Effects of environment,seedling age,and seed source on leaf resistance of three species of Chamaecyparis and Tsuga chinensis

Summary The objectives of this study were to determine how stomata of Chamaecyparis spp. react to environmental changes and to determine in what ways leaf resistance patterns may have adaptive value for these confers. Leaf resistances were measured of Chamaecyparis taiwanensis, C. formosensis and C. lawsoniana seedlings in a forest nursery, and of saplings of the first two species and Tsuga chinensis growing in natural forest and clearcuts. Light, temperature, humidity, and sometimes xylem pressure potential were measured concurrently.In the nursery, C. lawsoniana, the species from the driest climate, had the lowest resistance, daily means for well-watered yearold plants being 2–5 s cm^-1. Leaf resistances of well-watered C. formosensis and C. taiwanensis from more humid habitats were two and three times greater. Leaf resistance was more sensitive to environment in those nursery populations of C. formosensis from habitats where a dry season is more severe. There were no clear patterns of variation within the other species. Resistance of scale leaves increased with seedling size and age. Primary leaves of C. formosensis had higher average resistance than its scale leaves, and were more responsive to changes in the environment.In the field, C. taiwanensis had higher resistance than C. formosensis. Leaf resistance of Tsuga chinesis was quite similar to that of C. formosensis. Resistance decreased from winter to spring except during a severe dry spell in March.Changes in leaf resistance were most consistently correlated with humidity, which often increased during the day as humid air rose from the lowlands. Stomata opened as humidity rose even when plant xylem pressure potentials were -15 to -23 bars. Stomatal reaction of Chamaecyparis spp. varies in ways apparently adaptive to their environment.     

A whole-system reconsideration of paradigms about photoperiod and temperature control of crop yield

Summary Effects by photoperiod gene(s) and daylength on crop yield and its three major physiological components (aerial biomass, harvest index, and days to harvest maturity) are reviewed for bean (Phaseolus vulgaris L.) and peanut (Arachis hypogaea L.). In these plus many other cited crops, photoperiod sensitive gene(s) delay days to flowering and/or days to maturity in non-promotive daylength while simultaneously lowering the harvest index. Thus, for many crops, earlier maturity is associated with higher harvest index, and/or it has been shown that photoperiod gene(s) control partitioning of photosynthate toward reproductive growth versus toward competitive partitioning to continued vegetative growth. Our conclusion is that photoperiod gene control over this partitioning precedes and is causal of the photoperiodgene control over days to flowering and maturity. This implies shifts from commonly accepted paradigms about effects by photoperiod and about breeding for higher yield. These paradigm shifts suggest more efficient ways to breed for cultivar adaption to the specific growing season duration and environment of each geographical site and for higher crop yield.     

An experimental test of diversity maintenance mechanisms,by a species removal experiment in a species-rich wooded meadow

Most theories of plant species coexistence assume the presence of diversity maintenance mechanisms, i.e. mechanisms enhancing species richness in a community. We wished to determine whether such a mechanism was operating by establishing a field experiment in the species-rich wooded meadow of Laelatu, western Estonia. Ten to seventeen subordinate species were removed periodically (for 4 years) from 10 permanent plots of 1×1 m (each plot had its specific list of excluded species; 10 plots served as control). Since the removed species were all subordinate ones, very little biomass was removed, but at the same time richness was reduced by 25–33%. If some diversity maintenance mechanism was operating, we would expect that immigration of other subordinate species would restore the original species richness. It was not possible to reject the null hypothesis of an identical immigration rate of new species into manipulated and control plots. The rate of small-scale species turnover was not affected by the removal of subordinate species. Interrelations of five richness characteristics were studied, by comparing empirical correlations among them, with those expected from a null model of random migration of species. The immigration rate of new species appeared to be related to the number of constant species, and immigration/extinction balance related to initial richness, more strongly than predicted by the null model. In the manipulated series these relationships matched the expectation from the null model. While the results generally support the so-called species pool hypothesis (and the carousel model), it seems that species small-scale turnover depends on the richness pattern in the studied grassland. In the case of plots with artificially reduced richness no departures can be detected from the random migration hypothesis.     

