ARABIDILLO proteins have a novel and conserved domain structure important for the regulation of their stability

ARABIDILLO proteins are F-box-Armadillo (ARM) proteins that regulate root branching in Arabidopsis. Many F-box proteins in plants, yeast and mammals are unstable. In plants, the mechanism for this instability has not been fully investigated. Here, we show that a conserved family of plant ARABIDILLO-related proteins has a unique domain structure consisting of an F-box and leucine-rich repeats (LRRs) followed by ARM-repeats. The LRRs are similar to those found in other plant and animal F-box proteins, including cell cycle proteins and hormone receptors. We demonstrate that the LRRs are required for ARABIDILLO1 function in vivo. ARABIDILLO1 protein is unstable: we show that ARABIDILLO1 protein is associated with ubiquitin and is turned over by the proteasome. Both the F-box and LRR regions of ARABIDILLO1 appear to enable this turnover to occur. Application of known lateral root-regulating signals has no effect on ARABIDILLO1 stability. In addition, plants that lack or overexpress ARABIDILLO proteins respond normally to known lateral root-regulating signals. Thus, we suggest that the signal(s) regulating ARABIDILLO stability in vivo may be either highly specific or novel. The structural conservation between ARABIDILLOs and other plant and animal F-box proteins suggests that the stability of other F-box proteins may be controlled by similar mechanisms.     

Regreening in spathes of Zantedeschia after anthesis: its physiology and control by fructification and hormones

The mature pigmented spathe of Zantedeschia is characterized by a developmental process, wherein the spathe regreens after anthesis and prior to senescence of the inflorescence. Previous research has shown that spathe regreening involves redifferentiation of chloroplasts and re‐accumulation of chlorophyll, but the detailed physiological changes associated with regreening are still largely unknown. Using Zantedeschia aethiopica and the Zantedeschia pentlandii variety ‘Best Gold’ as models, this study explores the physiological mechanism and possible roles of fructification, 6‐benzylaminopurine (BAP) and gibberellin (GA₃) in induction or progression of spathe regreening. Application of BAP stimulated regreening in spathe tissue of ‘Best Gold’ by enhancing accumulation of carotenoid and chlorophyll, and also increasing stacking of grana. In contrast, GA₃ retarded formation of double‐membrane lamella during chloroplast redifferentiation, thus delaying the onset of regreening. We suggest that these actions of BAP and GA₃ have a synergistic effect in delaying the onset of regreening in ‘Best Gold’ so that when applied together retardation of chlorophyll accumulation, chloroplast redifferentiation and accumulation of carotenoids were enhanced. The elimination of fructification did not prevent the occurrence of regreening in either Zantedeschia model plants, indicating that fructification was not a prerequisite for the induction of regreening. It is still unclear how regreening in Zantedeschia is triggered. We propose that the onset of regreening in Zantedeschia is likely to be a genetically programmed event.     

Genetic consequences of habitat fragmentation and loss: the case of the Florida black bear (<Emphasis Type="Italic">Ursus americanus floridanus</Emphasis>)

Habitat loss and fragmentation can influence the genetic structure of biological populations. We studied the genetic consequences of habitat fragmentation in Florida black bear (Ursus americanus floridanus) populations. Genetic samples were collected from 339 bears, representing nine populations. Bears were genotyped for 12 microsatellite loci to estimate genetic variation and to characterize genetic structure. None of the nine study populations deviated from Hardy–Weinberg equilibrium. Genetic variation, quantified by mean expected heterozygosity (H _E), ranged from 0.27 to 0.71 and was substantially lower in smaller and less connected populations. High levels of genetic differentiation among populations (global F _ST = 0.224; global R _ST = 0.245) suggest that fragmentation of once contiguous habitat has resulted in genetically distinct populations. There was no isolation-by-distance relationship among Florida black bear populations, likely because of barriers to gene flow created by habitat fragmentation and other anthropogenic disturbances. These factors resulted in genetic differentiation among populations, even those that were geographically close. Population assignment tests indicated that most individuals were genetically assigned to the population where they were sampled. Habitat fragmentation and anthropogenic barriers to movement appear to have limited the dispersal capabilities of the Florida black bear, thereby reducing gene flow among populations. Regional corridors or translocation of bears may be needed to restore historical levels of genetic variation. Our results suggest that management actions to mitigate genetic consequences of habitat fragmentation are needed to ensure long-term persistence of the Florida black bear.     

