Ultrastructural and Biogeochemical Features of Microbiotic Soil Crusts and their Implications in a Semi-Arid Habitat

This investigation was designed to explore the relationships between lichen symbionts (phycobiont and mycobiont) and the substrate on which they grow by examining the chemical and ultrastructural features of the lichen-soil interface. These lichens form an integral part of microbiotic soil crusts. Fragments of three different lichen biotypes growing over gypsum crystals and marls were fixed and embedded in resin. The lichen-substratum interface was then examined by scanning electron microscopy with backscattered electron imaging. In situ observation, microanalytical (EDS), and FT-Raman plus infrared spectroscopy of the lichen-substratum interface indicated that different ultrastructural features of the mycobiont were related to biogeochemical processes and Ca 2+ distribution in the soil crust. Phycobionts were observed to make direct contact with the substratum and to be surrounded by a nondifferentiated thallus structure. These observations suggest that they can grow outside the thallus in the early stages of lichen development in the semi-arid conditions of their habitat. The particular ultrastructural features of the lichen thallus and of the lichen-substratum interface appear to have marked effects on runoff phenomena and ponding generation of the surface.     

Subspecies delineation amid phenotypic,geographic and genetic discordance in a songbird

Understanding the processes that drive divergence within and among species is a long‐standing goal in evolutionary biology. Traditional approaches to assessing differentiation rely on phenotypes to identify intra‐ and interspecific variation, but many species express subtle morphological gradients in which boundaries among forms are unclear. This intraspecific variation may be driven by differential adaptation to local conditions and may thereby reflect the evolutionary potential within a species. Here, we combine genetic and morphological data to evaluate intraspecific variation within the Nelson's (Ammodramus nelsoni) and salt marsh (Ammodramus caudacutus) sparrow complex, a group with populations that span considerable geographic distributions and a habitat gradient. We evaluated genetic structure among and within five putative subspecies of A. nelsoni and A. caudacutus using a reduced‐representation sequencing approach to generate a panel of 1929 SNPs among 69 individuals. Although we detected morphological differences among some groups, individuals sorted along a continuous phenotypic gradient. In contrast, the genetic data identified three distinct clusters corresponding to populations that inhabit coastal salt marsh, interior freshwater marsh and coastal brackish–water marsh habitats. These patterns support the current species‐level recognition but do not match the subspecies‐level taxonomy within each species—a finding which may have important conservation implications. We identified loci exhibiting patterns of elevated divergence among and within these species, indicating a role for local selective pressures in driving patterns of differentiation across the complex. We conclude that this evidence for adaptive variation among subspecies warrants the consideration of evolutionary potential and genetic novelty when identifying conservation units for this group.     

Causal role of oxidative stress in liver preconditioning by thyroid hormone in rats

Hepatic ischemia-reperfusion (IR) injury, a major clinical drawback during surgery, is abolished by L-3,3',5-triiodothyronine (T(3)) administration. Considering that the triggering mechanisms are unknown, the aim of this study is to assess the role of oxidative stress in T(3) preconditioning using N-acetylcysteine (NAC) before T(3) administration. Male Sprague-Dawley rats given a single dose of 0.1 mg of T(3)/kg were subjected to 1 h ischemia followed by 20 h reperfusion, in groups of animals pretreated with 0.5 g of NAC/kg 0.5 h before T(3) or with the respective control vehicles. At the end of the reperfusion period, blood and liver samples were taken for analysis of serum aspartate aminotransferase (AST) and hepatic histology, glutathione (GSH) and protein carbonyl contents, and nuclear factor-kappaB (NF-kappaB) and activating protein 1 (AP-1) DNA binding. The IR protocol used led to a 4.5-fold increase in serum AST levels and drastic changes in liver histology, with significant GSH depletion and enhancement of protein carbonyl levels and of the protein carbonyl/GSH content ratio, whereas NF-kappaB and AP-1 DNA binding was decreased and enhanced, respectively. In a time window of 48 h, T(3) exerted protection against hepatic IR injury, with 88% reduction in the protein carbonyl/GSH ratio and normalization of NF-kappaB and AP-1 DNA binding, changes that were suppressed by NAC administration before T(3). Data presented suggest that a transient increase in the oxidative stress status of the liver is an important trigger for T(3) preconditioning, evidenced in a warm IR injury model through antioxidant intervention.     