Novel N-substituted benzimidazole CXCR4 antagonists as potential anti-HIV agents

The lead optimization of a series of N-substituted benzimidazole CXCR4 antagonists is described. Side chain modifications and stereochemical optimization led to substantial improvements in potency and protein shift to afford compounds with low nanomolar anti-HIV activity.     

What determines the relationship between plant diversity and habitat productivity?

The relationship between biodiversity and habitat productivity has been a fundamental topic in ecology. Although the relationship between these parameters may exhibit different shapes, the unimodal shape has been frequently encountered. The decrease in diversity at high productivity has usually been attributed to competitive exclusion. We suggest that evolutionary history and dispersal limitation may be even more important in shaping the diversity–productivity relationship. On a global scale, unimodal diversity–productivity relationships dominate in temperate regions, whereas positive relationships are more common in the tropics. This difference can be accounted for by contrasting evolutionary history. Temperate regions have smaller species pools for productive habitats since these habitats have been scarce historically for speciation, while the opposite is true for the tropics. In addition, dispersal within a region may limit diversity either due to the lack of dispersal syndromes at low productivity or the low number of diaspores at high productivity. Thereafter, biotic interactions (competition and facilitation) can shape the relationship. All these processes can act independently or concurrently. We recommend that the common approach to examining empirical diversity–environmental relationships should start with the role of large‐scale processes such as evolutionary history and dispersal limitation, followed by influences associated with ecological interactions.     

High diversity of arbuscular mycorrhizal fungi in a boreal herb-rich coniferous forest

* Here, the diversity of arbuscular mycorrhizal (AM) fungi was determined in a boreal herb-rich coniferous forest in relation to environmental variables. * Root samples of five plant species (Fragaria vesca, Galeobdolon luteum, Hepatica nobilis, Oxalis acetosella and Trifolium pratense) were analysed from stands differing in age and forest management intensity. * Thirty-four Glomeromycota taxa (small-subunit ribosomal RNA gene (SSU rDNA) sequence groups) were detected from 90 root samples (911 clones), including eight new taxa. Sequence groups related to Glomus intraradices were most common (MO-G3 and MO-G13). Samples of H. nobilis were colonized by more AM fungal taxa (3.68 +/- 0.31) than those of O. acetosella (2.69 +/- 0.34), but did not differ significantly in this respect from those of F. vesca (3.15 +/- 0.38). Effects of forest management, host plant species (except above) or season on the number or composition of fungal taxa in root samples were not detected, and neither were they explained by environmental variables (vegetation, soil and light conditions). * This is the most taxon-rich habitat described to date in terms of root-colonizing Glomeromycota. The data demonstrate the importance of temperate coniferous forests as habitats for AM fungi and plants. Lack of obvious fungal community patterns suggests more complex effects of biotic and abiotic factors, and possibly no adverse effect of common forest management practices on AM fungal diversity.     

Sarcoplasmic Ca2+ release is prolonged in nonfailing myocardium of diabetic patients

