Composition and reactivity of DOC in forest floor soil solutions in relation to tree species and soil type

Metal coordinating propertiesof DOC (dissolved organic carbon), and henceits influence on heavy metal release andmineral weathering, depend on the compositionand properties of DOC. Tree species producelitter with different chemical composition anddegradability, and these differences mightinfluence the composition and reactivity of DOCin soil solutions. Accordingly, analysis ofcomposition and reactivity of DOC in soilsolution samples collected by centrifugationfrom 16 forest soil O horizons from the fourtree species beech (Fagus sylvatica L.),oak (Quercus robur L.), grand fir (Abies grandis Lindl.), and Norway spruce (Picea abies (L.) Karst.) on two clayey and twosandy soils were carried out. The compositionand properties of DOC were determined bycapillary zone electrophoresis, acid-basetitration, Cu ion titration, total elementalanalysis, IR and UV spectroscopy, and metalrelease assays. Concentrations of DOC rangedfrom 20 to 163 mM with pH ranging from 4.6 to7.3. Norway spruce produced the highest DOCconcentration, and the lowest pH. Carbon inlow-molecular-weight aliphatic carboxylic acids(LACA) accounted for less than 6% of DOC withformic and acetic acids as the most abundantLACAs. The DOC was cation exchanged and protonsaturated to obtain comparable forms of DOC.Titratable carboxylic acid and phenolic groupswere in the range 51 to 82 and 20 to64 mmol·mol^–1 C, respectively, with fewerphenolic groups in grand fir DOC as the onlysignificant difference. Infrared spectra offreeze-dried DOC samples suggest low contentsof aromatic C in the DOC especially from grandfir stands. Stability constants, log K of Cu-DOC complexes, determined by Cu ion titrationof DOC samples with fitting of the data to atwo-site binding model, were in the range 5.63to 6.21 for the strong binding sites and 3.58to 4.10 for the weak sites, but with nosignificant effects of tree species or site.Freeze-dried DOC samples were found to consistof 41 to 45% C, 38 to 49% O, 4.4 to 5.4% Hand 1.2 to 2.0% N and C/N ratios in the range26 to 42. Reactivity of DOC in terms of releaserates of Cd, Cu and Fe cations from a soilsample (flow cell experiments) showed nosignificant differences among DOC samples fromdifferent tree species and soil types.Apparently, only minor differences occur inchemical composition and reactivity ofequivalent concentrations of DOC in forestfloor soil solutions irrespective of origin,i.e. four tree species and two soil types. Soilsolution pH and the concentration of DOCproduced by various tree species are thecritical parameters when distinguishing amongtree species in relation to heavy metal releaseand mineral weathering.     

Functional divergence of the circadian clock proteins in prokaryotes

Cyanobacteria are only prokaryotes known so far to have a circadian system. It may be based either on two (kaiB and kaiC) or three (kaiA, kaiB and kaiC) circadian genes. The homologs of two circadian proteins, KaiB and KaiC, form four major subfamilies (K1–K4) and also occur in some other prokaryotes. Using the likelihood-ratio tests, we studied a rate shift at the functional divergence of the proteins from the different subfamilies. It appears that only two of the subfamilies (K1 and K2) perform circadian functions. We identified in total 92 sites that have significantly different rates of evolution between the clades K1/K2 and K3/K4; 67 sites (15 in KaiB and 52 in KaiC) been evolving significantly slower in K1/K2 than the overall average for the entire sequence. Many critical sites are located in the identified functionally important motifs and regions, e.g. one of the Walker’s motif As, DXXG motif, and two KaiA-binding domains of KaiC. There are also 36 sites (~5%) with rate shift between K1 and K2. The rate shift at these sites may be related to the interaction with KaiA. Rate shift analyses have identified residues whose manipulation in the Kai proteins may lead to better understanding of their functions in the two different types of the cyanobacterial circadian system.     

