioxidative defense. Therefore, homeostasis of GSH, imbalance between antioxidative defense and severe oxidative damage led to hypersensitivity of double mutant to Cd under limited sulfate supply.

Competition and coexistence in regional habitats.

Habitat heterogeneity plays a key role in the dynamics and structures of communities. In this article, a two-species metapopulation model that includes local competitive dynamics is analyzed to study the population dynamics of two competing species in spatially structured habitats. When local stochastic extinction can be ignored, there are, as in Lotka-Volterra equations, four outcomes of interspecific competition in this model. The outcomes of competition depend on the competitive intensity between the competing pairs. An inferior competitor and a superior competitor, or two strongly competing species, can never stably coexist, whereas two weak competitors (even if they are very similar species) may coexist over the long term in such environments. Local stochastic extinction may greatly affect the outcomes of interspecific competition. Two competing species can or cannot stably coexist depending not only on the competitive intensity between the competing pairs but also on their precompetitive distributions. Two weak competitors that have similar precompetitive distributions can always regionally coexist. Two strongly competing species that competitively exclude each other in more stable habitats may be able to stably coexist in highly heterogenous environments if they have similar precompetitive distributions. There is also a chance for an inferior competitor to coexist regionally or even to exclude a superior competitor when the superior competitor has a narrow precompetitive distribution and the inferior competitor has a wide precompetitive distribution.

Effect of yessotoxin on cytosolic calcium levels in human hepatocellular carcinoma cells in vitro.

Yessotoxin (YTX) and its analogs are a type of marine toxins found in marine environments in numerous coastal countries. These toxins tend to accumulate in filter-feeding molluscs and may threaten the shellfish industry and public health. Several previous studies indicated that YTX may induce apoptosis in different types of cell lines, although the exact underlying mechanisms have not yet been elucidated. The aim of this study was to mainly focus on the effect of YTX on cytosolic Ca2+ levels in human hepatocellular carcinoma cells. In order to investigate the exact mechanism of YTX-evoked Ca2+ increase, laser scanning confocal microscopy was used, with the addition of the chelator ethylene glycol tetraacetic acid (EGTA) and nifedipine, an L-type Ca2+ channel blocker, to the reaction system. The results demonstrated that YTX caused cytosolic Ca2+ level increase in Bel7402 cells and the YTX-evoked Ca2+ increase was successfully blocked by EGTA and nifedipine. Therefore, our results indicated that YTX may cause apoptosis via inducing Ca2+ entry in Bel7402 cells.

Yessotoxin induces apoptosis in HL7702 human liver cells.

The marine toxin yessotoxin (YTX) is found in numerous aquatic environments and poses a potential threat to the shellfish industry and to public health. We analyzed the toxicity of YTX on HL7702 human liver cells using optical microscopy, Hoechst 33342 chromatin staining, DNA gel electrophoresis, rhodamine 123 staining and calcium-sensitive laser scanning confocal microscopy. The results demonstrated that YTX induced the usual hallmarks of apoptosis, including chromatin condensation, DNA laddering, activity of caspase-3 deregulation and loss of mitochondrial membrane potential. Furthermore, YTX caused cytosolic calcium levels to increase in HL7702 cells. YTX may cause liver damage through hepatocyte apoptosis.

Characterization of apoptotic changes induced by yessotoxin in the Bel7402 human hepatoma cell line.

The apoptotic effects of yessotoxin (YTX) on Bel7402 human hepatoma cells have been evaluated by the combination of several methods, including optical microscopy, Hoechst 33342 staining and DNA gel electrophoresis. Rhodamine 123 staining has also been used to investigate changes in mitochondrial transmembrane potential. The results indicated that YTX has negative effects on human liver cells and induces apoptosis. Furthermore, changes in calcium concentrations were analyzed using the fluorescence probe Fluo-3 AM. The results showed that intracellular calcium concentrations increased after treatment with YTX.

Generation of the CF3 radical from trifluoromethylsulfonium triflate and its trifluoromethylation of styrenes.

The CF(3) radical was generated from the reaction of S-(trifluoromethyl)diphenylsulfonium triflate with Na(2)S(2)O(4) or HOCH(2)SO(2)Na under suitable conditions without further reduction. Based on this, a method for the synthesis of α-trifluoromethylated ketones has been successfully developed.

[Increasing pattern of phytoplankton biomass with species richness and tests of sampling and complementary effects].

A total of eighteen common phytoplankton species in China coastal waters were divided into different assemblages to investigate the increasing pattern of the assemblage biomass with species richness. The sampling effect was studied by multiple analysis of variance (MANOVA) method, and the complementary effect was explored by over-yielding analysis, relative yield total (RYT) index, and subset approach. It was shown that the increasing pattern of assemblage biomass with species richness was not unitary. When the species number was lower than 5, the assemblage biomass increased with increasing species richness; when the species number was higher than 5, there were no obvious relationships between assemblage biomass and species richness. A stronger complementary effect was observed inside the assemblage, presenting a hump-shaped variation with increasing species richness. The sampling effect of the assemblages occurred at stable growth phase.

Apoptosis induced by yessotoxins in Hela human cervical cancer cells in vitro.

To investigate the apoptotic effects of an extract of red-tide algae, Protoceratium reticulatum, on HeLa cells, we used liquid chromatography-tandem mass spectrometry, optical microscopy, Hoechst 33342/propidine iodide staining, and DNA gel electrophoresis to analyze its constituents and toxicity, as well as rhodamine 123 staining to investigate changes in mitochondrial membrane potential. Analysis showed that the P. reticulatum extract contained the yessotoxins (YTXs) homo-YTX, 45-OH-YTX and 45-OH-homo-YTX. The results indicated that P. reticulatum extract negatively influences HeLa cells and induces their apoptosis.

[Effects of species richness on colony biomass and tests of sampling- and complementary effect].

With eight species of unicellular algae cultured in random combinations to construct the assemblages with different degrees of richness, the increase pattern of colony biomass with the change of species richness was investigated, and the sampling effect was detected by using multiple variance analysis (MANOVA) method. Three analysis methods, i. e., over-yielding analysis, relative yield total (RYT) index, and subset approach, were applied to explore the complementary effect, and additive partitioning method was applied to separate the sampling effect and complementary effect quantitatively. The results showed that the colony biomass presented a saturated rise with the increase of species richness, and a strong complementary effect was observed in phytoplankton colonies. At exponential growth phase, some specific algal species affected the colony biomass significantly, but after reaching the stable phase, the biomass was not affected by the presence of given phytoplankton. The sampling effect was generally negative at stable phase, while the complementary effect and net biodiversity effect were always positive.