Insights into the toxicity mechanism of and cell response to the herbicide 2,4-D in plants

Although structurally similar to the natural plant hormone indol-3- acetic acid, auxin herbicides were developed for purposes other than growth, and have been successfully used in agriculture for the last 60 years. Concerted efforts are being made to understand and decipher the precise mechanism of action of IAA and synthetic auxins. Innumerable results need to be interconnected to resolve the puzzle of auxin biology and action mode of auxin herbicides. To date, different breakthroughs are providing more insights into the process of plant-herbicide interactions. Here we highlight some of the latest findings on how the 2,4-dichlorophenoxyacetic acid damages susceptible broadleaf plants, emphasizing the role of ROS as a downstream component of the auxin signal transduction under herbicide treatment.     

Effects of hypochlorite disinfection on the response of barley aleurone layers to gibberellic acid

Although the use of hypochlorite to disinfect seeds is widespread, the effects on tissues isolated from them have been largely ignored. Disinfection of barley ( Hordeum vulgare L. cv. Himalaya) half-seeds with hypochlorite solutions of ≥1.0% (w/v) available chlorine caused the pericarp to separate from the underlying tissues. Aleurone layers isolated from these grains had lower rates of oxygen consumption and released significantly less protein, PO₄³⁻ Mg²⁺, K⁺ and amylase (EC 3.2.1.1) into the medium in response to gibberellic acid (GA₃) than layers isolated from grains disinfected with a 0.1% hypochlorite solution. Disinfection with 1.0% hypochlorite also quantitatively altered the spectrum of proteins released into the incubation medium by the layers in response to GA₃.     

Protistan microbial observatory in the Cariaco Basin,Caribbean. I. Pyrosequencing vs Sanger insights into species richness

Microbial diversity and distribution are topics of intensive research. In two companion papers in this issue, we describe the results of the Cariaco Microbial Observatory (Caribbean Sea, Venezuela). The Basin contains the largest body of marine anoxic water, and presents an opportunity to study protistan communities across biogeochemical gradients. In the first paper, we survey 18S ribosomal RNA (rRNA) gene sequence diversity using both Sanger- and pyrosequencing-based approaches, employing multiple PCR primers, and state-of-the-art statistical analyses to estimate microbial richness missed by the survey. Sampling the Basin at three stations, in two seasons, and at four depths with distinct biogeochemical regimes, we obtained the largest, and arguably the least biased collection of over 6000 nearly full-length protistan rRNA gene sequences from a given oceanographic regime to date, and over 80 000 pyrosequencing tags. These represent all major and many minor protistan taxa, at frequencies globally similar between the two sequence collections. This large data set provided, via the recently developed parametric modeling, the first statistically sound prediction of the total size of protistan richness in a large and varied environment, such as the Cariaco Basin: over 36 000 species, defined as almost full-length 18S rRNA gene sequence clusters sharing over 99% sequence homology. This richness is a small fraction of the grand total of known protists (over 100 000–500 000 species), suggesting a degree of protistan endemism.     

Multi-target-directed triazole derivatives as promising agents for the treatment of Alzheimer’s disease

A novel series of triazole-based compounds have been designed, synthesised and evaluated as multi-target-directed ligands (MTDLs) against Alzheimer disease (AD). The triazole-based compounds have been designed to target four major AD hallmarks that include Aβ aggregation, metal-induced Aβ aggregation, metal dys-homeostasis and oxidative stress. Among the synthesised compounds, 6n having o-CF₃ group on the phenyl ring displayed most potent inhibitory activity (96.89% inhibition, IC₅₀ = 8.065 ± 0.129 μM) against Aβ₄₂ aggregation, compared to the reference compound curcumin (95.14% inhibition, IC₅₀ = 6.385 ± 0.009 μM). Compound 6n disassembled preformed Aβ₄₂ aggregates as effectively as curcumin. Furthermore, 6n displayed metal chelating ability and significantly inhibited Cu²⁺-induced Aβ₄₂ aggregation and disassembled preformed Cu²⁺-induced Aβ₄₂ aggregates. 6n successfully controlled the generation of the reactive oxygen species (ROS) by preventing the copper redox cycle. In addition, 6n did not display cytotoxicity and was able to inhibit toxicity induced by Aβ₄₂ aggregates in SH-SY5Y cells. The preferred binding regions and key interactions of 6n with Aβ₄₂ monomer and Aβ₄₂ protofibril structure was evaluated with molecular docking. Compound 6n binds preferably to the C-terminal region of Aβ₄₂ that play a critical role in Aβ₄₂ aggregation. The results of the present study highlight a novel triazole-based compound, 6n, as a promising MTDL against AD.     

