Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake

Bethlenfalvay, G. J., Brown, M. S., Ames, R. N. and Thomas, R. S. 1988. Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake. - Physiol. Plant. 72: 565–571.
Soybean [ Glycine max (L.) Merr.] plants were grown in pot cultures and inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe or provided with P fertilizer (non-VAM plants). After an initial growth period (21 days), plants were exposed to cycles of severe, moderate or no drought stress over a subsequent 28-day period by rewatering at soil water potentials of -1.0, -0.3 or -0.05 MPa. Dry weights of VAM plants were greater at severe stress and smaller at no stress than those of non-VAM plants. Phosphorus fertilization was applied to produce VAM and non-VAM plants of the same size at moderate stress. Root and leaf P concentrations were higher in non-VAM plants at all stress levels. All plants were stressed to permanent wilting prior to harvest. VAM plants had lower soil moisture content at harvest than non-VAM plants. Colonization of roots by G. mosseae did not vary with stress, but the biomass and length of the extraradical mycelium was greater in severely stressed than in non-stressed plants. Growth enhancement of VAM plants relative to P-fertilized non-VAM plants under severe stress was attributed to increased uptake of water as well as to more efficient P uptake. The ability of VAM plants to deplete soil water to a greater extent than non-VAM plants suggests lower permanent wilting potentials for the former.     

Rooting strategy of naturally regenerated beech in Silver birch and Scots pine woodlands

This study investigated the belowground development and strategy of late-successional European beech (Fagus sylvatica L.) in ageing natural Scots pine (Pinus sylvestris L.) and Silver birch (Betula pendula Roth.) woodlands in a French volcanic mid-elevation area. For this purpose root biomass, root profile and fine-root architecture of competitor trees were examined in 53 mixed pine–beech and 42 birch–beech woodlands along a stand maturation gradient, using the root auger technique (0–75-cm). The total beech fine-root biomass highly correlated with aerial dimensions such as stem height and girth, whereas it moderately correlated with its age, thus indicating the effects of competition. Basic stand biometric data such as stand density and basal area had no significant effect on beech root biomass. Conversely, competition indices taking into account the vertical dimensions of competitor trees were efficient, probably due to redundancy with beech height. At similar age and height, beeches under birch had a greater belowground development than beeches under pine. Each species exhibited specific rooting pattern and plasticity of fine-root architecture along the gradients of stand maturation and competition. Beech had a heart-shaped rooting habit in both mixings, which strongly increased along stand maturation. Its fine-root system adopted a foraging strategy to respond to increasing stand competition. The Scots pine fine-root system was plate-like and showed a low morphological plasticity, thus presumably a conservative strategy. Silver birch exhibited a high biomass and a foraging capacity in the topsoil but a loose root system in the subsoil. The coexistence of pine and beech roots in the upper soil presumably leads to a high belowground competition. Beech root system becomes predominant throughout the soil profile and it adopts an efficient foraging strategy, but at the expense of its belowground development. Conversely, the niche partitioning strategy between beech and birch may explain why beech develops strongly belowground in spite of the fact that birch has a dense rooting and a competitive fine-root architecture. As a consequence, beech mid-term regeneration and development may be facilitated under birch as compared with pine.     

The plant invertase inhibitor shares structural properties and disulfide bridges arrangement with the pectin methylesterase inhibitor

Attempts to purify the inhibitor of pectin methylesterase (PMEI) from the soluble extract of ripe apricot (Prunus armeniaca) fruit led to isolation of a protein (Pa-INH) similar to PMEI, but having invertase inhibitory activity against vacuolar invertase from tomato. The molecular charge, the native and SDS-PAGE molecular weights were similar to those of PMEI. Partial amino acid sequence indicated a high level of identity with invertase inhibitors and a significant identity with PMEI. Circular dichroism analysis showed a mainly -helix secondary structure for both the inhibitors and a higher thermostability of Pa-INH. Four Cys residues forming disulfide bridges in PMEI were conserved in Pa-INH. Similarly to PMEI, these residues were linked by disulfide bridges (first to second and third to fourth). The free Cys139 of PMEI is substituted by Ala in Pa-INH. The results reported in this study suggest a common structural arrangement of the two inhibitors.     

