Vegetation dynamics in a Quercus‐Juniperus savanna: An isotopic assessment

Abstract. Woody plants are increasing in many grassland and savanna ecosystems around the world. As a case in point, the Edwards Plateau of Texas, USA, is a vast region (93 000 km²) in which rapid woody encroachment appears to be occurring. The native vegetation (prior to the Anglo‐European settlement 150–200 yr ago) and the biogeochemical consequences of woody encroachment in this region, however, are poorly understood. To assess these matters we measured plant and soil δ¹³C, soil organic C and soil N content from grasslands and two important woody patch types (mature Quercus virginiana clusters and Juniperus ashei woodlands) in this region. Soil δ¹³C values showed that relative productivity of C₃ species has increased in grassland and both woody habitats in recent times. δ¹³C of SOC in grasslands and Q. virginiana clusters increased with depth from the litter layer to 30 cm (grasslands =?21 to ?13‰Q. virginiana clusters =?27 to ?17‰) and were significantly different between habitats at all depths, indicating that Q. virginiana has been a long‐term component of the landscape. In J. ashei woodlands, soil δ¹³C values (at 20–30 cm depth) near the woodland edge (‐13‰) converged with those of an adjacent grassland (‐13‰) while those from the woodland interior (‐15‰) remained distinct, indicating that the woodland has been present for many years but has recently expanded. Concentrations and densities of SOC and total N were generally greater in woody patches than in grasslands. However, differences in the amount of SOC and N stored beneath the two woody patch types indicates that C and N sequestration potentials are species dependent.     

Seed germination of Agave species as influenced by substrate water potential

Background

Plants of Agave spp. perform Crassulacean acid metabolism (CAM) and are highly drought-tolerant, but little is known concerning seed germination under low water availability. The aim of this study was to assess the effect of substrate water potential (Ψ_W) on seed germination and contrast hydrotime parameters of seven valuable and commercially-important Agave species from different geographical distributions and climatic regions of Mexico. Our hypothesis was that seed germination of Agave species is not affected by low water availability independently of seed biomass and the climate of their distribution area.

Results

Seed germination (at 25°C and in the dark) between 85 and 100% for all species occurred within 80–180 h at -0.03 MPa and 250–430 h at -1.0 MPa. Seed germination at -1.5 MPa declined to less than 50% (p < 0.05) for A. asperrima and A. cupreata but did not change significantly for A. americana var. marginata, A. lechuguilla and A. striata, although they showed the lowest mean base water potential (-2.01 to -2.64 MPa). Seed germination of 40% Agave species, from arid and semi-arid climates in this study, was not affected by the lower Ψ_W.

Conclusion

Germination of seeds of Agave species is moderately affected by low water availability, is partially dependent of their ecological distribution, and is independent of seed mass.     

Biotechnological challenges of bioartificial kidney engineering

With the world-wide increase of patients with renal failure, the development of functional renal replacement therapies have gained significant interest and novel technologies are rapidly evolving. Currently used renal replacement therapies insufficiently remove accumulating waste products, resulting in the uremic syndrome. A more preferred treatment option is kidney transplantation, but the shortage of donor organs and the increasing number of patients waiting for a transplant warrant the development of novel technologies. The bioartificial kidney (BAK) is such promising biotechnological approach to replace essential renal functions together with the active secretion of waste products. The development of the BAK requires a multidisciplinary approach and evolves at the intersection of regenerative medicine and renal replacement therapy. Here we provide a concise review embracing a compact historical overview of bioartificial kidney development and highlighting the current state-of-the-art, including implementation of living-membranes and the relevance of extracellular matrices. We focus further on the choice of relevant renal epithelial cell lines versus the use of stem cells and co-cultures that need to be implemented in a suitable device. Moreover, the future of the BAK in regenerative nephrology is discussed.     

