Diversity of Xiphinema americanum-group Species and Hierarchical Cluster Analysis of Morphometrics

Of the 39 species composing the Xiphinema americanum group, 14 were described originally from North America and two others have been reported from this region. Many species are very similar morphologically and can be distinguished only by a difficult comparison of various combinations of some morphometric characters. Study of morphometrics of 49 populations, including the type populations of the 39 species attributed to this group, by principal component analysis and hierarchical cluster analysis placed the populations into five subgroups, proposed here as the X. brevicolle subgroup (seven species), the X. americanum subgroup (17 species), the X. taylori subgroup (two species), the X. pachtaicum subgroup (eight species), and the X. lambertii subgroup (five species).     

Cryptophytes: An emerging algal group in the rapidly changing Antarctic Peninsula marine environments

The western Antarctic Peninsula (WAP) is a climatically sensitive region where foundational changes at the basis of the food web have been recorded; cryptophytes are gradually outgrowing diatoms together with a decreased size spectrum of the phytoplankton community. Based on a 11-year (2008–2018) in-situ dataset, we demonstrate a strong coupling between biomass accumulation of cryptophytes, summer upper ocean stability, and the mixed layer depth. Our results shed light on the environmental conditions favoring the cryptophyte success in coastal regions of the WAP, especially during situations of shallower mixed layers associated with lower diatom biomass, which evidences a clear competition or niche segregation between diatoms and cryptophytes. We also unravel the cryptophyte photo-physiological niche by exploring its capacity to thrive under high light stress normally found in confined stratified upper layers. Such conditions are becoming more frequent in the Antarctic coastal waters and will likely have significant future implications at various levels of the marine food web. The competitive advantage of cryptophytes in environments with significant light level fluctuations was supported by laboratory experiments that revealed a high flexibility of cryptophytes to grow in different light conditions driven by a fast photo-regulating response. All tested physiological parameters support the hypothesis that cryptophytes are highly flexible regarding their growing light conditions and extremely efficient in rapidly photo-regulating changes to environmental light levels. This plasticity would give them a competitive advantage in exploiting an ecological niche where light levels fluctuate quickly. These findings provide new insights on niche separation between diatoms and cryptophytes, which is vital for a thorough understanding of the WAP marine ecosystem.     

Evidence for nuclear internalization of exogenous DNA into mammalian sperm cells

Mature sperm cells have the spontaneous capacity to take up exogenous DNA. Such DNA specifically interacts with the subacrosomal segment of the sperm head corresponding to the nuclear area. Part of the sperm-bound foreign DNA is further internalized into nuclei. Using end-labelled plasmid DNA we have found that 15–22% of the total sperm bound DNA is associated with nuclei as determined on isolated nuclei. On the basis of autoradiographic analysis, nuclear permeability to exogenous DNA seems to be a wide phenomenon involving the majority of the sperm nuclei. In fact, the foreign DNA, incubated with sperm cells for different lengths of time, is found in 45% (10 min) to 65% (2 hr) of the sperm nuclei. Ultrastructural autoradiography on thin sections of mammalian spermatozoa, preincubated with end-labelled plasmid DNA, shows that the exogenous DNA is internalized into the nucleus. This conclusion is further supported by ultrastructural autoradiographic analysis on thin sections of nuclei isolated from spermatozoa preincubated with end-labelled DNA. © 1993 Wiley-Liss, Inc.     

Thermal biology and locomotor performance of the Andean lizard Liolaemus fitzgeraldi (Liolaemidae) in Argentina

Ectotherms thermoregulate to maintain their body temperature within the optimal range needed for performing vital functions. The effect of climate change on lizards has been studied as regards the sensitivity of locomotor performance to environmental temperatures. We studied thermoregulatory efficiency and locomotor performance for Liolaemus fitzgeraldi in the Central Andes of Argentina. We determined body temperature, micro-environmental temperatures and operative temperatures in the field. In the laboratory, we measured preferred temperatures and calculated the index of thermoregulatory efficiency. We estimated the thermal sensitivity of locomotion by measuring sprint speed (initial velocity and long sprint) and endurance at five different body temperatures. Body temperature was not associated with either micro-environmental temperature, nor did it show differences with preferred temperatures. Thermoregulatory efficiency was moderate (0.61). Initial velocity and long sprint trials showed differences at different temperatures; however, endurance did not. Moreover, the optimal temperatures for the performance trials showed no significant differences among themselves. We conclude that Liolaemus fitzgeraldi has thermal sensitivity in locomotor performance with respect to body temperature and that it is an eurythermic lizard that experiences a large variation in body temperature and that has thermal flexibility in the cold.     

