Effect of C4 Depletion on the Utilization of the Terminal Components of Guinea-pig Complement by Endotoxin

ENDOTOXIN and antigen-antibody complexes (Ag-Ab) are potent inflammatory agents which induce marked pathophysiological effects in a number of animal species. Both these agents lead to increased vascular permeability, local accumulations of polymorphonuclear leucocytes and alterations in the coagulability of blood¹. There is mounting evidence that these similarities derive from endotoxins and Ag-Ab being activators of the complement (C) system, an important mediator of inflammation¹'². When endotoxins or preformed Ag-Ab are reacted with normal guinea-pig (GP) serum so as to induce equivalent consumption of whole haemolytic C, there are, however, striking differences in the consumption profiles of the individual C components³. Although interaction of Ag-Ab with GP serum results in the consumption of CI, C4 and C2 as well as C3 to C9, the interaction of endotoxin with GP serum leads to a marked depletion of C3 to C9 with little or no detectable loss of C1,C4 and C2 (ref. 3).     

Global change and biological soil crusts: effects of ultraviolet augmentation under altered precipitation regimes and nitrogen additions

Biological soil crusts (BSCs), a consortium of cyanobacteria, lichens, and mosses, are essential in most dryland ecosystems. As these organisms are relatively immobile and occur on the soil surface, they are exposed to high levels of ultraviolet (UV) radiation and atmospheric nitrogen (N) deposition, rising temperatures, and alterations in precipitation patterns. In this study, we applied treatments to three types of BSCs (early, medium, and late successional) over three time periods (spring, summer, and spring–fall). In the first year, we augmented UV and altered precipitation patterns, and in the second year, we augmented UV and N. In the first year, with average air temperatures, we saw little response to our treatments except quantum yield, which was reduced in dark BSCs during one of three sample times and in Collema BSCs two of three sample times. There was more response to UV augmentation the second year when air temperatures were above average. Declines were seen in 21% of the measured variables, including quantum yield, chlorophyll a, UV‐protective pigments, nitrogenase activity, and extracellular polysaccharides. N additions had some negative effects on light and dark BSCs, including the reduction of quantum yield, β‐carotene, nitrogenase activity, scytonemin, and xanthophylls. N addition had no effects on the Collema BSCs. When N was added to samples that had received augmented UV, there were only limited effects relative to samples that received UV without N. These results indicate that the negative effect of UV and altered precipitation on BSCs will be heightened as global temperatures increase, and that as their ability to produce UV‐protective pigments is compromised, physiological functioning will be impaired. N deposition will only ameliorate UV impacts in a limited number of cases. Overall, increases in UV will likely lead to lowered productivity and increased mortality in BSCs through time, which, in turn, will reduce their ability to contribute to the stability and fertility of soils in dryland regions.     

Chromosome numbers and karyotypes of South American species and populations of Hypochaeris (Asteraceae)

One hundred and thirty-seven new chromosome counts are reported from 104 populations of 26 native South American taxa of Hypochaeris (Asteraceae, Lactuceae), together with two invasive Mediterranean species: H. glabra and H. radicata . First reports are provided for seven taxa ( H. alba , H. cf. eremophila , H. caespitosa , H. hookeri , H. parodii , H. patagonica and H. pinnatifida ) and one new ploidy level is reported (diploid for H. incana , so far known only as a tetraploid). Including the results of this study, the chromosomes of 39 of the c . 50 Hypochaeris species known from the New World have now been counted. Most species are diploid with 2 n  = 2 x  = 8 and have bimodal, asymmetrical karyotypes. Tetraploidy (2 n  = 4 x  = 16) is reported here for the first time in H. caespitosa . Infra-specific polyploidy (probably autopolyploidy) is reported in H. incana and H. taraxacoides , both cases including infra-populational cytotype mixtures (2 x and 4 x ). Polyploidy is now known from eight South American Hypochaeris species ( c . 16%). Basic karyotype analyses allow the placement of the newly counted taxa into previously proposed but slightly modified groupings and provide the framework for further molecular cytogenetic analyses. The reported findings suggest that chromosomal change in South American Hypochaeris , in contrast to Old World species, has not involved aneuploidy, but polyploidy and/or more subtle changes in chromosome length, perhaps via satellite DNA amplification/deletion or activity of retroelements, and rDNA reorganization.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 49–60.     

[CO2]- and density-dependent competition between grassland species

The predicted ongoing increase of atmospheric carbon dioxide levels is considered to be one of the main threats to biodiversity due to potential changes in biotic interactions. We tested whether effects of intra‐ and interspecific planting density of the calcareous grassland perennials Bromus erectus and Carex flacca change in response to elevated [CO₂] (600 ppm) by using factorial combinations of seven densities (0, 1, 2, 4, 8, 16, 24 tillers per 8 × 8 cm² cell) of both species in plots with and without CO₂ enrichment. Although aboveground biomass of C. flacca was increased by 54% under elevated [CO₂], the combined aboveground biomass of the whole stand was not significantly increased. C. flacca tended to produce more tillers under elevated [CO₂] while B. erectus produced less tillers. The positive effect of [CO₂] on the number of tillers of C. flacca was strongest at high intraspecific densities. On the other hand, the negative effect of [CO₂] on the number of tillers of B. erectus was not present at intermediate intraspecific planting densities. Seed production of C. flacca was more than doubled under elevated [CO₂], while seed production of B. erectus was not affected. Moreover, the mass per seed of C. flacca was increased by elevated [CO₂] at intermediate interspecific planting densities while the mass per seed of B. erectus was decreased by elevated [CO₂] at high interspecific planting densities. Our results show that the responses of C. flacca and B. erectus to elevated [CO₂] depend in a complex way on initial planting densities of both species. In other words, competition between these two model species is both [CO₂]‐ and density dependent. On average, however, the effects of [CO₂] on the individual species indicate that the composition of calcareous grasslands is likely to change under elevated [CO₂] in favor of C. flacca.     