Underproduction of sigma 70 mimics a stringent response. A proteome approach

When Escherichia coli cells enter stationary phase due to carbon starvation the synthesis of ribosomal proteins is rapidly repressed. In a DeltarelA DeltaspoT mutant, defective in the production of the alarmone guanosine tetraphosphate (ppGpp), this regulation of the levels of the protein synthesizing system is abolished. Using a proteomic approach we demonstrate that the production of the vast majority of detected E. coli proteins are decontrolled during carbon starvation in the DeltarelA DeltaspoT strain and that the starved cells behave as if they were growing exponentially. In addition we show that the inhibition of ribosome synthesis by the stringent response can be qualitatively mimicked by artificially lowering the levels of the housekeeping sigma factor, sigma(70). In other words, genes encoding the protein-synthesizing system are especially sensitive to reduced availability of sigma(70) programmed RNA polymerase. This effect is not dependent on ppGpp since lowering the levels of sigma(70) gives a similar but less pronounced effect in a ppGpp(0) strain. The data is discussed in view of the models advocating for a passive control of gene expression during stringency based on alterations in RNA polymerase availability.     

Physical mapping of new DNA probes near the fragile X mutation (FRAXA) by using a panel of cell lines

The fragile X syndrome is a very common disorder, but there has been little progress toward isolating the fragile X mutation (FRAXA). We describe a panel of 14 somatic cell hybrid lines, lymphoblastoid cell lines, and peripheral lymphocytes with X-chromosome translocation or deletion breakpoints near FRAXA. The locations of the breakpoints were defined with 16 established probes between pX45d (DXS100) and St14-1 (DXS52). Seven of the cell lines had breakpoints between the probes RN1 (DXS369) and U6.2 (DXS304), which flank FRAXA at distances of 3-5 centimorgans. The panel of cell lines was used to localize 16 new DNA probes in this region. Six of the probes-VK16, VK18, VK23, VK24, VK37, and VK47--detected loci near FRAXA, and it was possible to order both the X-chromosome breakpoints and the probes in relation to FRAXA. The order of probes and loci near FRAXA is cen-RN1,VK24-VK47-VK23-VK16,FRAXA-++ +VK21A-VK18-IDS-VK37-U6.2-qter. The breakpoints near FRAXA are sufficiently close together that probes localized with this panel can be linked on a large-scale restriction map by pulsed-field gel electrophoresis. This panel of cell lines will be valuable in rapidly localizing other probes near FRAXA.     

Sperm deliver a new second messenger: NAADP

NAADP is a highly potent mobilizer of Ca(2+), which in turn triggers Ca(2+)-induced Ca(2+) release pathways in a wide range of species. Nevertheless, NAADP is not presently classified as a second messenger because it has not been shown to increase in response to a physiological stimulus. We now report a dramatic increase in NAADP during sea urchin egg fertilization that was largely due to production in sperm upon contacting egg jelly. The NAADP bolus plays a physiological role upon delivery to the egg based on its ability to induce a cortical flash, a depolarization-induced activation of L-type Ca(2+) channels. Moreover, the sperm-induced cortical flash was eliminated in eggs desensitized to NAADP. We conclude that an NAADP increase plays a physiologically relevant role during fertilization and provides the first conclusive demonstration that NAADP is a genuine second messenger.     