Inflorescence-specific genes from Arabidopsis thaliana encoding glycine-rich proteins

Genomic and cDNA clones for three inflorescence-specific genes from Arabidopsis thaliana were isolated and characterized. The genes are tandemly organized in the genome on a 10 kb fragment. The expression of these genes is coordinately regulated in a developmental and organ-specific pattern. They are expressed predominantly in anthers at the later stage of flower development. The primary structure of the encoded gene products exhibits comparable features consisting of a hydrophobic domain at the N-terminal region followed by repeated glycine-rich motifs. Little homology is observed either between the glycine-rich domain of the three genes or with previously described glycine-rich proteins from other plant species.     

Copper Toxicity in Maize: The Severity of the Stress is Reduced Depending on the Applied Fe-Chelating Agent

Journal of Plant Growth Regulation - The wide use of copper (Cu)-based fungicide has caused a stepwise accumulation of Cu in the environment increasing the occurrence of phytotoxicity in crops. To...     

Non-histone protein methylation in Trypanosoma cruzi epimastigotes

Post-translational methylation of proteins, which occurs in arginines and lysines, modulates several biological processes at different levels of cell signaling. Recently, methylation has been demonstrated in the regulation beyond histones, for example, in the dynamics of protein-protein and protein-nucleic acid interactions. However, the presence and role of non-histone methylation in Trypanosoma cruzi, the etiologic agent of Chagas disease, has not yet been elucidated. Here, we applied mass spectrometry-based-proteomics (LC-MS/MS) to profile the methylproteome of T. cruzi epimastigotes, describing a total of 1252 methyl sites in 824 proteins. Functional enrichment and protein-protein interaction analysis show that protein methylation impacts important biological processes of the parasite, such as translation, RNA and DNA binding, amino acid, and carbohydrate metabolism. In addition, 171 of the methylated proteins were previously reported to bear phosphorylation sites in T. cruzi, including flagellar proteins and RNA binding proteins, indicating that there may be an interplay between these different modifications in non-histone proteins. Our results show that a broad spectrum of functions is affected by methylation in T. cruzi, indicating its potential to impact important processes in the biology of the parasite and other trypanosomes.     

Effects of Removal of Successful Males in a Fallow Deer Lek

Removal of 5 of the 8 most successful males in a fallow deer lek between breeding seasons led to an increase in fighting rate of males and a decrease in mating rate of both sexes. The increase in fighting was likely due to disruption of the social hierarchy. The lower mating rate of females was not due to disruption of copulations by territorial males, nor did it appear to result from disturbance from fights. We suggest that difficulties in mate choice related to an unstable male hierarchy resulted in females either increasing their length of stay in the lek, visiting the lek more than once before mating, or leaving the lek without mating.     

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM treeClusia hilariana

Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO₂ fixation rates of 28 mol m^-2 s^-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (q_N) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO₂ fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (q_A) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of q_A throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (F_v/F_m) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in F_v/F_m, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition.     

Hydrogen Peroxide Induces a Long-Lasting Inhibition of the Ca2+-Dependent Glutamate Release in Cerebrocortical Synaptosomes Without Interfering with Cytosolic Ca2+

Abstract: We studied the action of H₂O₂ on the exocytosis of glutamate by cerebrocortical synaptosomes. The treatment of synaptosomes with H₂O₂ (50–150 µ M ) for a few minutes results in a long-lasting depression of the Ca²⁺-dependent exocytosis of glutamate, induced by KCl or by the K⁺-channel inhibitor 4-aminopyridine. The energy state of synaptosomes, as judged by the level of phosphocreatine and the ATP/ADP ratio, was not affected by H₂O₂, although a transient decrease was observed after the treatment. H₂O₂ did not promote peroxidation, as judged by the formation of malondialdehyde. In indo-1-loaded synaptosomes, the treatment with H₂O₂ did not modify significantly the KCl-induced increase of [Ca²⁺]_i. H₂O₂ inhibited exocytosis also when the latter was induced by increasing [Ca²⁺]_i with the Ca²⁺ ionophore ionomycin. The effects of H₂O₂ were unchanged in the presence of superoxide dismutase and the presence of the Fe³⁺ chelator deferoxamine. These results appear to indicate that H₂O₂, apparently without damaging the synaptosomes, induces a long-lasting inhibition of the exocytosis of glutamate by acting directly on the exocytotic process.