Phylogenetic reconstruction of endophytic fungal isolates using internal transcribed spacer 2 (ITS2) region

Endophytic fungi are inhabitants of plants, living most part of their lifecycle asymptomatically which mainly confer protection and ecological advantages to the host plant. In this present study, 48 endophytic fungi were isolated from the leaves of three medicinal plants and characterized based on ITS2 sequence – secondary structure analysis. ITS2 secondary structures were elucidated with minimum free energy method (MFOLD version 3.1) and consensus structure of each genus was generated by 4SALE. ProfDistS was used to generate ITS2 sequence structure based phylogenetic tree respectively. Our elucidated isolates were belonging to Ascomycetes family, representing 5 orders and 6 genera. Colletotrichum/Glomerella spp., Diaporthae/Phomopsis spp., and Alternaria spp., were predominantly observed while Cochliobolus sp., Cladosporium sp., and Emericella sp., were represented by singletons. The constructed phylogenetic tree has well resolved monophyletic groups with >50% bootstrap value support. Secondary structures based fungal systematics improves not only the stability; it also increases the precision of phylogenetic inference. Above ITS2 based phylogenetic analysis was performed for our 48 isolates along with sequences of known ex-types taken from GenBank which confirms the efficiency of the proposed method. Further, we propose it as superlative marker for reconstructing phylogenetic relationships at different taxonomic levels due to their lesser length.     

A new agenda for blue agave landraces: food,energy and tequila

Agave tequilana Weber (Rigidae, Agavaceae), blue agave, is a native Mexican plant that has been associated with tequila since the 17th century. The tequila industry has matured over time and now has a geographical indication (Denominación de Origen; DOT). The tequila industry has grown substantially in the last 15 years (19.82% annual increase between 1995 and 2008), resulting in an increase in agave production and associated residue (leaves) and bagasse that can be used for second‐generation biofuels. At a time when the biofuel industry is undergoing unprecedented changes, with diversified demand and predictions of increased competitiveness, this paper presents a review of agave landraces that have been affected by tequila production but may be beneficial for a biofuel industry. Conventional botanical studies have revealed domestication syndromes in races related to blue agave (‘azul listado’, ‘sigüín’ and ‘pata de mula’) specifically for production of fructans in the plant core as would be expected in mezcal agaves (including those used for tequila). Some others, such as the ‘moraleño’ and ‘bermejo’ cultivars (Sisalanae) show domestication syndrome only in the fibers, while others, such as ‘chato,’A. americana L. subtilis (Americanae) show domestication syndrome in fructans and fibers and ‘zopilote,’A. rhodacantha (Rigidae) a relatively low domestication syndrome. No specimens of the cultivars named ‘mano larga’, ‘mano anchaque’ and ‘cucharo’ were found in the Tequila Region of Origin (Western Mexico). The genetic resources from landraces ignored by the tequila industry may be valuable for both ethanol production and conservation.     

Kir5.1 underlies long-lived subconductance levels in heteromeric Kir4.1/Kir5.1 channels from Xenopus tropicalis

The inwardly-rectifying potassium channel subunit Kir5.1 selectively co-assembles with members of the Kir4.0 subfamily to form novel pH-sensitive heteromeric channels with unique single channel properties. In this study, we have cloned orthologs of Kir4.1 and Kir5.1 from the genome of the amphibian, Xenopus tropicalis (Xt). Heteromeric XtKir4.1/XtKir5.1 channels exhibit similar macroscopic current properties to rat Kir4.1/Kir5.1 with a faster time-dependent rate of activation. However, single channel analysis of heteromeric XtKir4.1/XtKir5.1 channels reveals that they have markedly different long-lived, multi-level subconductance states. Furthermore, we demonstrate that the XtKir5.1 subunit is responsible for these prominent subconductance levels. These results are consistent with a model in which the slow transitions between sublevel states represent the movement of individual subunits. These novel channels now provide an excellent model system to determine the structural basis of subconductance levels and contribution of heteromeric pore architecture to this process.     