Detection of Schistosoma mansoni eggs in feces through their interaction with paramagnetic beads in a magnetic field

Background

Diagnosis of intestinal schistosomiasis in low endemic areas is a problem because often control measures have reduced egg burdens in feces to below the detection limits of classical coproparasitological methods. Evaluation of molecular methods is hindered by the absence of an established standard with maximum sensitivity and specificity. One strategy to optimize method performance, where eggs are rare events, is to examine large amounts of feces. A novel diagnostic method for isolation of Schistosoma mansoni eggs in feces, and an initial evaluation of its performance is reported here.

Methodology/Principal Findings

Known amounts of S. mansoni eggs were seeded into 30 g of normal human feces and subjected to a sequence of spontaneous sedimentation, sieving, Ritchie method, incubation and isolation through interaction with paramagnetic beads. Preliminary tests demonstrated the efficacy of lectins as ligands, but they also indicated that the paramagnetic beads alone were sufficient to isolate the eggs under a magnetic field through an unknown mechanism. Eggs were identified by microscopic inspection, with a sensitivity of 100% at 1.3 eggs per gram of feces (epg). Sensitivity gradually decreased to 25% at a concentration of 0.1 epg. In a preliminary application of the new method to the investigation of a recently established focus in southern Brazil, approximately 3 times more eggs were detected than with the thick-smear Kato-Katz method.

Conclusions/Significance

The novel S. mansoni detection method may significantly improve diagnosis of infections with low burdens in areas of recent introduction of the parasite, areas under successful control of transmission, or in infected travelers. It may also improve the evaluation of new treatments and vaccines.     

Suppressing expression of a soluble acid invertase (BoINV2) in broccoli (Brassica oleracea) delays postharvest floret senescence and downregulates cysteine protease (BoCP5) transcription

We report on the production and selection of transgenic Brassica oleracea var. Italica lines with a downregulated soluble acid invertase ( BoINV2 ). Explants of broccoli (cv. Triathlon) were transformed with an antisense construct of BoINV2 under the control of an Asparagus officinalis -derived harvest-induced promoter using Agrobacterium tumefaciens -mediated transformation. BoINV2 is upregulated in wild-type broccoli floret tissue after harvest. Transgenic broccoli lines showed reduced BoINV2 mRNA accumulation immediately after harvest compared with wild-type. Downregulation of BoINV2 had no significant impact on the expression of a second broccoli acid invertase gene ( BoINV1 ), but plants with downregulated BoINV2 also had lower expression of a senescence-associated cysteine protease ( BoCP5 ) compared with wild-type. The total soluble sugar levels in floret tissue of antisense BoINV2 lines were greater than wild-type tissue after harvest (up to 1.5 times higher). Soluble protein content of wild-type tissue decreased from 48 h after harvest with an increase in protease activity. In comparison, two antisense BoINV2 lines retained at-harvest levels of soluble protein until 72 and 96 h after harvest and had lower postharvest endoprotease activity compared with wild-type. Antisense BoINV2 lines also had a slower rate of floret sepal chlorosis after harvest compared with wild-type.     

Isolation and characterization of latherin, a surface-active protein from horse sweat.

