Influence of leaf trichomes on boundary layer conductance and gas‐exchange characteristics in Metrosideros polymorpha (Myrtaceae)

The amount of trichomes on the leaves of Metrosideros polymorpha varies enormously, ranging from 0 to ca 150 g/m² across environmental gradients on the island of Hawaii. Pubescent individuals are abundant in dry areas or on young lava flows, whereas glabrous individuals are abundant in wet areas or on developed soils. To understand the adaptive advantages of pubescent individuals in arid environments, we addressed the following questions: (1) whether leaf trichomes increase the boundary layer resistance to gas diffusion, which in turn reduces the transpiration rate and increases water‐use efficiency (WUE); and (2) whether pubescent individuals have other associated leaf and shoot traits that have adaptive significance in arid environments. We made detailed ecophysiological measurements on M. polymorpha in three populations in habitats that varied in aridity. We found a large allocation of leaf mass to trichomes, up to 33 percent at the arid site, but our analyses showed that trichomes had small effects (1–9%) on gas exchange and negligible effects on WUE, suggesting the trichomes may have roles beyond increasing WUE. However, pubescent individuals did have higher Rubisco amount and a lower leaf‐to‐ sapwood area ratio, which are considered adaptive in arid environments. These results suggest that pubescent individuals of M. polymorpha are indeed adapted to arid environments with changes in a suite of traits. The adaptive significance of the enormous variation in amounts of trichomes remains unclear and may be related to functions other than increasing boundary layer resistance.     

Human Immunodeficiency Virus Type 1 Enhancer-binding Protein 3 Is Essential for the Expression of Asparagine-linked Glycosylation 2 in the Regulation of Osteoblast and Chondrocyte Differentiation

Human immunodeficiency virus type 1 enhancer-binding protein 3 (Hivep3) suppresses osteoblast differentiation by inducing proteasomal degradation of the osteogenesis master regulator Runx2. In this study, we tested the possibility of cooperation of Hivep1, Hivep2, and Hivep3 in osteoblast and/or chondrocyte differentiation. Microarray analyses with ST-2 bone stroma cells demonstrated that expression of any known osteochondrogenesis-related genes was not commonly affected by the three Hivep siRNAs. Only Hivep3 siRNA promoted osteoblast differentiation in ST-2 cells, whereas all three siRNAs cooperatively suppressed differentiation in ATDC5 chondrocytes. We further used microarray analysis to identify genes commonly down-regulated in both MC3T3-E1 osteoblasts and ST-2 cells upon knockdown of Hivep3 and identified asparagine-linked glycosylation 2 (Alg2), which encodes a mannosyltransferase residing on the endoplasmic reticulum. The Hivep3 siRNA-mediated promotion of osteoblast differentiation was negated by forced Alg2 expression. Alg2 suppressed osteoblast differentiation and bone formation in cultured calvarial bone. Alg2 was immunoprecipitated with Runx2, whereas the combined transfection of Runx2 and Alg2 interfered with Runx2 nuclear localization, which resulted in suppression of Runx2 activity. Chondrocyte differentiation was promoted by Hivep3 overexpression, in concert with increased expression of Creb3l2, whose gene product is the endoplasmic reticulum stress transducer crucial for chondrogenesis. Alg2 silencing suppressed Creb3l2 expression and chondrogenesis of ATDC5 cells, whereas infection of Alg2-expressing virus promoted chondrocyte maturation in cultured cartilage rudiments. Thus, Alg2, as a downstream mediator of Hivep3, suppresses osteogenesis, whereas it promotes chondrogenesis. To our knowledge, this study is the first to link a mannosyltransferase gene to osteochondrogenesis.     

Patterns of natural 15N abundance in the leaf-to-soil continuum of tropical rain forests differing in N availability on Mount Kinabalu,Borneo

We investigated the natural abundance of ¹⁵N in sun leaves and other components of tropical rain forests on altitudinal sequences of eight sites that form a gradient of soil N availability with varying ectomycorrhizal abundances on Mt. Kinabalu, Borneo. We investigated how soil N availability and ectomycorrhizal abundance related to the ¹⁵N abundance of ecosystem components. ¹⁵N values (¹⁵N abundance relative to ¹⁴N) increased consistently in the following order at each site: sun leaves, leaf litter, fine roots and from shallower organic to deeper mineral soil horizons. Enrichment (3–6 ¹⁵N) of ¹⁵N occurred at the litter–topsoil interface at all sites, and the magnitude of the enrichment correlated negatively with ¹⁵N depletion in the foliage, irrespective of ectomycorrhizal abundance. Foliar ¹⁵N values significantly positively correlated with their N concentrations. Foliar (and litter and root) ¹⁵N values correlated positively with NO₃ availability, and negatively with NH₄ availability. The two positive correlations of foliar ¹⁵N with foliar N and NO₃ availability were inconsistent with the assumption that stronger nitrification (hence a greater nitrate availability) produced a more ¹⁵N-depleted active inorganic N pool. The isotopic fractionation during the passage of N through ectomycorrhizas to plants might explain the positive correlation of foliar ¹⁵N and N concentration; however, this mechanism could not fully explain the correlation in our case because strong foliar ¹⁵N depletions occurred at the sites that lacked ectomycorrhizas. Alternatively, the positive correlation across sites reflected the tightness of N cycling. Strong nitrification and associated isotopic fractionation might have occurred at N-richer sites and the subsequent removal of NO₃ from the system could decrease isotopically `lighter' N at these sites.     

