Aroma biosynthesis in strawberry: s-adenosylmethionine:furaneol o-methyltransferase activity in ripening fruits

Among the most important volatile compounds in the aroma of strawberries are 2,5-dimethyl-4-hydroxy-3(2H)-furanone (Furaneol) and its methoxy derivative (methoxyfuraneol, mesifuran). Three strawberry varieties, Malach, Tamar, and Yael, were assessed for total volatiles, Furaneol, and methoxyfuraneol. The content of these compounds sharply increased during fruit ripening, with maximum values at the ripe stage. An enzymatic activity that transfers a methyl group from S-adenosylmethionine (SAM) to Furaneol sharply increases during ripening of strawberry fruits. The in vitro generated methoxyfuraneol was identified by radio-TLC and GC-MS. The partially purified enzyme had a native molecular mass of approximately 80 kDa, with optimum activity at pH 8.5 and 37 degrees C. A high apparent K(m) of 5 mM was calculated for Furaneol, whereas this enzyme preparation apparently accepted as substrates other o-dihydroxyphenol derivatives (such as catechol, caffeic acid, and protocatechuic aldehyde) with much higher affinities (K(m) approximately 105, 130, and 20 microM, respectively). A K(m) for SAM was found to be approximately 5 microM, regardless of the acceptor used. Substrates that contained a phenolic group with only one OH group, such as p-coumaric and trans-ferulic acid, as well as trans-anol and coniferyl alcohol, were apparently not accepted by this activity. It is suggested that Furaneol methylation is mediated by an O-methyltransferase activity and that this activity increases during fruit ripening.     

Intellectual Property: Information Ownership in the Electronic Age: The Government Perspective: Government's Role in Striking a Balance in the Public Interest

ABSTRACT

An overview of the National Agricultural Library's eleven specialized information centers is presented that includes information on electronic access to their databases, publications, and information.     

Soil and microbial C:N:P stoichiometries play vital roles in regulating P transformation in agricultural ecosystems: A review

Stoichiometry plays a crucial role in biogeochemical cycles and can modulate soil nutrient availability and functions. In agricultural ecosystems,phosphorus(P) fertilizers(organic or chemical) are often applied to achieve high crop yields. However, P is readily fixed by soil particles, leading to low P use efficiency. Therefore, understanding the role of carbon:nitrogen:P stoichiometries of soil and microorganisms in soil P transformation is of great significance for P management in agriculture....     

2︰1和1︰1型黏土矿物胶体凝聚中Hofmeister效应的比较研究

土壤胶体是土壤具备肥力与生态功能的物质基础,土壤胶体凝聚与分散影响着土壤中一系列微观过程和宏观现象。采用动态光散射技术比较研究三种碱金属阳离子(Li+、Na+、K+)引发不同类型黏土矿物(2︰1型蒙脱石和1︰1型高岭石)胶体凝聚中的Hofmeister效应。研究发现,Li+、Na+、K+作用下蒙脱石、高岭石胶体的凝聚速率、临界聚沉浓度及活化能都存在明显差异,表现出强烈的Hofmeister效应。当电解质浓度为20 mmol·L–1时,K+引发蒙脱石胶体凝聚的速率为66.61 nm·min–1,远高于Na+、Li+引发蒙脱石胶体凝聚速率(5.93、4.41 nm·min–1);而与之对应的临界聚沉浓度则呈现K+(蒙脱石21.8 mmol·L–1、高岭石34.6 mmol·L–1)低于Na+(蒙脱石57.6 mmol·L–1、高岭石85.8 mmol·L–1)低于Li+(蒙脱石81.8 mmol·L–1、高岭石113.9 mmol·L–1)规律,胶体凝聚中活化能可合理解释此现象。电解质浓度为25 mmol·L–1时,Li+、Na+、K+引发蒙脱石、高岭石胶体凝聚的活化能分别为1.97 kT、1.43 kT、0 kT和2.94 kT、1.71 kT、0.49 kT,说明蒙脱石、高岭石胶体凝聚过程中Hofmeister效应序列均为Li+相似文献   

