Contribution of amino compounds to dissolved organic nitrogen in forest soils

Dissolved organic nitrogen (DON) may play an important role in plantnutrition and nitrogen fluxes in forest ecosystems. In spite of the apparentimportance of DON, there is a paucity of information concerning its chemicalcomposition. However, it is exactly this chemical characterization that isrequired to understand the importance of DON in ecosystem processes. Theprimaryobjective of this study was to characterize the distribution of free aminoacidsand hydrolyzable peptides/proteins in the DON fraction of Oa horizon leachatesalong an extreme edaphic gradient in northern California. Insitu soil solutions were extracted by centrifugation from Oahorizonscollected beneath Pinus muricata (Bishop pine) andCupressus pygmaea (pygmy cypress) on slightlyacidic/fertile and highly acidic/infertile sites. DON accounted for 77 to99% of the total dissolved nitrogen in Oa horizon leachates. Nitrogen infree amino acids and alkyl amines ranged from 0.04–0.07 mgN/L on the low fertility site to 0.45–0.49 mg N/L onthe high fertility site, and accounted for 1.5 to 10.6% of the DON fraction.Serine, glutamic acid, leucine, ornithine, alanine, aspartic acid andmethylamine were generally the most abundant free amino compounds. Combinedamino acids released by acid hydrolysis accounted for 48 to 74% of theDON, suggesting that proteins and peptides were the main contributor to DON inOa horizon leachates. Together, nitrogen from free andcombined amino compounds accounted for 59 to 78% of the DON. Most of theDON was found in the hydrophobic fraction, which suggests the presence ofprotein/peptide-polyphenol complexes or amino compounds associated withhumic substances. Because free and combined amino acids can be an importantnitrogen source for some plants, soil DON may play an important role in plantnutrition and ecosystem function.     

An acylatable residue of Hedgehog is differentially required in Drosophila and mouse limb development

The Drosophila Hedgehog protein and its vertebrate counterpart Sonic hedgehog are required for a wide variety of patterning events throughout development. Hedgehog proteins are secreted from cells and undergo autocatalytic cleavage and cholesterol modification to produce a mature signaling domain. This domain of Sonic hedgehog has recently been shown to acquire an N-terminal acyl group in cell culture. We have investigated the in vivo role that such acylation might play in appendage patterning in mouse and Drosophila; in both species Hedgehog proteins define a posterior domain of the limb or wing. A mutant form of Sonic hedgehog that cannot undergo acylation retains significant ability to repattern the mouse limb. However, the corresponding mutation in Drosophila Hedgehog renders it inactive in vivo, although it is normally processed. Furthermore, overexpression of the mutant form has dominant negative effects on Hedgehog signaling. These data suggest that the importance of the N-terminal cysteine of mature Hedgehog in patterning appendages differs between species.     

Regulation of poly(ADP-ribose) polymerase-1-dependent gene expression through promoter-directed recruitment of a nuclear NAD+ synthase

NMNAT-1 and PARP-1, two key enzymes in the NAD(+) metabolic pathway, localize to the nucleus where integration of their enzymatic activities has the potential to control a variety of nuclear processes. Using a variety of biochemical, molecular, cell-based, and genomic assays, we show that NMNAT-1 and PARP-1 physically and functionally interact at target gene promoters in MCF-7 cells. Specifically, we show that PARP-1 recruits NMNAT-1 to promoters where it produces NAD(+) to support PARP-1 catalytic activity, but also enhances the enzymatic activity of PARP-1 independently of NAD(+) production. Furthermore, using two-photon excitation microscopy, we show that NMNAT-1 catalyzes the production of NAD(+) in a nuclear pool that may be distinct from other cellular compartments. In expression microarray experiments, depletion of NMNAT-1 or PARP-1 alters the expression of about 200 protein-coding genes each, with about 10% overlap between the two gene sets. NMNAT-1 enzymatic activity is required for PARP-1-dependent poly(ADP-ribosyl)ation at the promoters of commonly regulated target genes, as well as the expression of those target genes. Collectively, our studies link the enzymatic activities of NMNAT-1 and PARP-1 to the regulation of a set of common target genes through functional interactions at target gene promoters.     

Temperature determines the occurrence of CAM or C<Subscript>3</Subscript> photosynthesis in pineapple plantlets grown <Emphasis Type="Italic">in vitro</Emphasis>

Summary Ananas comosus (L.) Merr. var. Smooth Cayenne plants when grown in vitro under different temperature regimes developed as CAM or as C₃ plants. The plants used in this study were developed from the lateral buds of the nodal etiolated stem explants cultured on Murashige and Skoog medium for 3 mo. The cultures were maintained under a 16-h photoperiod for different thermoperiods. With 28°C light/15°C dark thermoperiod, as compared with constant 28°C light and dark, pineapple plants had a succulence index two times greater, and also a greater nocturnal titratable acidity and phosphoenolpyruvate carboxylase (PEPCase) activity, indicating CAM-type photosynthesis. The highest abscisic acid (ABA) level occurred during the light period, 8 h prior to maximum PEPCase activity, while the indole-3-acetic acid (IAA) peak was found during the dark period, coinciding with the time of highest PEPCase activity. These plants were also smaller with thicker leaves and fewer roots, but had greater dry weight. Their leaves showed histological characteristics of CAM plants, such as the presence of greater quantities of chlorenchyma and hypoderm. In addition, their vascular system was more conspicuous. In contrast, under constant temperature (28°C light/dark) plants showed little succulence in the leaves. There was no significant acid oscillation and diurnal variation in PEPCase activity in these plants, suggesting the occurrence of C₃ photosynthesis. Also, no diurnal variation in ABA and IAA contents was observed. The results of this study clearly indicate a role for temperature in determining the type of carbon fixation pathway in in vitro grown pineapple. Evidence that ABA and IAA participate in CAM signaling is provided.     

Fasting induces basolateral uptake transporters of the SLC family in the liver via HNF4alpha and PGC1alpha

Fasting induces numerous adaptive changes in metabolism by several central signaling pathways, the most important represented by the HNF4alpha/PGC-1alpha-pathway. Because HNF4alpha has been identified as central regulator of basolateral bile acid transporters and a previous study reports increased basolateral bile acid uptake into the liver during fasting, we hypothesized that HNF4alpha is involved in fasting-induced bile acid uptake via upregulation of basolateral bile acid transporters. In rats, mRNA of Ntcp, Oatp1, and Oatp2 were significantly increased after 48 h of fasting. Protein expression as determined by Western blot showed significant increases for all three transporters 72 h after the onset of fasting. Whereas binding activity of HNF1alpha in electrophoretic mobility shift assays remained unchanged, HNF4alpha binding activity to the Ntcp promoter was increased significantly. In line with this result, we found significantly increased mRNA expression of HNF4alpha and PGC-1alpha. Functional studies in HepG2 cells revealed an increased endogenous NTCP mRNA expression upon cotransfection with either HNF4alpha, PGC-1alpha, or a combination of both. We conclude that upregulation of the basolateral bile acid transporters Ntcp, Oatp1, and Oatp2 in fasted rats is mediated via the HNF4alpha/PGC-1alpha pathway.