Colonisation of spruce roots by two interacting ectomycorrhizal fungi in wood ash amended substrates

Interactions between two ectomycorrhizal fungal species, Piloderma croceum Erikss. and Hjortst. and Piloderma sp. 1 (found to colonise spruce roots and wood ash granules in the field), were investigated in wood ash amended substrates. The comparative ability of these fungi to colonise roots of non-mycorrhizal spruce (Picea abies (L.) Karst.) seedlings was studied in relation to factorial combinations of wood ash and N fertilisation. Non-mycorrhizal spruce seedlings (bait seedlings) were planted together with spruce seedlings colonised by P. croceum or Piloderma sp. 1. The growth substrate was a sand-peat mixture with wood ash or no ash and supplied with two levels of N, so that four substrate combinations were obtained. Piloderma sp. 1 mycelia colonised around 60% of the fine roots of bait seedlings in ash treatments regardless of N level and around 20-26% in treatments without ash. P. croceum only colonised 8% of the root tips in the presence of ash but 56% of the root tips in the low-N treatment without ash. However, in the high-N treatment without ash the colonisation level was reduced to around 30%. Total numbers of root tips per seedling did not vary significantly between the treatments. Possible reasons for the competitive advantage of Piloderma sp. 1 in wood ash fertilised substrate are discussed.     

Early research on the role of plastocyanin in photosynthesis

A review is presented of the early history of investigations into the function of the blue copper-protein plastocyanin in photosynthesis. The controversy or confusion that arose as to the function of plastoycanin in conjunction with cytochrome f and cytochrome c ₆ is discussed and investigations contributing to the establishment of the role of plastocyanin as the mobile electron carrier between the Photosystem I reaction center complex and the cytochrome b ₆/f complex are described. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tryptophanyl fluorescence lifetime distribution of hyperthermophilic beta-glycosidase from molecular dynamics simulation: a comparison with the experimental data

A molecular dynamics simulation approach has been utilized to understand the unusual fluorescence emission decay observed for beta-glycosidase from the hyperthermophilic bacterium Solfolobus sulfotaricus (Sbeta gly), a tetrameric enzyme containing 17 tryptophanyl residues for each subunit. The tryptophanyl emission decay of Sbeta gly results from a bimodal distribution of fluorescence lifetimes with a short-lived component centered at 2.5 ns and a long-lived one at 7.4 ns (Bismuto E, Nucci R, Rossi M, Irace G, 1999, Proteins 27:71-79). From the examination of the trajectories of the side chains capable of causing intramolecular quenching for each tryptophan microenvironment and using a modified Stern-Volmer model for the emission quenching processes, we calculated the fluorescence lifetime for each tryptophanyl residue of Sbeta gly at two different temperatures, i.e., 300 and 365 K. The highest temperature was chosen because in this condition Sbeta gly evidences a maximum in its catalytic activity and is stable for a very long time. The calculated lifetime distributions overlap those experimentally determined. Moreover, the majority of trytptophanyl residues having longer lifetimes correspond to those originally identified by inspection of the crystallographic structure. The tryptophanyl lifetimes appear to be a complex function of several variables, such as microenvironment viscosity, solvent accessibility, the chemical structure of quencher side chains, and side-chain dynamics. The lifetime calculation by MD simulation can be used to validate a predicted structure by comparing the theoretical data with the experimental fluorescence decay results.     

Flatworm phylogeny from partial 18S rDNA sequences

Partial 18S rDNA sequences from 29 flatworms and 2 outgroup taxa were used in a cladistic analysis of the Platyhelminthes. Support for the clades in the resulting single most parsimonious tree was estimated through bootstrap analysis, jack-knife analysis and decay indices. The Acoelomorpha (Acoela and Nemertodermatida) were absent from the most parsimonious tree. The Acoela and the Fecampiidae form a strongly supported clade, the sister group of which may be the Tricladida. There is some support for monophyly of the rhabdocoel taxon Dalyellioida, previously regarded as paraphyletic. The sister group of the Neodermata remains unresolved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Perspectives in the glycosciences – matrix-assisted laser desorption/ionization (MALDI) mass spectrometry of carbohydrates

The technique of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is reviewed with emphasis on the best type of matrix to use with carbohydrates, ways to obtain fragmentation and use of the technique for carbohydrate sequencing. © 1998 Rapid Science Ltd     