Distribution of Cell Adhesion Molecules (CAM) along the Branching Neurite Surface: Model-Inherited Effects of the Branch Diameters and Mode of CAM Transport

In many cases, an increase in the surface density of cell adhesion molecules (CAM) in the distal parts of a growing neurite is favorable for the neurite elongation. This increase is attained by exocytotic insertion of CAM-containing vesicles into the growth cones with subsequent redistribution of CAM along the cell surface due to lateral diffusion and endocytosis. Using a mathematical model describing these processes, we quantitatively describe conditions providing two qualitatively different profiles in a branching neurite: (i) the CAM surface density increases along both daughter branches, which would be in favor of further outgrowth of both branches, i.e., successful branching, or (ii) the CAM surface density increases along one daughter branch and decreases along another branch, which could lead to the retraction of the latter. The geometric factors and mechanisms underlying the intracellular CAM transport to the daughter growth cones were proved to determine the profile of CAM surface density. A similarity in the diameters of daughter branches, their short lengths, a high value of the lateral transfer constant, and partitioning of CAM transport at the branching point proportionally to the surface areas of daughter branches are in favor of an increase in the CAM surface density along both daughter branches. Asymmetric branching can lead to a decrease in the CAM surface density along the thinner or thicker daughter branch, if CAM trafficking was equally partitioned or was proportional to the branch cross-sectional areas, respectively. The proposed model helps to understand possible relationships between the intracellular CAM trafficking, CAM surface distribution, and geometry of branching of the neurites.     

Restoration of p53/miR-34a regulatory axis decreases survival advantage and ensures Bax-dependent apoptosis of non-small cell lung carcinoma cells

Tumor-suppressive miR-34a, a direct target of p53, has been shown to target several molecules of cell survival pathways. Here, we show that capsaicin-induced oxidative DNA damage culminates in p53 activation to up-regulate expression of miR-34a in non-small cell lung carcinoma (NSCLC) cells. Functional analyses further indicate that restoration of miR-34a inhibits B cell lymphoma-2 (Bcl-2) protein expression to withdraw the survival advantage of these resistant NSCLC cells. In such a proapoptotic cellular milieu, where drug resistance proteins are also down-regulated, p53-transactivated Bcl-2 associated X protein (Bax) induces apoptosis via the mitochondrial death cascade. Our results suggest that p53/miR-34a regulatory axis might be critical in sensitizing drug-resistant NSCLC cells.     

Recent developments in mesophyll conductance in C3, C4, and crassulacean acid metabolism plants

The conductance of carbon dioxide (CO₂) from the substomatal cavities to the initial sites of CO₂ fixation (g_m) can significantly reduce the availability of CO₂ for photosynthesis. There have been many recent reviews on: (i) the importance of g_m for accurately modelling net rates of CO₂ assimilation, (ii) on how leaf biochemical and anatomical factors influence g_m, (iii) the technical limitation of estimating g_m, which cannot be directly measured, and (iv) how g_m responds to long‐ and short‐term changes in growth and measurement environmental conditions. Therefore, this review will highlight these previous publications but will attempt not to repeat what has already been published. We will instead initially focus on the recent developments on the two‐resistance model of g_m that describe the potential of photorespiratory and respiratory CO₂ released within the mitochondria to diffuse directly into both the chloroplast and the cytosol. Subsequently, we summarize recent developments in the three‐dimensional (3‐D) reaction‐diffusion models and 3‐D image analysis that are providing new insights into how the complex structure and organization of the leaf influences g_m. Finally, because most of the reviews and literature on g_m have traditionally focused on C₃ plants we review in the final sections some of the recent developments, current understanding and measurement techniques of g_m in C₄ and crassulacean acid metabolism (CAM) plants. These plants have both specialized leaf anatomy and either a spatially or temporally separated CO₂ concentrating mechanisms (C₄ and CAM, respectively) that influence how we interpret and estimate g_m compared with a C₃ plants.