Background Asymptomatic diabetic patients have a high incidence of clinically unrecognized left ventricular dysfunction with an abnormal cardiac response to exercise. We, therefore, examined subclinical defects in the contraction–relaxation cycle and intracellular Ca²⁺ regulation in myocardium of asymptomatic type 2 diabetic patients. Methods Alterations in the dynamics of the intracellular Ca²⁺ transient and contractility were recorded in right atrial myocardium of type 2 diabetic patients and non-diabetic control tissue loaded with fura-2. In order to gain an insight into mechanisms underlying the altered Ca²⁺ handling in diabetic myocardium levels of mRNA, protein expression and phosphorylation of key proteins in sarcoplasmic Ca²⁺ handling were determined. Results In isolated atrial trabeculae of diabetic myocardium the rise of systolic Ca²⁺ was significantly prolonged, but relaxation of the Ca²⁺ transient was unaltered compared to control tissue. Accordingly, the levels of expression of mRNA and protein of the Ca²⁺ release channel (RyR2) of the sarcoplasmic reticulum were reduced by 68 and 22%, respectively. Endogenous phosphorylation of RyR2 by protein kinases C, however, was increased by 31% in diabetic myocardium, as assessed by the back-phosphorylation technique. Levels of expression of SERCA2 and phospholamban were unaltered between both groups. Conclusions Intracellular Ca²⁺ release is prolonged in non-failing myocardium of type 2 diabetic patients and this may be primarily due to a decreased expression of RyR2. This defective Ca²⁺ release may represent an early stage of ventricular dysfunction in type 2 diabetes and would favor the abnormal response to exercise frequently observed in asymptomatic diabetic patients.     

A simple device to apply equibiaxial strain to cells cultured on flexible membranes

The biomechanical environment to which cells are exposed is important to their normal growth, development, interaction, and function. Accordingly, there has been much interest in studying the role of biomechanical forces in cell biology and pathophysiology. This has led to the introduction and even commercialization of many experimental devices. Many of the early devices were limited by the heterogeneity of deformation of cells cultivated in different locations of the culture plate membranes and were also attached with complicated technical/electronic efforts resulting in a restriction of the reproducibility of these devices. The objective of this study was to design and build a simple device to allow the application of dose-dependent homogeneous equibiaxial static stretch to cells cultured on flexible silicone membranes to investigate biological and biomedical questions. In addition, cultured neonatal rat atrial cardiomyocytes were stretched with the proposed device with different strain gradients. For the first time with this study we could demonstrate that stretch up to 21% caused dose-dependent changes in biological markers such as the calcineurin activity, modulatory calcineurin-interacting protein-1, voltage-gated potassium channel isoform 4.2, and voltage-gated K(+) channel-interacting proteins-2 gene expression and transient outward potassium current densities but not the protein-to-DNA ratio and atrial natriuretic peptide mRNA. With both markers mentioned last, dose-dependent stretch alterations could only be achieved with stretch up to 13%. The simple and low-cost device presented here might be applied to a wide range of experimental settings in different fields of research.     

Species richness,alien species and plant traits in Central Argentine mountain grasslands

Abstract. Pattern of native vegetation, distribution of alien species and variation of environmental parameters were studied in mountain grasslands in a lithologically homogeneous Córdoba mountain range in Central Argentina. CCA showed that altitude was the most important factor determining the compositional variation of the vegetation, with soil nutrient status and stoniness as additional factors. Short‐grass communities, associated with the driest habitats on plateaus, showed higher small‐scale native species richness than wet‐turf communities in valleys and tall‐grass communities on slopes. Species richness was negatively correlated with soil parameters that indicate nutrient status and water availability. Also, there was a negative correlation between soil Ca‐ and Mg‐ content and richness. High native species richness coincided with high alien species richness. When smaller units – community types – were considered, it became evident that within short‐grass vegetation, the three most species‐rich community types contained significant numbers of alien species, while the other two did not. Even within one community type, the same quadrats that contained the highest number of native species, were also characterized by the highest numbers of alien species. Evidently, the same mechanism was responsible for high richness of both native and alien species. Alien species were distinguished by a greater proportion of annuals and prostrate stoloniferous plants, by lower palatability and by smaller proportion of zoochory. DCA ordination of quadrats on the basis of plant traits as attributes resulted in a clear distinction of three main vegetation types. Short‐grass vegetation was distinguished by a predomination of late flowering species, tall‐grass vegetation by the presence of high herbaceous plants and bushes, and wet‐turf vegetation by the presence of plants with storage organs, the lack of hairy leaves, and by a high proportion of cryptophytes. Quadrats with and without alien species were distinguished as well, indicating that the occurrence of aliens may be dependent on plant traits in a particular patch of a community.