Denitrification in soil: Effects of herbicides

The effects of 20 herbicides on denitrification of nitrate in three soils were studied by determining the effects of 10 and 50μgg^?1 soil of each herbicide on the amounts of nitrate lost and the amounts of nitrite, N₂O and N₂ produced when soil samples were incubated anaerobically after treatment with nitrate. The herbicides used were butylate, EPTC, chlorpropham, propham, diuron, linuron, monuron, siduron, alachlor, trifluralin, 2,4-D amine, 2,4-D ester, atrazine, cyanazine, metribuzin, simazine, dalapon, chloramben, dicamba and dinoseb.None of the herbicides studied significantly affected denitrification of nitrate when applied at the rate of 10 μg g^?1 soil, but dinoseb increased the ratio of N₂ to N₂O in the gaseous products of denitrification when applied at this rate. Butylate, EPTC, diuron, simazine and dalapon had no significant effect on denitrification when applied at the rate of 50μgg^?1 soil, whereas metribuzin and dinoseb enhanced denitrification when applied at this rate. The influence of the other herbicides on denitrification when applied at the rate of 50μgg^?1soil depended on the soil, but all enhanced or inhibited denitrification in at least one soil.     

湿地土壤氮素研究概述

湿地是自然界最富生物多样性的生态景观和人类最重要的生存环境之一,具有巨大的环境调节功能和效益。湿地发挥着N素的源、汇和转换器的功能,而湿地土壤中N素含量及其迁移转化过程也显著影响着湿地生态系统的结构和功能,所以湿地土壤N素过程研究成为当前研究热点之一。本文对湿地土壤N素贮量,湿地对N素的截留能力以及湿地N素的迁移转化过程等方面进行了综述。     

Lead in urban dust: An assessment

Sufficient evidence has accumulated during the past decade to suggest that environmental Pb may be responsible for a deterioration in the mental and behavioral performance of some children. A knowledge of the pathways by which environmental Pb reaches the body is therefore important in the assessment and control of environmental Pb pollution. These pathways are discussed and it is argued that Pb in dust is one of the more useful indices of contamination of the environment by Pb. Those studies from which a quantitative relationship between blood-Pb level and Pb-in-dust concentration can be inferred are listed, and some theoretical consideration of the relationship is given. In conclusion, a Pb-in-dust concentration which; if exceeded on a widespread scale in residential areas, demands some action by the controlling authority is suggested.     

Aminochelates in plant nutrition: a review

Chelates are compounds that are applied to improve nutrition, especially the micronutrients status of plant tissues. During past decades, various chelating agents have been synthesized and introduced to agricultural systems. The recent formulas are aminochelates that are synthesized using various amino acids and a single or several nutrient ions aimed at improving fertilizer use efficiency and more adaptation to environment protection. Apart from their primary use as a micronutrient source, aminochelates represent an effective nitrogen (N) fertilizer in plant nutrition that can avoid negative effects from simple N fertilizers, such as urea. In various studies, higher yield and quality as well as higher concentration of nutrient elements have been obtained by application of aminochelates rather than simple chemical fertilizers. These compounds claimed to be more natural and safer forms of chelating agents, with higher use efficiency and without environmental side effects. However, there is lack of sufficient knowledge especially regarding their detailed impacts and their fate within the soil and plant system. This review provides information concerning the role of aminochelates in plant nutrition and to summarize the previous recent studies that have been done using these fertilizers.     

Nature conservation in rhodesia: A review

The history of conservation is outlined and the present status and aims are reviewed. There are six types of conservation area in Rhodesia which are listed and described in terms of their present location, size, floristic and faunistic components, planning stage, conservation and management status. Management problems are defined and the ongoing research programme is tabulated. The need for a reappraisal of practical management and planning principles are discussed using a case history as an example.     

