Roots,nutrients and their relationship to spatial patterns

Ecosystem sustainability and resilience after a disturbance may be regulated by processes occurring at smaller spatial scales. The matrix of different spatial environments are created by (1) individual plants that accumulate higher concentrations of specific nutrients, trace elements or defensive plant secondary chemicals and thereby modify the chemistry of their ecological space and/or rates of processes, (2) the presence of structures (e.g., coarse woody debris) that may buffer some micro-environments from disturbances by functioning as a hospitable environment or as a reservoir for mycorrhizal fungi to sustain them into the next phase of stand development, and (3) chemical changes in soils during soil development which may result in distinct soil chemical environments. The response of the plants or change in the sustainability of carbon and nutrient cycles may be expressed more strongly at this smaller ecological space of an individual plant and furthermore must be frequently examined separately by the above- and belowground space of that individual.This paper will present three case studies from temperate and tropical forest ecosystems which suggest the importance of studying plant growth and nutrient and trace element cycling by stratifying sampling to encompass the mosaic patterns of existing spatial variability within the ecosystem. The examples show how individual plant species are able to create ecologically distinct spatial environments because of their distribution patterns within the landscape, how nutrient transfers in roots respond to the chemical variations in the soil, and how roots and mycorrhizal fungi are able to maintain themselves in the mosaic of coarse woody debris remaining on a site after the elimination of aboveground tree biomass.     

A new set of chemotaxis homologues is essential for Myxococcus xanthus social motility

Myxococcus xanthus cells aggregate and develop into multicellular fruiting bodies in response to starvation. A new M. xanthus locus, designated dif for defective in fruiting, was identified by the characterization of a mutant defective in fruiting body formation. Molecular cloning, DNA sequencing and sequence analysis indicate that the dif locus encodes a new set of chemotaxis homologues of the bacterial chemotaxis proteins MCPs (methyl-accepting chemotaxis proteins), CheW, CheY and CheA. The dif genes are distinct genetically and functionally from the previously identified M. xanthus frz chemotaxis genes, suggesting that multiple chemotaxis-like systems are required for the developmental process of M. xanthus fruiting body formation. Genetic analysis and phenotypical characterization indicate that the M. xanthus dif locus is required for social (S) motility. This is the first report of a M. xanthus chemotaxis-like signal transduction pathway that could regulate or co-ordinate the movement of M. xanthus cells to bring about S motility.     

Evolution of female mating preferences in stalk-eyed flies

Sensory exploitation predicts that female mate preferences existbefore the evolution of exaggerated male ornaments. We testedthis prediction by estimating female preference functions, rematingintervals, and copulation durations for three species of stalk-eyedflies. Two species, Cyrtodiopsis whitei and C dalmanni, exhibitextreme sexual dimorphism in eye span, with eye stalks exceedingbody length in large males. In contrast, C quinqucguttata ofboth sexes possess short eye stalks. Maximum parsimony analysisof 437 basepairs of the 16S mitochondrial ribosomal RNA genefrom 6 Malaysian diopsids reveals that short, sexually monomorphiceye stalks are plesiomorphic in Cyrtodiopsis. Observations ofmultiple copulations by females in paired-choice mating chambersindicated that female C whitei and C. dalmanni exhibit relativepreferences for longer eye stalks such that preference intensityincreases linearly with the difference in eye stalk length betweenmales. Females from the sexually monomorphic species showedno detectable preference for male eye stalk length. Female matingpreferences of bodi sexually dimorphic species exhibited significantrepeatability, as expected if genetic variation underlies thepreference. In addition, female C whitei and C. dalmanni exhibitedshorter copulations, mated more frequently, and rejected fewermating attempts than female C quinqueguttata. Thus, opportunitiesfor sperm competition have increased with acquisition of femalepreferences. We conclude that female sensory bias for maleswith long eye span did not exist in a common ancestor to thesespecies. Instead, female preference and remating propensityeither coevolved with eye span dimorphism or evolved after maleeye stalks elongated.     