Environmental correlates of tree biomass, basal area, wood specific gravity and stem density gradients in Borneo's tropical forests

Aim Tropical forests have been recognized as important global carbon sinks and sources. However, many uncertainties about the spatial distribution of live tree above‐ground biomass (AGB) remain, mostly due to limited availability of AGB field data. Recent studies in the Amazon have already shown the importance of large sample size for accurate AGB gradient analysis. Here we use a large stem density, basal area, community wood density and AGB dataset to study and explain their spatial patterns in an Asian tropical forest. Location Borneo, Southeast Asia. Methods We combined stem density, basal area, community wood density and AGB data from 83 locations in Borneo with an environmental database containing elevation, climate and soil variables. The Akaike information criterion was used to select models and environmental variables that best explained the observed values of stem density, basal area, community wood density and AGB. These models were used to extrapolate these parameters across Borneo. Results We found that wood density, stem density, basal area and AGB respond significantly, but differentially, to the environment. AGB was only correlated with basal area, but not with stem density and community wood specific gravity. Main conclusions Unlike results from Amazonian forests, soil fertility was an important positive correlate for AGB in Borneo while community wood density, which is a main driver of AGB in the Neotropics, did not correlate with AGB in Borneo. Also, Borneo's average AGB of 457.1 Mg ha^?1 was c. 60% higher than the Amazonian average of 288.6 Mg ha^?1. We find evidence that this difference might be partly explained by the high density of large wind‐dispersed Dipterocarpaceae in Borneo, which need to be tall and emergent to disperse their seeds. Our results emphasize the importance of Bornean forests as carbon sinks and sources due to their high carbon storage capacity.     

Requirement for the p75 TNF-alpha receptor 2 in the regulation of airway hyperresponsiveness by gamma delta T cells

In a recent study, we found that TNF-alpha negatively regulates airway responsiveness through the activation of gammadelta T cells. The biological activities of TNF-alpha are mediated by two structurally related but functionally distinct receptors, p55 (TNFR1) and p75 (TNFR2), which are independently expressed on the cell surface. However, the relative importance of either TNFR in airway hyperresponsiveness (AHR) is unknown. To investigate the importance of these TNFRs in the development of allergen-induced AHR, p55-deficient and p75-deficient mice were sensitized to OVA by i.p. injection and subsequently challenged with OVA via the airways; airway responsiveness to inhaled methacholine was monitored. p75-deficient mice developed AHR to a similar degree as control mice. In contrast, p55-deficient mice, which were sensitized and challenged with OVA, failed to develop AHR. In p55-deficient mice, both the numbers of eosinophils and levels of IL-5 in bronchoalveolar lavage fluid were significantly lower than in sensitized/challenged control mice (p < 0.05). However, depletion of gammadelta T cells resulted in significant increases in AHR in the p55-deficient mice, whereas no significant effect of gammadelta T cell depletion was evident in the p75-deficient mice. These data indicate that, in the absence of TNFR1 (p55), where TNF-alpha uses the p75 pathway exclusively, the development of AHR is regulated by gammadelta T cells.     

Characterization of recombinant mouse epidermal-type transglutaminase (TGase 3): regulation of its activity by proteolysis and guanine nucleotides.

Epidermal-type TGase (TGase 3) is involved in the formation of the cornified cell envelope by cross-linking a variety of structural proteins in the epidermis. Unknown proteases activate this enzyme from the zymogen form by limited proteolysis during epidermal differentiation. It has been difficult to isolate sufficient quantities of native enzymes from tissues for biochemical studies of the properties of TGase 3. In this paper, we circumvented these problems by expressing recombinant full-length mouse TGase 3 in a baculovirus system, and purifying it to homogeneity by successive chromatography and HPLC. Treatment of the purified recombinant protein with dispase, a bacterial protease known to activate zymogens, produced activated TGase 3. The migration of TGase 3 zymogen in SDS-polyacrylamide gel electrophoresis was anomalous when the proTGase 3 was pre-incubated with calcium ion. GTP inhibited the enzymatic activity of recombinant TGase 3. Calpain, a calcium-dependent neutral protease, was a candidate protease, but had no effect on the activation of TGase 3 zymogen.     