Proteolytic activity in soil: A review

The aim of this work is to review current knowledge on inputs, sources and regulation of protease activities in soils from different ecosystems, while exploring limitations to proteolysis and N mineralisation. Extracellular proteases enter the soil via microbial production and other sources, including plant root exudates, animal excrements, decomposition processes and leaching from agro-industrial fertilisers. The synthesis and activities of proteases in soil are regulated by many factors, including climate, soil properties and the presence of organic compounds of plant and microbial origin. Two particularly important areas for future research are the regulation of proteolysis by low-molecular-weight organic compounds, including amino acids, sugars, flavonoids, plant hormones and siderophores, as well as the identification and characterisation of proteinaceous protease inhibitors of plant and microbial origin in the soil. Despite all the work that has been performed on soil proteases, our understanding of the roles of extracellular plant root proteases in N nutrition is weak. Furthermore, the regulation of soil proteolytic activities of different ecosystems, especially in terms of pollutant inputs and the impact of climate change, requires investigation. Other areas that pose important questions for the future include assessments of protease inhibitor inputs to the soil, regulation of these inhibitors via naturally occurring soil organic compounds and the interactions between soil organisms.     

Phytoremediation Technology: Hyper-accumulation Metals in Plants

This paper reviews key aspects of phytoremediation technology and the biological mechanisms underlying phytoremediation. Current knowledge regarding the application of phytoremediation in alleviating heavy metal toxicity is summarized highlighting the relative merits of different options. The results reveal a cutting edge application of emerging strategies and technologies to problems of heavy metals in soil. Progress in phytoremediation is hindered by a lack of understanding of complex interactions in the rhizosphere and plant based interactions which allow metal translocation and accumulation in plants. The evolution of physiological and molecular mechanisms of phytoremediation, together with recently-developed biological and engineering strategies, has helped to improve the performance of both heavy metal phytoextraction and phytostabilization. The results reveal that phytoremediation includes a variety of remediation techniques which include many treatment strategies leading to contaminant degradation, removal (through accumulation or dissipation), or immobilization. For each of these processes, we review what is known for metal pollutants, gaps in knowledge, and the practical implications for phytoremediation strategies.     

Synthesis: Thresholds in conservation and management

This paper is a brief overview of some of the key issues which have emerged from the preceding set of papers on ecological thresholds. These include:

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Whether threshold relationships are common and widespread.

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The potential for large variations in the use and application of the threshold concept to lead to adverse conservation outcomes, particularly when overly simplistic levels of vegetation cover are specified by policy makers and land managers.

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The inherent multi-variate nature of landscape processes and responses of individual species and assemblages that creates variability in datasets. This may lead to a limited ability to make accurate predictions from threshold relationships, even when those relationships are highly statistically significant.

We believe that although the threshold concept is an appealing one and there is some empirical evidence to support it in some landscapes, it is not free of problems and a concerted research effort on the topic is needed. This is particularly important if it is to have value for robustly underpinning applied landscape management practices without unintentionally having negative impacts on rates of species loss or the loss of particular species.     

Surface-water gley soils in Bangladesh: Genesis

Extensive areas of periodically wet, acid soils in Bangladesh have a seasonally fluctuating pH of the surface horizon and evidence for net clay loss. Morphological, chemical, mineralogical and other data mainly on a typical profile of these surface-water gley soils indicate a clay loss of some 1.5 kg/dm' ; alteration of smectite to a soil chlorite, interlayered material with trapped ferrous iron; the consequent drop in C.E.C. of the clay fraction; and the presence of amorphous silica. The data were used to reconstruct a sequence of three soil forming processes: Vertisol formation, then argilluviation, followed by ferrolysis.Ferrolysis involves, in the wet season: reduction producing ferrous iron, which displaces part of the exchangeable basic cations and aluminium; leaching of bases and part of the aluminium; and interlayer formation by the remaining aluminium while some exchangeable ferrous iron is trapped in the interlayers. In the dry season, oxidation of exchangeable ferrous iron produces exchangeable hydrogen, part of which attacks the clay minerals and is neutralized by liberation of Al, Mg and other ions from the clay structure. Part of the silica remaining from the clay structure is leached out in the next wet season, part accumulates in amorphous form. In soils long used for paddy cultivation, man has concentrated the ferrolysis process in the ploughed layer by the formation of a slowly permeable ploughpan causing strong reduction only in the surface horizon.The hydromorphic albic horizon over more clayey material is indicative of the dominant process in surface-water gley soils. This sequum could usefully have a more important place in soil classification than it has at present, e.g. at great group level.