Analysis of cytosolic and plastidic serine acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for cysteine biosynthesis in Arabidopsis

In plants, the enzymes for cysteine synthesis serine acetyltransferase (SAT) and O-acetylserine-(thiol)-lyase (OASTL) are present in the cytosol, plastids and mitochondria. However, it is still not clearly resolved to what extent the different compartments are involved in cysteine biosynthesis and how compartmentation influences the regulation of this biosynthetic pathway. To address these questions, we analysed Arabidopsis thaliana T-DNA insertion mutants for cytosolic and plastidic SAT isoforms. In addition, the subcellular distribution of enzyme activities and metabolite concentrations implicated in cysteine and glutathione biosynthesis were revealed by non-aqueous fractionation (NAF). We demonstrate that cytosolic SERAT1.1 and plastidic SERAT2.1 do not contribute to cysteine biosynthesis to a major extent, but may function to overcome transport limitations of O-acetylserine (OAS) from mitochondria. Substantiated by predominantly cytosolic cysteine pools, considerable amounts of sulphide and presence of OAS in the cytosol, our results suggest that the cytosol is the principal site for cysteine biosynthesis. Subcellular metabolite analysis further indicated efficient transport of cysteine, γ -glutamylcysteine and glutathione between the compartments. With respect to regulation of cysteine biosynthesis, estimation of subcellular OAS and sulphide concentrations established that OAS is limiting for cysteine biosynthesis and that SAT is mainly present bound in the cysteine–synthase complex.     

Ontogeny of the mycoheterotrophic species Afrothismia hydra (Burmanniaceae)

The complete ontogeny of the mycoheterotrophic Afrothismia hydra (Burmanniaceae) from seed to seed dispersal is presented. The oblong–ovoidal seeds are up to 0.7 mm long. They germinate with root tissue only, disrupting the seed coat and developing a primary ovoid root tubercle. At the proximal end of the tubercle, a second tubercle arises and further root initials indicate the sequential growth of more root tubercles with filiform extensions resulting in a small root aggregate. The seed coat often remains attached to this structure. When the root aggregate enlarges, a central axis to which all roots are connected becomes visible. This axis has a growth pole where new root tubercles arise. The same growth pole will later develop into a stem with scale leaves finally terminating in a flower. Flowers develop sympodially when the mature plant is only several centimetres long. After anthesis, the corolla tube disintegrates, leaving a pyxidium which opens by means of a peculiar elongating placenta, here called 'placentophore'. The placentophore elevates the placenta with attached seeds above the flowering level and is interpreted as an adaptation to ombrohydrochory. The reduction of hypocotyl, cotyledon and primary shoot is discussed with regard to the classical germination concepts of monocotyledons and with mycoheterotrophic dicotyledons.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 31–36.     

Conifer stem growth at the altitudinal treeline in response to four years of CO2 enrichment

Northern latitude and upper altitude climatic treelines have received increasing attention given their potential sensitivity to atmospheric and climate change. While greater radial stem growth at treeline sites in recent decades has been attributed largely to increasing temperature, rising atmospheric CO₂ concentration may also be contributing to this growth stimulation. Tree ring increments of mature Larix decidua and Pinus uncinata were measured over 4 years in a free air CO₂ enrichment experiment at treeline in the Swiss Central Alps (2180 m a.s.l.). In addition, a one‐time defoliation treatment in the second year (2002) of the experiment was used to simulate one of the common natural insect outbreak events. In response to elevated atmospheric CO₂, Larix showed a cumulative 4‐year growth response of+41%, with particularly strong responses in the third and fourth year. This increase in radial stem wood growth was the result of more latewood production, in particular, the formation of larger tracheids, rather than a greater number of cells. In contrast, Pinus showed no change in ring width to elevated [CO₂], neither in each of the treatment years, nor in the cumulative response over 4 years, although an increase in tracheid size was observed in the third year. Defoliation led to a pronounced decrease in annual ring width of both species, marked in particular by less latewood production, in the treatment, as well as subsequent years. There was no significant interaction between defoliation and CO₂ enrichment. Although Pinus showed no growth response to CO₂, the positive growth response observed in Larix after 4 years of CO₂ enrichment implies that the sensitivity of treeline trees to global change may not be purely temperature driven. We conclude that the open sparse canopy in the treeline ecotone favours the indeterminate growth strategy of the early successional Larix when neither weather nor carbon are limiting, whereas the later successional Pinus does not show any indication of more vigorous growth under future higher atmospheric CO₂ concentrations.