Acetic Acid, Ethanol and Steam Effects on the Growth of Botrytis cinerea in vitro and Combination of Steam and Modified Atmosphere Packaging to Control Decay in Kiwifruit

The effects of acetic acid fumigation, ethanol fumigation, and steam heat treatment on growth of Botrytis cinerea in vitro were investigated. The effect of steam heat treatments in combination with modified atmosphere packaging (MAP) on Botrytis decay development on 'Hayward' kiwifruit was also studied. The fungus was grown in Petri dishes on potato dextrose agar. Ethanol fumigation with 100  μ l/l for 3 or 6 min, or 200  μ l/l for 6 min enhanced the growth of B. cinerea . The effect of acetic acid on growth of B. cinerea was time and dosage-dependent. Fumigation with 1  μ l/l for 6 min, 2  μ l/l for 3 min, and 4  μ l/l for 3 min promoted radial growth of the fungus when compared to the growth of the untreated control. Fumigation with 2  μ l/l for 6 min delayed the growth of the fungus for the first 6 days, while fumigation with 6  μ l/l for 3 min delayed the growth of the fungus after the sixth day. Fumigation with 4 or 6  μ l/l acetic acid for 6 min, and 8  μ l/l acetic acid for 3 or 6 min resulted in complete inhibition of fungal growth. Steam heat treatment at 45°C for 6 min, and at 48, 51, and 54°C for 3 or 6 min completely inhibited fungal growth in vitro . Furthermore, steam treatments at 47, 50, and 53°C for 3 or 6 min completely inhibited decay at the stem end of kiwifruit kept at 10°C in MAP for 12 days. However, none of the steam treatments inhibited decay in wounds on the surface of the fruit kept in MAP.     

Long-term patterns of mass loss during the decomposition of leaf and fine root litter: an intersite comparison

Decomposition is a critical process in global carbon cycling. During decomposition, leaf and fine root litter may undergo a later, relatively slow phase; past long-term experiments indicate this phase occurs, but whether it is a general phenomenon has not been examined. Data from Long-term Intersite Decomposition Experiment Team, representing 27 sites and nine litter types (for a total of 234 cases) was used to test the frequency of this later, slow phase of decomposition. Litter mass remaining after up to 10 years of decomposition was fit to models that included (dual exponential and asymptotic) or excluded (single exponential) a slow phase. The resultant regression equations were evaluated for goodness of fit as well as biological realism. Regression analysis indicated that while the dual exponential and asymptotic models statistically and biologically fit more of the litter type–site combinations than the single exponential model, the latter was biologically reasonable for 27–65% of the cases depending on the test used. This implies that a slow phase is common, but not universal. Moreover, estimates of the decomposition rate of the slowly decomposing component averaged 0.139–0.221 year⁻¹ (depending on method), higher than generally observed for mineral soil organic matter, but one-third of the faster phase of litter decomposition. Thus, this material may be slower than the earlier phases of litter decomposition, but not as slow as mineral soil organic matter. Comparison of the long-term integrated decomposition rate (which included all phases of decomposition) to that for the first year of decomposition indicated the former was on average 75% that of the latter, consistent with the presence of a slow phase of decomposition. These results indicate that the global store of litter estimated using short-term decomposition rates would be underestimated by at least one-third.     

氟对镍钛拉簧的腐蚀性研究

目的:研究模拟应用氟化物防龋的口腔环境下,不同浓度氟化物对镍钛拉簧的应力衰减的影响。方法:选取两种国内常用品牌0.010 inch镍钛拉簧各40根,随机将每种拉簧平均分入四个浓度组(0.05%、0.10%、0.15%和对照组),将相同浓度组的不同品牌弹簧分别固定于间距为20 mm的四个支架的两端。将四个支架分别放入37℃人工唾液中水浴。将实验组按浓度分组放入不同浓度氟化人工唾液(0.05%、0.10%、0.15%)中处理5 min,每天三次。分别于实验前、实验后1周、2周、3周、4周用拉伸机测量每根弹簧拉伸至20 mm时的应力。对实验结果使用重复测量的方差分析。结果:时间因素对两种镍钛拉簧拉伸应力的衰减的影响有统计学意义,氟化物浓度有辅助效应,二者有交互作用。氟化物作用下不同品牌镍钛拉簧的应力腐蚀变化不同。(P0.05)。结论:1.氟化物的存在可以增加镍钛拉簧的应力衰减。2.在正畸治疗的临床工作中在使用氟化物时应考虑增加镍钛拉簧的更换频率。