Recurrent hybridisation events between Primula vulgaris,P. veris and P. elatior (Primulaceae,Ericales) challenge the species boundaries: using molecular markers to re‐evaluate morphological identifications

Three Primula species, Primula vulgaris, P. veris and P. elatior, have been objects of fascination for gardeners and botanists over several centuries. The species are able to hybridise, and where they co‐occur, hybrids are commonly found. In Denmark, Møns Klint on the island of Møn and Købelev Skov on Lolland are examples of localities where all three species occur and where the hybrids P. × digenea, the hybrid between P. vulgaris and P. elatior, and P. × polyantha, the hybrid between P. veris and P. vulgaris, can also be found. To investigate relationships between the species and their hybrids, we sampled 168 specimens from 10 geographical locations and subjected them to genetic analysis. The samples were also identified based on morphological traits: primarily inflorescense structure, the size, shape, colour and markings of corolla and leaf basis, leaf blade texture and hairiness. After identifying species‐specific SNPs in the Internal Transcribed Spacer sequence, these were used to resolve species and hybrid boundaries and status through a cleaved amplified polymorphic sequence assay. Polymorphisms in the chloroplast trnL sequence were used as a high‐throughput marker and used to determine the maternal parent of hybrids. Ten simple sequence repeat markers were applied to obtain further insight into the genetic makeup of the accessions using structure and Introgress, providing information of genetic variability within and between populations. Our results indicated that backcrossing of P. × digenea hybrids with parental species has occurred, and that many of the P. × digenea sampled were later‐generation hybrids rather than F₁s. Analyses of P. × polyantha specimens show mostly the expected pattern for primary hybrids but indications of P. veris ancestry of a P. vulgaris plant was discovered. Our results further indicate that some of the specimens initially identified as P. elatior include P. vulgaris among their progenitors and thus challenge currently accepted species boundaries.     

A high-throughput method for genotyping S-RNase alleles in apple

We present a new efficient screening tool for detection of S-alleles in apple. The protocol using general and multiplexed primers for PCR reaction and fragment detection on an automatized capillary DNA sequencer exposed a higher number of alleles than any previous studies. Analysis of alleles is made on basis of three individual fragment sizes making the allele interpretation highly accurate. The method was employed to genotype 432 Malus accessions and exposed 25 different S-alleles in a selection of Malus domestica cultivars of mainly Danish origin (402 accessions) as well as a selection of other Malus species (30 accessions). The allele S3 (28 %) was the most common among the Danish cultivars followed by S1 and S7 (both 27 %). The alleles S36 and S40 not previously reported from M. domestica were found in 6 and 17 cultivars, respectively. Complete allelic composition was found in 91 % of the 369 diploid accessions and in 86 % of the 63 triploids concerned. We further identified a relatively high frequency of S33 and S34, which has not been considered by most previous studies. The protocol presented here is easy to adopt and saves both time and work effort compared to previous methods. The robustness is illustrated by the great accuracy and a high number of S-alleles presented.     

Molecular biology of distal muscular dystrophies--sarcomeric proteins on top

During the last 10 years several muscular dystrophies within the group of distal myopathies have been clarified as to the molecular genetic cause of the disease. Currently, the next steps are carried out to identify the molecular pathogenesis downstream of the gene defects. Some early ideas on what is going on in the muscle cells based on the defect proteins are emerging. However, in no single distal muscular dystrophy these efforts have yet reached the point where direct trials for therapy would have been launched, and in many distal dystrophies the causative gene is still lacking. When comparing the gene defects in the distal dystrophies with the more common proximal muscular dystrophies such as dystrophinopathies or limb-girdle muscular dystrophies, there is a striking difference: the genes for distal dystrophies encode sarcomere proteins whereas the genes for proximal dystrophies more often encode sarcolemmal proteins.     