Lipid Domain Structure of the Plasma Membrane Revealed by Patching of Membrane Components

Lateral assemblies of glycolipids and cholesterol, “rafts,” have been implicated to play a role in cellular processes like membrane sorting, signal transduction, and cell adhesion. We studied the structure of raft domains in the plasma membrane of non-polarized cells. Overexpressed plasma membrane markers were evenly distributed in the plasma membrane. We compared the patching behavior of pairs of raft markers (defined by insolubility in Triton X-100) with pairs of raft/non-raft markers. For this purpose we cross-linked glycosyl-phosphatidylinositol (GPI)-anchored proteins placental alkaline phosphatase (PLAP), Thy-1, influenza virus hemagglutinin (HA), and the raft lipid ganglioside GM1 using antibodies and/or cholera toxin. The patches of these raft markers overlapped extensively in BHK cells as well as in Jurkat T–lymphoma cells. Importantly, patches of GPI-anchored PLAP accumulated src-like protein tyrosine kinase fyn, which is thought to be anchored in the cytoplasmic leaflet of raft domains. In contrast patched raft components and patches of transferrin receptor as a non-raft marker were sharply separated. Taken together, our data strongly suggest that coalescence of cross-linked raft elements is mediated by their common lipid environments, whereas separation of raft and non-raft patches is caused by the immiscibility of different lipid phases. This view is supported by the finding that cholesterol depletion abrogated segregation. Our results are consistent with the view that raft domains in the plasma membrane of non-polarized cells are normally small and highly dispersed but that raft size can be modulated by oligomerization of raft components.     

Extending the family of UNCG-like tetraloop motifs: NMR structure of a CACG tetraloop from coxsackievirus B3

Stable RNA tetraloop motifs are found frequently in biologically active RNAs. These motifs carry out a wide variety of functions in RNA folding, in RNA-RNA and RNA-protein interactions. A great deal of knowledge about the structures and functions of tetraloop motifs has accumulated largely due to intensive theoretical, biochemical, and biophysical studies on three most frequently occurring families of tetraloop sequences, namely, the cUNCGg, the cGNRAg, and the gCUUGc sequences. Our knowledge surely is not exhaustive, and efforts are still being made to gain a better understanding. Here we report the NMR structure of a uCACGg tetraloop that occurs naturally within the cloverleaf RNA structure of the 5'-UTR of coxsackievirus B3. This tetraloop is the major determinant for interaction between the cloverleaf RNA and viral 3C protease, which is an essential part of a ribonucleoprotein complex that plays a critical role in the regulation of viral translation and replication. Our structure shows that the CACG tetraloop is closed by a wobble U.G base pair. The structure of the CACG tetraloop is stabilized by extensive base stacking and hydrogen bonding interactions strikingly similar to those previously reported for the cUUCGg tetraloop. Identification of these hallmark structural features strongly supports the existence of an extended YNCG tetraloop family. The U.G base pair closing the stem and the A residue in the loop introduce some small structural and themodynamic distinctions from the canonical cUUCGg tetraloop that may be important for recognition by the viral 3C protease.     

High-resolution SNP scan of chromosome 6p21 in pooled samples from patients with complex diseases

We apply a high-throughput protocol of chip-based mass spectrometry (matrix-assisted laser desorption/ionization time-of-flight; MALDI-TOF) as a method of screening for differences in single-nucleotide polymorphism (SNP) allele frequencies. Using pooled DNA from individuals with asthma, Crohn's disease (CD), schizophrenia, type 1 diabetes (T1D), and controls, we selected 534 SNPs from an initial set of 1435 SNPs spanning a 25-Mb region on chromosome 6p21. The standard deviations of measurements of time of flight at different dots, from different PCRs, and from different pools indicate reliable results on each analysis step. In 90% of the disease-control comparisons we found allelic differences of <10%. Of the T1D samples, which served as a positive control, 10 SNPs with significant differences were observed after taking into account multiple testing. Of these 10 SNPs, 5 are located between DQB1 and DRB1, confirming the known association with the DR3 and DR4 haplotypes whereas two additional SNPs also reproduced known associations of T1D with DOB and LTA. In the CD pool also, two earlier described associations were found with SNPs close to DRB1 and MICA. Additional associations were found in the schizophrenia and asthma pools. They should be confirmed in individual samples or can be used to develop further quality criteria for accepting true differences between pools. The determination of SNP allele frequencies in pooled DNA appears to be of value in assigning further genotyping priorities also in large linkage regions.