Rice husk and charred husk amendments increase porewater and plant Si but water management determines grain As and Cd concentration

Plant and Soil - Rice is a staple crop worldwide and a silicon (Si) hyperaccumulator with Si levels reaching 5–10% of its mass; this can result in desilication and Si-deficiency if plant...     

Expression and functional analysis of AtMUS81 in Arabidopsis meiosis reveals a role in the second pathway of crossing-over

Meiotic crossovers/chiasmata, that are required to ensure chromosome disjunction, arise via the class I interference-dependent pathway or via the class II interference-free pathway. The proportions of these two classes vary considerably between different organisms. In Arabidopsis, about 85% of chiasmata are eliminated in Atmsh4 mutants, denoting that these are class I events. In budding and fission yeasts Msh4-independent crossovers arise largely or entirely via a Mus81-dependent pathway. To investigate the origins of the 15% residual (AtMSH4-independent) chiasmata in Arabidopsis we conducted a cytological and molecular analysis of AtMUS81 meiotic expression and function. Although AtMUS81 functions in somatic DNA repair and recombination, it is more highly expressed in reproductive tissues. The protein is abundantly present in early prophase I meiocytes, where it co-localizes, in a double-strand break-dependent manner, with the recombination protein AtRAD51. Despite this, an Atmus81 mutant shows normal growth and has no obvious defects in reproductive development that would indicate meiotic impairment. A cytological analysis confirmed that meiosis was apparently normal in this mutant and its mean chiasma frequency was similar to that of wild-type plants. However, an Atmsh4 / Atmus81 double mutant revealed a significantly reduced mean chiasma frequency (0.85 per cell), compared with an Atmsh4 single mutant (1.25 per cell), from which we conclude that AtMUS81 accounts for some, but not all, of the 15% AtMSH4-independent residual crossovers. It is possible that other genes are responsible for these residual chiasmata. Alternatively the AtMUS81 pathway coexists with an alternative parallel pathway that can perform the same functions.     

Seasonal and diurnal variations in ultraviolet-B and ultraviolet-A irradiances at and below the sea surface at Helgoland (North Sea) over a 6-year period

Ultraviolet (UV) radiation at four wavelengths (305, 320, 340 and 380 nm) and photosynthetically active radiation (PAR) were measured from May 1994 to October 1999 using Biospherical UV radiometers. A surface reference sensor located on the roof of the Marine Station at Helgoland recorded values every 5 min, and an equivalent profiling underwater sensor was used for measurements in the sea at approximately monthly intervals. The ratio of 305-nm radiation to PAR varied seasonally, with a 14-fold increase from winter to summer. A much weaker seasonal trend (ca. 1.5-fold) was apparent in the ratio of 320-nm radiation to PAR, but there was no seasonal trend in the ratios of 340- or 380-nm radiation to PAR. The year-to-year variations in 305-nm radiation were also much greater relative to PAR than for the other UV wavelengths, but there was no evidence of a change in the 305 nm:PAR ratio over the study period. The ratios of both 305- and 320-nm radiation to PAR increased from dawn to midday, but those of 340- and 380-nm radiation were almost constant through the day, except shortly before sunrise and after sunset when the proportions of 340- and 380-nm radiation increased. Underwater measurements of PAR and UV suggest that the 1% depth for 305-nm radiation was little more than 1 m, but this estimate is valid only for summer and autumn because, in other seasons, few reliable readings for 305-nm radiation could be obtained underwater, and no attenuation coefficient could be calculated. The 1% depths recorded for the other UV wavelengths in the middle 6 months of the year were 2.0 m for 320 nm, 2.6 m for 340 nm and 4.6 m for 380 nm, compared with 12 m for PAR, but the attenuation of all wavebands increased sharply in October and remained higher until March. An analysis of the influence of sun angle, total column ozone concentration, the proportion of skylight, and cloud cover on the ratio of UV wavelengths to PAR in surface irradiance demonstrated that solar angle has a greater influence than ozone concentration on the irradiance at 305 nm, and that the typical occurrence of ozone "holes" in spring may not result in higher UV-B irradiances than occur under higher ozone concentrations in summer. The implications of the data for attempts to model the biological effects of natural UV radiation on marine organisms are considered. Received in revised form: 3 July 2000 Electronic Publication     