Aboveground biomass and soil nutrient pools of a Scalesia pedunculata montane forest on Santa Cruz, Galápagos

We estimated the live aboveground biomass (AGB) and soil nutrient pools of the Scalesia pedunculata monodominant tropical montane forest at 600 m above sea level on Santa Cruz, Galápagos, an isolated oceanic island. The estimated AGB was 60.4 Mg ha^–1, which was considerably lower than that of other montane forests of similar climates elsewhere. Nutrient pools were ample for inorganic N, soluble P, and exchangeable cations. We suggest that the low AGB, in spite of the ample nutrients, is related to the absence of tall-statured climax species, that have high demands for nutrients (particularly N) to fix C, due to the isolation.     

Interspecific differences in the responses of root phosphatase activities and morphology to nitrogen and phosphorus fertilization in Bornean tropical rain forests

Soil organic phosphorus (P) compounds can be the main P source for plants in P‐limited tropical rainforests. Phosphorus occurs in diverse chemical forms, including monoester P, diester P, and phytate, which require enzymatic hydrolysis by phosphatase into inorganic P before assimilation by plants. The interactions between plant interspecific differences in organic P acquisition strategies via phosphatase activities with root morphological traits would lead to P resource partitioning, but they have not been rigorously evaluated. We measured the activities of three classes of phosphatases (phosphomonoesterase, PME; phosphodiesterase, PDE; and phytase, PhT), specific root length (SRL), root diameter, and root tissue density in mature tree species with different mycorrhizal associations (ectomycorrhizal [ECM] or arbuscular mycorrhizal [AM]) and different successional status (climax or pioneer species) in Sabah, Malaysia. We studied nitrogen (N)‐ and P‐fertilized plots to evaluate the acquisition strategies for organic P under P‐limited conditions 7 years after fertilization was initiated. P fertilization reduced the PME activity in all studied species and reduced PhT and PDE activities more in climax species than in the two pioneer species, irrespective of the mycorrhizal type. PDE activity increased in some climax species after N fertilization, suggesting that these species allocate excess N to the synthesis of PDE. Moreover, PME and PhT activities, but not PDE activity, correlated positively with SRL. We suggest that climax species tend to be more strongly dependent on recalcitrant organic P (i.e., phytate and/or diester P) than pioneer species, regardless of the mycorrhizal type. We also suggest that trees in which root PME or PhT activity is enhanced can increase their SRL to acquire P efficiently. Resource partitioning of soil organic P would occur among species through differences in their phosphatase activities, which plays potentially ecologically important role in reducing the competition among coexisting tree species in lowland tropical rainforests.     

Human hepatocyte growth factor promotes functional recovery in primates after spinal cord injury

Many therapeutic interventions for spinal cord injury (SCI) using neurotrophic factors have focused on reducing the area damaged by secondary, post-injury degeneration, to promote functional recovery. Hepatocyte growth factor (HGF), which is a potent mitogen for mature hepatocytes and a mediator of the inflammatory responses to tissue injury, was recently highlighted as a potent neurotrophic factor in the central nervous system. We previously reported that introducing exogenous HGF into the injured rodent spinal cord using a herpes simplex virus-1 vector significantly reduces the area of damaged tissue and promotes functional recovery. However, that study did not examine the therapeutic effects of administering HGF after injury, which is the most critical issue for clinical application. To translate this strategy to human treatment, we induced a contusive cervical SCI in the common marmoset, a primate, and then administered recombinant human HGF (rhHGF) intrathecally. Motor function was assessed using an original open field scoring system focusing on manual function, including reach-and-grasp performance and hand placement in walking. The intrathecal rhHGF preserved the corticospinal fibers and myelinated areas, thereby promoting functional recovery. In vivo magnetic resonance imaging showed significant preservation of the intact spinal cord parenchyma. rhHGF-treatment did not give rise to an abnormal outgrowth of calcitonin gene related peptide positive fibers compared to the control group, indicating that this treatment did not induce or exacerbate allodynia. This is the first study to report the efficacy of rhHGF for treating SCI in non-human primates. In addition, this is the first presentation of a novel scale for assessing neurological motor performance in non-human primates after contusive cervical SCI.     

The activities of soil and root acid phosphatase in the nine tropical rain forests that differ in phosphorus availability on Mount Kinabalu, Borneo

Background and aims

Tropical rain forests on deeply weathered soils are increasingly thought to be limited by phosphorus (P), where plants and associated organisms would demonstrate adaptations to efficiently recycle P using acid phosphatase from organic matter. The activities of soil and root acid phosphatase were investigated in nine tropical rain forests that demonstrated a 20-fold difference in the soil organic P pool on Mt. Kinabalu, Borneo.

Methods

Acid phosphatase activity was measured at pH6.0 using p-nitrophenyl phosphate as substrate.

Results

The specific phosphatase activity of tree roots on a soil-surface-area basis was significantly positively related with P-use efficiency of above-ground productivity, suggesting a physiological linkage between above and below-ground systems in the adaptation to P deficiency. The phosphatase activities of soils and roots were significantly negatively correlated with the pool size of soil organic P fractions, suggesting that demand for P determines phosphatase activities.

Conclusions

It is suggested that tree roots and soil microbes develop more active phosphatases in response to the chronic shortage of soil P, which forms the basis for an important functional role for the efficient acquisition of P from soil organic matter.