Pollen advertisement: chemical contrasts between whole-flower and pollen odors

Odors of pollen and whole flowers were compared in taxonomically unrelated species that offer pollen as the only food reward to pollinators. Volatiles were collected using headspace adsorption and analyzed by gas chromatography and mass spectrometry. The odor of pollen was found to be chemically distinct from the total flower odor, and this pollen-odor distinctness varied among the three species. In Papaver rhoeas (Papaveraceae), the contrast between pollen and whole-flower odors was most subtle, with differences observed only in the proportions of individual volatiles (almost exclusively aliphatic hydrocarbons). In Filipendula vulgaris (Rosaceae), pollen volatiles were fewer than in the flowers (comprising mainly benzenoids and fatty-acid derivatives) and their relative proportions produced an odor dominated by 2-heptadecanone that contrasted strikingly with the flower odor dominated by 2-phenyl ethanol. In Lupinus polyphyllus (Fabaceae), the pollen odor contained fewer volatiles and in differing proportions than the flower fragrance (comprising almost exclusively isoprenoids). The findings add to earlier chemical evidence of odor contrasts between pollen and other flower parts in two other species. Drawing on information from pollination studies of these various species, it is suggested that pollen odor is used by pollen-foraging insects both to discriminate between plant species and to assess reward availability in individual flowers, and that it might in addition serve a protective function against destructive flower-feeding insects and pathogens.     

Molecular interactions between the photoreceptor G protein and rhodopsin

1. The visual transduction system of the vertebrate retina is a well-studied model for biochemical and molecular studies of signal transduction. The structure and function of rhodopsin, a prototypical G protein-coupled receptor, and transducin or Gt, the photoreceptor G protein, have been particularly well studied. Mechanisms of rhodopsin-Gt interaction are discussed in this review. 2. The visual pigment rhodopsin contains a chromophore, and thus conformational changes leading to activation can be monitored spectroscopically. A model of the conformational changes in the activated receptor is presented based on biophysical and biochemical data. 3. The current information on sites of interaction on receptors and cognate G proteins is summarized. Studies using synthetic peptides from amino acid sequences corresponding to Gt and rhodopsin have provided information on the sites of rhodopsin-Gt interaction. Synthetic peptides from the carboxyl terminal region of alpha t mimic Gt by stabilizing the active conformation of rhodopsin, Metarhodopsin II. 4. The conformation of one such peptide when it is bound to Metarhodopsin II was determined by 2D NMR. The model based on the NMR data was tested using peptide analogs predicted to stabilize or break the structure. These studies yield molecular insight into why toxin-treated and mutant G proteins are uncoupled from receptors.     

Identification of a highly conserved hydroxyproline-rich glycoprotein in the cell walls of Chlamydomonas reinhardtii and two other Volvocales

The unicellular alga Chlamydomonas reinhardtii Dang, has a cell wall made entirely from hydroxyproline-rich glycoproteins (HRGPs). We recently employed a quantiative in vitro reconstitution system (Adair et al. 1987, J. Cell Biol. 105, 2373–2382) to assign outer-wall HRGPs of C. reinhardtii to specific sublayers, and describe the major interactions responsible for their assembly. Some of these interactions appear to involve relatively conserved HRGP domains, as evidenced by interspecific cell-wall reconstitution between C. reinhardtii and two multicellular Volvocales (Volvoxcarteri lyengar and Gonium pectorale Müller). In the present report we provide biochemical and immunological evidence that the outer cell-walls of V. carteri and G. pectorale both contain prominent HRGPs closely related to C. reinhardtii GP2. Identification of conserved GP2 homologues indicates a molecular basis for interspecific reconstitution and provides a useful avenue for characterization of HRGP domains mediating cell-wall formation in these algae.Abbreviations GP1, 2, 3 outer-cell wall glycoproteins 1, 2, and 3 - GP2_dg deglycosylated GP2 - HRGP hydroxyprolinerich glycoprotein - SDS-PAGE sodium docecyl sulfate polyacrylamide gel electrophoresis     

Brominated Biphenyls Prime Extensive Microbial Reductive Dehalogenation of Aroclor 1260 in Housatonic River Sediment

