High frequency of phenotypic deviations in Physcomitrella patens plants transformed with a gene-disruption library.
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BACKGROUND: The moss Physcomitrella patens is an attractive model system for plant biology and functional genome analysis. It shares many biological features with higher plants but has the unique advantage of an efficient homologous recombination system for its nuclear DNA. This allows precise genetic manipulations and targeted knockouts to study gene function, an approach that due to the very low frequency of targeted recombination events is not routinely possible in any higher plant. RESULTS: As an important prerequisite for a large-scale gene/function correlation study in this plant, we are establishing a collection of Physcomitrella patens transformants with insertion mutations in most expressed genes. A low-redundancy moss cDNA library was mutagenised in E. coli using a derivative of the transposon Tn1000. The resulting gene-disruption library was then used to transform Physcomitrella. Homologous recombination of the mutagenised cDNA with genomic coding sequences is expected to target insertion events preferentially to expressed genes. An immediate phenotypic analysis of transformants is made possible by the predominance of the haploid gametophytic state in the life cycle of the moss. Among the first 16,203 transformants analysed so far, we observed 2636 plants (= 16.2%) that differed from the wild-type in a variety of developmental, morphological and physiological characteristics. CONCLUSIONS: The high proportion of phenotypic deviations and the wide range of abnormalities observed among the transformants suggests that mutagenesis by gene-disruption library transformation is a useful strategy to establish a highly diverse population of Physcomitrella patens mutants for functional genome analysis. (+info)
Influence of litter and weather on seedling recruitment in a mixed oak-pine woodland.
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The effects of regular litter removal and annual variation in temperature and precipitation on seedling recruitment of species differing in their seed size and mode of dispersal were studied in a 16-year (1984-1999) experiment in a mixed oak-pine wood in southern Poland. Litter was the most important factor in determining spatial variability in seedling recruitment, whereas differences in climatic conditions among years, especially temperature fluctuations in late winter and early spring, determined the temporal variability in seedling recruitment. Compared with control plots, significantly more new individuals of bryophytes and seedlings as well as a number of new species of vascular plants were noted in the litter-removal plots over the 16-year study. Litter strongly impeded seedling emergence of small-seeded species. The negative effect of litter on seedling recruitment of large-seeded species and the recruitment of new shoots in species growing clonally was much weaker. There was a significant positive correlation between the numbers of seedlings in the litter-removal and control plots and temperatures in January to March. In the litter-removal plots this mainly affected small-seeded species. Seedling recruitment was less consistently related to variation in precipitation. Positive relationships were found only between the number of seedlings of large-seeded species in the litter-removal plots and precipitation in July of the current year and in September of the previous year, and between the number of seedlings in the control plots and precipitation in September and November of the previous year. (+info)
Soil cations influence bryophyte susceptibility to bisulfite.
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The hypothesis that metal ions absorbed by bryophytes from the underlying soil may ameliorate adverse effects of SO2 was investigated in the terricolous moss species Pleurozium schreberi (Brid.) Mitt. and Rhytidiadelphus triquetrus (Hedw.) Warnst. Dilute sodium bisulfite solutions (equivalent to dissolved SO2) were applied to shoots isolated from soil or in contact with artificial substrata. Marked inhibition of net photosynthesis was observed within 2 h of treatment with 0.3 mM bisulfite in both mosses. Progressive recovery of net photosynthesis occurred 2-8 h after bisulfite treatment, although the extent of this depended on the concentration and pH of the solution. When R. triquetrus and P. schreberi were grown on artificial substrata (calcareous, acid-mineral or acid-organic) with weekly bisulfite applications, the only significant effect was poorer growth of P. schreberi receiving bisulfite on the calcareous and acid-organic substrata. In both species, growth on the calcareous substratum led to increased concentrations of exchangeable Ca2+, whereas exchangeable Fe3+ concentrations increased following growth on the acid-mineral soil. In another experiment the two mosses were pre-treated with either Ca2+ or Fe3+ before incubation with bisulfite. In P. schreberi, the depression of net photosynthetic rate caused by bisulfite was ameliorated from 33 to 64% of the control by pre-treatment with Fe3+, but it was unaffected by Ca2+ pre-treatment. In R. triquetrus, the amelioration caused by Fe3+ pre-treatment was from 16 to 60% of the control, but pre-treatment with Ca2+ gave a greater amelioration, to 75% of the control value. The responses are discussed in terms of soil preferences of the mosses and possible underlying bisulfite amelioration mechanisms. (+info)
Tip-growing cells of the moss Ceratodon purpureus Are gravitropic in high-density media.