Suppression of programmed neuronal death by a thapsigargin-induced Ca2+ influx

Rat sympathetic neurons undergo programmed cell death (PCD) in vitro and in vivo when they are deprived of nerve growth factor (NGF). Chronic depolarization of these neurons in cell culture with elevated concentrations of extracellular potassium ([K⁺]_o) prevents this death. The effect of prolonged depolarization on neuronal survival is thought to be mediated by a rise of intracellular calcium concentration ([Ca²⁺]_i) caused by Ca²⁺ influx through voltage-gated channels. In this report we investigate the effects of chronic treatment of rat sympathetic neurons with thapsigargin, an inhibitor of intracellular Ca²⁺ sequestration. In medium containing a normal concentration of extracellular Ca²⁺ ([Ca²⁺]_o), thapsigargin caused a sustained rise of intracellular Ca²⁺ concentration and partially blocked death of NGF-deprived cells. Elevating [Ca²⁺]_o in the presence of thapsigargin further increased [Ca²⁺]_i, suggesting that the sustained rise of [Ca²⁺]_i was caused by a thapsigargin-induced Ca²⁺ influx. This treatment potentiated the effect of thapsigargin on survival. The dihydropyridine Ca²⁺ channel antagonist, nifedipine, blocked both a sustained elevation of [Ca²⁺]_i and enhanced survival caused by depolarization with elevated [K⁺]_o, suggesting that these effects are mediated by Ca²⁺ influx through L-type channels. Nifedipine did not block the sustained rise of [Ca²⁺]_i or enhanced survival caused by thapsigargin treatment, indicating that these effects were not mediated by influx of Ca²⁺ through L-type channels. These results provide additional evidence that increased [Ca²⁺]_i can suppress neuronal PCD and identify a novel method for chronically raising neuronal [Ca²⁺]_i for investigation of this and other Ca²⁺-dependent phenomena. © 1995 John Wiley & Sons, Inc.     

Pressure dissociation of integration host factor-DNA complexes reveals flexibility-dependent structural variation at the protein-DNA interface

E. coli Integration host factor (IHF) condenses the bacterial nucleoid by wrapping DNA. Previously, we showed that DNA flexibility compensates for structural characteristics of the four consensus recognition elements associated with specific binding (Aeling et al., J. Biol. Chem. 281, 39236–39248, 2006). If elements are missing, high-affinity binding occurs only if DNA deformation energy is low. In contrast, if all elements are present, net binding energy is unaffected by deformation energy. We tested two hypotheses for this observation: in complexes containing all elements, (1) stiff DNA sequences are less bent upon binding IHF than flexible ones; or (2) DNA sequences with differing flexibility have interactions with IHF that compensate for unfavorable deformation energy. Time-resolved Förster resonance energy transfer (FRET) shows that global topologies are indistinguishable for three complexes with oligonucleotides of different flexibility. However, pressure perturbation shows that the volume change upon binding is smaller with increasing flexibility. We interpret these results in the context of Record and coworker's model for IHF binding (J. Mol. Biol. 310, 379–401, 2001). We propose that the volume changes reflect differences in hydration that arise from structural variation at IHF–DNA interfaces while the resulting energetic compensation maintains the same net binding energy.     

Schistosoma mansoni: SmLIMPETin, a member of a novel family of invertebrate-only regulatory proteins

Eukaryotic LIM domain proteins contain zinc finger forming motifs rich in cysteine and histidine that enable them to interact with other proteins. A cDNA clone isolated from an adult schistosome cDNA library revealed a sequence that coded for a novel class of proteins bearing 6 LIM domains and an N-terminal PET domain, SmLIMPETin. Phylogeny reconstruction of SmLIMPETin and comparison of its sequence to invertebrate homologues and to the vertebrate four-and-a-half LIM domains protein family (FHLs), uncovered a novel LIM domain protein family, the invertebrate LIM and PET domain protein family (LIMPETin). Northern blots, RT-PCR and Western blot showed that SmLIMPETin gene was less expressed in sexually mature adult females compared to sexually immature adult females and sexually mature and immature adult males, and not expressed in schistosomula.