The upper Housatonic River and Woods Pond (Lenox, Mass.), a shallow impoundment on the river, are contaminated with polychlorinated biphenyls (PCBs), the residue of partially dechlorinated Aroclor 1260. Certain PCB congeners have the ability to activate or “prime” anaerobic microorganisms in Woods Pond sediment to reductively dehalogenate the Aroclor 1260 residue. We proposed that brominated biphenyls might have the same effect and tested the priming activities of 14 mono-, di-, and tribrominated biphenyls (350 μM) in anaerobic microcosms of sediment from Woods Pond. All of the brominated biphenyls were completely dehalogenated to biphenyl, and 13 of them primed PCB dechlorination. Measured in terms of chlorine removal and decrease in the proportion of hexa- through nonachlorobiphenyls, the microbial PCB dechlorination primed by several brominated biphenyls was nearly twice as effective as that primed by chlorinated biphenyls. Congeners containing a meta bromine primed Dechlorination Process N (flanked meta dechlorination), and congeners containing an unflanked para bromine primed Dechlorination Process P (flanked para dechlorination). Two ortho-substituted congeners, 2-bromobiphenyl and 2,6-dibromobiphenyl (2-BB and 26-BB), also primed Process N dechlorination. The most effective primers were 26-BB, 245-BB, 25-3-BB, and 25-4-BB. The microbial dechlorination primed by 26-BB converted ~75% of the hexa- through nonachlorobiphenyls to tri- and tetrachlorobiphenyls in 100 days and removed ~75% of the PCBs that are most persistent in humans. These results represent a major step toward identifying an effective method for accelerating PCB dechlorination in situ. The challenge now is to identify naturally occurring compounds that are safe and effective primers.     

Growth,developmental and stress responses of larvae of the clouded sulphur butterfly Colias eriphyle to repeated exposure to high,sub‐lethal temperatures

The optimal temperature at which an organism grows and develops is commonly correlated with latitude and elevation; however, the maximum temperature for physiological performance often is not. This makes performance at temperatures between the optimum and the maximum of particular interest. Temperature can influence long‐term performance (growth and development), as well as short‐term performance (heat shock protein) responses differentially. In the present study, two populations of the clouded sulphur butterfly Colias eriphyle Edwards that differ in elevation, thermal regime and optimal and maximum temperatures are studied to quantify their responses to repeated, sub‐lethal heat treatments early in development (second instar). Heat treatments accelerate development during the second to fourth instars in both populations initially, although this effect disappears by pupation. Heat treatment decreases pupal mass in the lower elevation population, suggesting that repeated exposure to high temperatures early in development may reduce final size and fecundity in this population. Heat shock protein gene (hsp70) expression levels in the lower elevation (1633 m a.s.l.) population are highest 24 h after the start of the heat treatment and then the fall to pre‐exposure levels by 36–72 h, suggesting a rapid response to stressful temperatures. By contrast, heat treatment has no significant effect on pupal mass in the higher elevation (2347 m a.s.l.) population. This population has higher levels of hsp70 expression overall but constant expression levels, suggesting that the temperature treatments used are insufficient to elicit a heat stress response. Overall, the effects of repeated exposure to sub‐lethal high temperatures early in development on growth, final size and gene expression differ between populations that differ in thermal sensitivity.     

Pneumolysin-damaged cells benefit from non-homogeneous toxin binding to cholesterol-rich membrane domains

Nucleated cells eliminate lesions induced by bacterial pore-forming toxins, such as pneumolysin via shedding patches of damaged plasmalemma into the extracellular milieu. Recently, we have shown that the majority of shed pneumolysin is present in the form of inactive pre-pores. This finding is surprising considering that shedding is triggered by Ca²⁺-influx following membrane perforation and therefore is expected to positively discriminate for active pores versus inactive pre-pores.Here we provide evidence for the existence of plasmalemmal domains that are able to attract pneumolysin at high local concentrations. Within such a domain an immediate plasmalemmal perforation induced by a small number of pneumolysin pores would be capable of triggering the elimination of a large number of not yet active pre-pores/monomers and thus pre-empt more frequent and perilous perforation events. Our findings provide further insights into the functioning of the cellular repair machinery which benefits from an inhomogeneous plasmalemmal distribution of pneumolysin.