The LKB1 tumor suppressor kinase in human disease

Inactivating germline mutations in the LKB1 gene underlie Peutz-Jeghers syndrome characterized by hamartomatous polyps and an elevated risk for cancer. Recent studies suggest the involvement of LKB1 also in more common human disorders including diabetes and in a significant fraction of lung adenocarcinomas. These observations have increased the interest towards signaling pathways of this tumor suppressor kinase. The recent breakthroughs in understanding the molecular functions of the LKB1 indicate its contribution as a regulator of cell polarity, energy metabolism and cell proliferation. Here we review how the substrates and cellular functions of LKB1 may be linked to Peutz-Jeghers syndrome and other diseases, and discuss how some of the molecular changes associated with altered LKB1 signaling might be used in therapeutic approaches.     

Low-molecular-weight aliphatic carboxylic acids in soil solutions under different vegetations determined by capillary zone electrophoresis

Concentrations of low-molecular-weight aliphatic carboxylic acids in soil solution were determined by a newly developed capillary zone electrophoresis method. Soil solution samples were collected by centrifugation of soil from the A horizon of a Danish, homogeneous, nutrient-rich Hapludalf in adjacent forested and arable plots. The forested plots of 0.5 ha were 33-year old stands of beech (Fagus sylvatica L.), oak (Quercus robur L.), grand fir (Abies grandis Lindl.), and Norway spruce (Picea abies (L.) Karst.), while sugar beet (Beta vulgaris L.) and winter wheat (Triticum aestivum L.) were the agricultural crops this year. High variability in soil solution concentrations of metal cations (Al, Ca, K, Mg, Na), monocarboxylic acids (formic, acetic, lactic, and valeric acids), and di- and tricarboxylic acids (oxalic, malic, succinic, and citric acids) were found within each plot. Despite this short-range within-plot variability, higher concentrations of di- and tricarboxylic acids were found in the forested soils than in the arable soils. The vegetation seemed to favour some monocarboxylic acids, but the total monocarboxylic acid concentrations showed little relation to the vegetation. Probably due to much less soil water in the Norway spruce plot, the low-molecular-weight aliphatic carboxylic acid concentrations in the samples from that plot were much higher than those found in samples from the other plots. Carbon in low-molecular-weight aliphatic carboxylic acids only accounts for a few percent of dissolved organic carbon, and no general relation was found between carbon in low-molecular-weight aliphatic carboxylic acids and dissolved organic carbon, although the correlation between carbon in di- and tricarboxylic acids and dissolved organic carbon was significant. This revised version was published online in June 2006 with corrections to the Cover Date.     

Organellar and Cytosolic Localization of Four Phosphoribosyl Diphosphate Synthase Isozymes in Spinach

We report on the efficacy of proteinase inhibitors (PIs) from three host plants (chickpea [Cicer arietinum], pigeonpea [Cajanus cajan], and cotton [Gossypium arboreum]) and three non-host (groundnut [Arachis hypogea], winged bean [Psophocarpus tetragonolobus], and potato [Solanum tuberosum]) in retarding the growth of Helicoverpa armigera larvae, a devastating pest of important crop plants. Enzyme assays and electrophoretic analysis of interaction of H. armigera gut proteinases (HGPs) with PIs revealed that non-host PIs inhibited HGP activity efficiently whereas host PIs were ineffective. In the electrophoretic assay, trypsin inhibitor activity bands were detected in all of the host and non-host plants, but HGP inhibitor activity bands were present only in non-host plants (except cotton in the host plant group). H. armigera larvae reared on a diet containing non-host PIs showed growth retardation, a reduction in total and trypsin-like proteinase activity, and the production of inhibitor-insensitive proteinases. Electrophoretic analysis of PI-induced HGP showed differential regulation of proteinase isoforms. Interestingly, HGP activity induced in response to dietary potato PI-II was inhibited by winged bean PIs. The optimized combination of potato PI-II and winged bean PIs identified in the present study and their proposed successive use has potential in developing H. armigera-resistant transgenic plants.