Faunal changes and geographic crypticism indicate the occurrence of a biogeographic transition zone along the southern East Pacific Rise

Aim Deep‐sea hydrothermal vents have now been reported along all active mid‐ocean ridges and back‐arc basins, but the boundaries of biogeographic entities remain questionable owing to methodological issues. Here we examine biogeographic patterns of the vent fauna along the East Pacific Rise (EPR) and determine the relative roles of regional and local factors on the distribution of biodiversity associated with mussel beds along a poorly explored zone, the southern EPR (SEPR). Location East Pacific Rise. Methods A species list of macrobenthic invertebrates along the EPR was compiled from the literature and supplemented with data recovered during the French research cruise BIOSPEEDO carried out in 2004 along the SEPR. Biogeographic patterns were assessed by combining the identification of morphological species with a molecular barcoding approach. A multivariate regression tree (MRT) analysis was performed to identify any geographic breaks, and an empirical distribution of species richness was compared with predictions provided by a mid‐domain effect model. Macrofaunal community structure associated with mussel beds along the SEPR was analysed in relation to environmental factors using cluster and canonical redundancy analyses. Results Sequencing of the cytochrome c oxidase subunit I gene revealed the occurrence of several cryptic species complexes along the EPR, with the equator separating the southern and northern clades. Furthermore, during the BIOSPEEDO cruise at least 10 still unnamed species were collected between 7°25′ S and 21°33′ S. The shift in community structure identified by MRT analysis was located south of 17°34′ S or south of 13°59′ S, depending on the data used, suggesting that the southern part of the SEPR (17°25′–21°33′ S) constitutes a biogeographic transition zone in the vent fauna along the EPR. At a regional scale, latitude combined with the type of venting was significantly correlated with the community structure associated with mussel beds. Main conclusions Together, the molecular data, in situ observations, and the distribution of species suggest that the high diversity of vent fauna species presently observed between 17°25′ S and 21°33′ S is probably a result of the overlap of several distinct biogeographic provinces. We argue that this area thus constitutes a biogeographic vent fauna transition zone along the EPR.     

Modelling biome shifts and tree cover change for 2050 in West Africa

Aim Africa is expected to face severe changes in climatic conditions. Our objectives are: (1) to model trends and the extent of future biome shifts that may occur by 2050, (2) to model a trend in tree cover change, while accounting for human impact, and (3) to evaluate uncertainty in future climate projections. Location West Africa. Methods We modelled the potential future spatial distribution of desert, grassland, savanna, deciduous and evergreen forest in West Africa using six bioclimatic models. Future tree cover change was analysed with generalized additive models (GAMs). We used climate data from 17 general circulation models (GCMs) and included human population density and fire intensity to model tree cover. Consensus projections were derived via weighted averages to: (1) reduce inter‐model variability, and (2) describe trends extracted from different GCM projections. Results The strongest predicted effect of climate change was on desert and grasslands, where the bioclimatic envelope of grassland is projected to expand into the desert by an area of 2 million km². While savannas are predicted to contract in the south (by 54 ± 22 × 10⁴ km²), deciduous and evergreen forest biomes are expected to expand (64 ± 13 × 10⁴ km² and 77 ± 26 × 10⁴ km²). However, uncertainty due to different GCMs was particularly high for the grassland and the evergreen biome shift. Increasing tree cover (1–10%) was projected for large parts of Benin, Burkina Faso, Côte d’Ivoire, Ghana and Togo, but a decrease was projected for coastal areas (1–20%). Furthermore, human impact negatively affected tree cover and partly changed the direction of the projected change from increase to decrease. Main conclusions Considering climate change alone, the model results of potential vegetation (biomes) show a ‘greening’ trend by 2050. However, the modelled effects of human impact suggest future forest degradation. Thus, it is essential to consider both climate change and human impact in order to generate realistic future tree cover projections.     