A protein, latherin, with unusual surface activity was isolated from horse sweat by gel filtration and ion-exchange chromatography. The protein has a Stokes radius, determined by gel filtration, of 2.47 nm, and in the ultracentrifuge sediments as a single species with S20,W 2.05 S, indicating an Mr of 24,400. On SDS/polyacrylamide-gel electrophoresis the molecule behaves as a single peptide chain of apparent Mr 20,000. Latherin contains a high proportion of hydrophobic amino acids (37.2%), and the leucine content (24.5%) is exceptionally high. The unusual composition of the protein may account for apparent anomalies in the Mr of latherin determined by empirical methods. Evidence indicating that latherin is responsible for much of the surface activity of horse sweat was obtained by a simple assay for surface tension and by contact-angle measurements. Latherin adsorbs very readily at hydrophobic surfaces, rendering them wettable. A possible role for latherin in thermoregulation is proposed.     

The effect of visibility on territory size and shape

Although several authors have suggested that visibility affectsterritorial behavior, there have been few systematic studiesof this phenomenon. Here we review five ways that visibilitymight influence the use and defense of space in territorialanimals, and then we discuss a laboratory study on the effectof visibility on territory size and shape. Juvenile lizardswere allowed to establish territories in two habitats identicalexcept for a visual obstacle that bisected one of the two habitats.Lizards in the habitat with good visibility defended compactterritories of a size comparable to those in the field. In contrast,those in the low-visibility situation avoided territories thatincluded the visibility barrier and instead chose either verysmall or highly elongated territories. Territories with goodvisibility probably cost less to defend than those with poorvisibility; territory owners may also prefer high-visibilityterritories because they reduce predation risk or increase foragingsuccess.     

Interactions between plants: the role of mycorrhizae

Summary We present and discuss evidence, mostly from our own research, on some possible roles of mycorrhizae in interactions between plants. Experiments investigating whether seedlings become more rapidly infected with mycorrhiza if they are near large, already infected plants have shown that contact between the seedling's roots and established mycelium sometimes speeds up infection but on other occasions it does not. The reason for the discrepancies is not clear. Mycorrhiza can substantially alter the balance between competing plant species in a way that would not be predicted from their response when growing separately. An experiment involving large and small plants of the same species growing together showed little effect of mycorrhiza on the balance between plants of different sizes. The rate of transfer of ³²P between plants of Lolium perenne or Plantago lanceolata was so slow, even when they were mycorrhizal, that phosphorus transfer between living plants seems unlikely to be of major ecological importance. However, nitrogen was found to be transferred much more freely than phosphorus between P. lanceolata plants. Situations are discussed in which there could be a source-sink relationship between plants causing net flow of carbon or mineral nutrients from one to the other. If nutrients pass from dying roots to living plants via mycorrhizal links, this could result in preferential nutrient cycling between species that share the same type of mycorrhiza. Some evidence is presented that this does happen.     

Cell/substratum adhesions in RSV-transformed rat fibroblasts

Cell/substratum adhesions have been studied in rat fibroblasts transformed by a ts-mutant of Rous sarcoma virus (LA-29) using light and electron microscopy and a variety of preparative methods including immunolabeling. Cells were studied both during the process of transformation, i.e., shifting from 39 degrees to 35 degrees C, and in a fully transformed state (passaged at 35 degrees C continuously). The typical focal contacts observed at 39 degrees C (restrictive temperature) were replaced by "point-contacts" (100-200 per cell) which were classified by immunolabeling as podosome-like adhesions containing actin, beta 1 integrin subunit, vinculin, talin, alpha-actinin, and small membrane patches containing clathrin and integrin. Tyrosine-phosphorylated proteins and pp60src were found in association with groups of small particles on the protoplasmic surface of ventral membranes by gold immunolabeling. Both types of point-contacts were visualized by electron microscopy of ultrathin sections and shadowed replicas and characterized by gold immunolabeling wherever possible. The overall composition of podosome-like adhesions is similar to focal contacts but there are differences in the three-dimensional organization of the microfilaments and in the topography of vinculin which is associated more with actin filaments than with the plasma membrane. The presence of talin and extracellular matrix receptor in podosomes together with the adhesive properties of these actin-containing structures argues against the hypothesis that pp60src affects the interaction of actin with the plasma membrane by phosphorylating the fibronectin receptor and/or other associated proteins.