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Gravity sensing in plants and algae is hypothesized to rely upon either the mass of the entire cell or that of sedimenting organelles (statoliths). Protonemata of the moss Ceratodon purpureus show upward gravitropism and contain amyloplasts that sediment. If moss sensing were whole-cell based, then media denser than the cell should prevent gravitropism or reverse its direction. Cells that were inverted or reoriented to the horizontal displayed distinct negative gravitropism in solutions of iodixanol with densities of 1.052 to 1.320 as well as in bovine serum albumin solutions with densities of 1.037 to 1.184 g cm(-3). Studies using tagged molecules of different sizes and calculations of diffusion times suggest that both types of media penetrate through the apical cell wall. Estimates of the density of the apical cell range from 1.004 to 1.085. Because protonemata grow upward when the cells have a density that is lower than the surrounding medium, gravitropic sensing probably utilizes an intracellular mass in moss protonemata. These data provide additional support for the idea that sedimenting amyloplasts function as statoliths in gravitropism. (+info)
Investigations on ecological effects of heavy metal pollution in Hungary by moss-dwelling water bears (Tardigrada), as bioindicators.
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The authors demonstrate a possible relationship between the concentrations of metals (Cd, Cr, Cu, Fe, Ni, Pb, V, Zn) measured in mosses and the composition of Tardigrade species detected in the same samples. Cushions of Hypnum cupressiforme were collected at 18 sites distributed in the whole of Hungary to estimate the background air pollution, then analyzed by ICP-AES to determine the concentrations of heavy metals. Data reflect the expected correlation; elevated heavy metal contents decrease the number of water bear species and of specimens, and abundance of Tardigrada depends strongly on air pollution. Higher concentrations of cadmium and chromium seem to have particularly damaging and toxic influence on community structure. As the biologically relevant effects of pollution can only be evaluated by carrying out measurements on the organisms themselves, our method applied species of Bryophyte and of Tardigrade, as bioindicators were appeared to be an adequate method to show the effect of air pollution on abundance of water bears. (+info)
Diverse plant and animal genetic records from Holocene and Pleistocene sediments.
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Genetic analyses of permafrost and temperate sediments reveal that plant and animal DNA may be preserved for long periods, even in the absence of obvious macrofossils. In Siberia, five permafrost cores ranging from 400,000 to 10,000 years old contained at least 19 different plant taxa, including the oldest authenticated ancient DNA sequences known, and megafaunal sequences including mammoth, bison, and horse. The genetic data record a number of dramatic changes in the taxonomic diversity and composition of Beringian vegetation and fauna. Temperate cave sediments in New Zealand also yielded DNA sequences of extinct biota, including two species of ratite moa, and 29 plant taxa characteristic of the prehuman environment. Therefore, many sedimentary deposits may contain unique, and widespread, genetic records of paleoenvironments. (+info)
Purification and characterization of a Ca(2+)-dependent/calmodulin-stimulated protein kinase from moss chloronema cells.
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We have demonstrated the presence of a Ca2+-dependent/calmodulin-stimulated protein kinase (PK) in chloronema cells of the moss Funaria hygrometrica. The kinase, with a molecular mass of 70,000 daltons (PK70), was purified to homogeneity using ammonium sulphate fractionation, DEAE-cellulose chromatography, and calmodulin (CaM)-agarose affinity chromatography. The kinase activity was stimulated at a concentration of 50 mM free Ca2+, and was further enhanced 3-5-fold with exogenously added 3-1000 nm moss calmodulin (CaM). Autophosphorylation was also stimulated with Ca2+ and CaM. Under in vitro conditions, PK70 phosphorylated preferentially lysine-rich substrates such as HIIIS and HVS. This PK shares epitopes with the maize Ca2+-dependent/calmodulin-stimulated PK (CCaMK) and also exhibits biochemical properties similar to the maize, lily, and tobacco CCaMK. We have characterized it as a moss CCaMK. (+info)
Effect of habitat fragmentation on levels and patterns of genetic diversity in natural populations of the peat moss Polytrichum commune.
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Peat bogs represent unique ecosystems that are under particular threat from fragmentation due to peat harvesting, with only 38% of the original peatland in Europe remaining intact and unaffected by peat cutting, drainage and silviculture. In this study, we have used microsatellite markers to determine levels and patterns of genetic diversity in both cut and uncut natural populations of the peat moss Polytrichum commune. Overall diversity levels suggest that there is more genetic variation present than had previously been assumed for bryophytes. Despite this, diversity values from completely cut bogs were found to be lower than those from uncut peatlands (average 0.729 versus 0.880). In addition, the genetic diversity was more highly structured in the cut populations, further suggesting that genetic drift is already affecting genetic diversity in peat bogs subjected to fragmentation. (+info)