Character displacement in the fighting colours of Hetaerina damselflies

Aggression between species is a seldom-considered but potentially widespread mechanism of character displacement in secondary sexual characters. Based on previous research showing that similarity in wing coloration directly influences interspecific territorial aggression in Hetaerina damselflies, we predicted that wing coloration would show a pattern of character displacement (divergence in sympatry). A geographical survey of four Hetaerina damselfly species in Mexico and Texas showed evidence for character displacement in both species pairs that regularly occurs sympatrically. Hetaerina titia, a species that typically has large black wing spots and small red wing spots, shifted to having even larger black spots and smaller red wing spots at sites where a congener with large red wing spots is numerically dominant (Hetaerina americana or Hetaerina occisa). Hetaerina americana showed the reverse pattern, shifting towards larger red wing spots where H. titia is numerically dominant. This pattern is consistent with the process of agonistic character displacement, but the ontogenetic basis of the shift remains to be demonstrated.     

High temperature and oxygen supplementation can mitigate the effects of hypoxia on developmental stability of bilateral traits during incubation of broiler breeder eggs

Hypoxia strongly affects embryonic development during the pre-hatch period. This study was conducted to investigate the effects of oxygen supplementation (O) and a 38.5°C high temperature (HT) at high altitude (HA, 1720 m) on morphological traits during a pre-hatch period and on relative fluctuating asymmetry (relative FA) and allometric growth during an early post-hatch period in broilers. A total of 720 eggs were obtained from a 45-week-old Ross 308 broiler breeder flock raised at sea level (2 m). The eggs were divided into six incubation condition (IC) groups and were incubated at HA. O groups were exposed to 23.5% O₂ for 1 h daily from either days 0 to 11 (O_0–11), days 12 to 21 (O_12–21) or days 18 to 21 (O_18–21) of incubation. HT groups were exposed to 38.5°C daily from either days 12 to 21 (HT_12–21) or days 18 to 21 (HT_18–21) of incubation. A control was maintained at 37.8°C and 21% O₂. The hatched chicks were raised for 6 days at HA. Embryo/chick and beak lengths and head diameter were measured during pre- and post-hatch periods. The face, middle toe and shank lengths were measured for each chick. The relative asymmetry (RA), mean RA (MRA) and allometric growth of the lengths were computed and the existence of FA was demonstrated. The IC significantly affected the embryo length, with embryos of the O_0–11 group shorter than embryos of the other O groups. Chicks were longer in the O and HT groups than those in the control, except for the O_0–11. We found significant interactions between the IC and each development period for beak length. During the post-hatch period, the head diameter of the O_0-11 was significantly smaller than that of the other groups, but not in O_12–21. The interactions among IC, age and sex were significant for the RA of the face and middle toe lengths and for MRA. All the examined bilateral traits were evaluated as allometric growth. The FA for bilateral traits was determined in both sexes. The right (R) – left (L) and IR-Ll were the lowest in females for face length and in males for shank length from the O_18–21 and in males for middle toe length from the O_0–11 and HT_18–21 groups. Therefore, the effects of factors such as HT and O₂ could mitigate the adverse effects of HA-induced hypoxia on optimal developmental stability of bilateral traits of broiler.