A Secreted Effector Protein of Ustilago maydis Guides Maize Leaf Cells to Form Tumors

The biotrophic smut fungus Ustilago maydis infects all aerial organs of maize (Zea mays) and induces tumors in the plant tissues. U. maydis deploys many effector proteins to manipulate its host. Previously, deletion analysis demonstrated that several effectors have important functions in inducing tumor expansion specifically in maize leaves. Here, we present the functional characterization of the effector See1 (Seedling efficient effector1). See1 is required for the reactivation of plant DNA synthesis, which is crucial for tumor progression in leaf cells. By contrast, See1 does not affect tumor formation in immature tassel floral tissues, where maize cell proliferation occurs independent of fungal infection. See1 interacts with a maize homolog of SGT1 (Suppressor of G2 allele of skp1), a factor acting in cell cycle progression in yeast (Saccharomyces cerevisiae) and an important component of plant and human innate immunity. See1 interferes with the MAPK-triggered phosphorylation of maize SGT1 at a monocot-specific phosphorylation site. We propose that See1 interferes with SGT1 activity, resulting in both modulation of immune responses and reactivation of DNA synthesis in leaf cells. This identifies See1 as a fungal effector that directly and specifically contributes to the formation of leaf tumors in maize.     

Description of two new species of Glypthelmins Stafford, 1905 (Digenea: Macroderoididae) in Rana spp. from Mexico, based on morphology and mtDNA and rDNA sequences

Glypthelmins Stafford, 1905 includes 29 putative species commonly found in the intestine and liver of anurans from all over the world but mainly in the Americas. Partial sequences of the cytochrome c oxidase subunit 1 ( cox 1), ribosomal internal transcribed spacer region 2 (ITS2) and the large subunit 28S rDNA gene were obtained and analysed using pairwise distance matrices and parsimony methods in order to characterise the interrelationships between 14 isolates of four nominal species of Glypthelmins recognised on morphological grounds. The highest intra-specific sequence divergence occurred in the cox 1 (18.53%) sequence, followed by that of the ITS2 (5.44%) and 28S (4.63%). Genetic variability was detected between the three isolates originally identified as G. facioi Brenes et al., 1959 from two localities in Mexico and one locality in Costa Rica. Sequence divergence exhibited among these isolates ranged from 10.70 to 11.22%, from 0.48 to 0.97% and from 1.33 to 1.88% for cox 1, ITS2 and 28S, respectively. Phylogenetic analysis combining all three data-sets generated a single most parsimonious tree. The three isolates of G. facioi form a clade, with an isolate collected from frogs in Veracruz State as the sister group to an isolate from Tabasco State + G. facioi from Costa Rica. The information derived from pairwise distance of independent data-sets plus the phylogenetic information indicate that each of the two isolates from Mexico, identified a priori as G. facioi, represent separate species. A re-examination of specimens was carried out and a re-evaluation made of the morphological characters to find reliable differences that had been overlooked. As a consequence, G. brownorumae n. sp. from Tabasco and G. tuxtlasensis n. sp. from Veracruz are described based on molecular and morphological differences.     

THE FINE STRUCTURE OF THE AXON AND GROWTH CONE OF THE DORSAL ROOT NEUROBLAST OF THE RABBIT EMBRYO

The centrally directed neurite of the dorsal root neuroblast has been described from the period of its initial entrance into the neural tube until a well-defined dorsal root is formed. Large numbers of microtubules, channels of agranular reticulum, and clusters of ribosomes are found throughout the length of the early axons. The filopodia of the growth cone appear as long thin processes or as broad flanges of cytoplasm having a finely filamentous matrix material and occasionally small ovoid or elongate vesicles. At first the varicosity is a small expansion of cytoplasm, usually containing channels of agranular reticulum and a few other organelles. The widely dilated cisternae of agranular reticulum frequently found within the growth cone probably correspond to the pinocytotic vacuoles seen in neurites in tissue culture. The varicosities enlarge to form bulbous masses of cytoplasm, which may measure up to 5 µ in width and 13 µ in length. They contain channels of agranular reticulum, microtubules, neurofilaments, mitochondria, heterogeneous dense bodies, and a few clusters of ribosomes. Large ovoid mitochondria having ribonucleoprotein particles in their matrix are common. Dense membrane specializations are found at the basal surface of the neuro-epithelial cell close to the area where the early neurites first enter the neural tube.     

EVIDENCE FOR THE OCCURRENCE AND DISTRIBUTION OF INORGANIC POLYPHOSPHATES IN VERTEBRATE TISSUES

Evidence for the occurrence of polyphosphates having apparent chain-lengths ranging from less than 10 to over 5000 orthophosphate units has been found in adult brain as well as in a number of other mammalian tissues which have been examined. There appears to be three times as much polyphosphate in rat brain as there is in rat liver. Adult rat brain appears to contain at least 15 μg of phosphorus as polyphosphate per g of fresh tissue. In addition, neural polyphosphate is extremely labile to catabolic degradation after death whereas hepatic polyphosphate is relatively more stable. The nature of this inorganic polymer was elucidated through use of the technique of ³¹P nuclear magnetic resonance spectroscopy. Further structural evidence was obtained by application of the isotopic dilution technique to ³²P-labelled neural polyphosphate mixed with an abiotically prepared inorganic polyphosphate. The conditions and rates of hydrolysis of the biological polyphosphate and a non-biological polyphosphate were comparable.