Biophilia: does visual contact with nature impact on health and well-being?

It is concluded that an environment devoid of Nature may act as a “discord”, i.e., have a negative effect. While the term mismatch is used for any difference between present living conditions and the environment of evolutionary adaptation, discords are mismatches with a potentially undesirable impact on health or quality of life. The problem is partly due to the visual absence of plants, and may be ameliorated by adding elements of Nature, e.g., by creating parks, by offering a view through windows, and by potted plants. The conclusion is based on an evaluation of some fifty relevant empirical studies.

Regulation by salt of vacuolar H+-ATPase and H+-pyrophosphatase activities and Na+/H+ exchange

Over the last decades several efforts have been carried out to determine the mechanisms of salt homeostasis in plants and, more recently, to identify genes implicated in salt tolerance, with some plants being successfully genetically engineered to improve resistance to salt. It is well established that the efficient exclusion of Na(+) excess from the cytoplasm and vacuolar Na(+) accumulation are the most important steps towards the maintenance of ion homeostasis inside the cell. Therefore, the vacuole of plant cells plays a pivotal role in the storage of salt. After the identification of the vacuolar Na(+)/H(+) antiporter Nhx1 in Saccharomyces cerevisiae, the first plant Na(+)/H(+) antiporter, AtNHX1, was isolated from Arabidopsis and its overexpression resulted in plants exhibiting increased salt tolerance. Also, the identification of the plasma membrane Na(+)/H(+) exchanger SOS1 and how it is regulated by a protein kinase SOS2 and a calcium binding protein SOS3 were great achievements in the understanding of plant salt resistance. Both tonoplast and plasma membrane antiporters exclude Na+ from the cytosol driven by the proton-motive force generated by the plasma membrane H(+)-ATPase and by the vacuolar membrane H(+)-ATPase and H(+)-pyrophosphatase and it has been shown that the activity of these proteins responds to salinity. In this review we focus on the transcriptional and post-transcriptional regulation by salt of tonoplast proton pumps and Na(+)/H(+) exchangers and on the signalling pathways involved in salt sensing.

Mercury, cadmium and lead biogeochemistry in the soil-plant-insect system in Huludao City

Mercury, cadmium, and lead concentrations of ashed plants and insects samples were investigated and compared with those of soil to reveal their biogeochemical processes along food chains in Huludao City, Liaoning Province, China. Concentration factors of each fragments of the soil-plant-the herbivorous insect-the carnivorous insect food chain were 0.18, 6.57, and 7.88 for mercury; 6.82, 2.01, and 0.48 for cadmium; 1.47, 2.24, and 0.57 for lead, respectively. On the whole, mercury was the most largely biomagnified, but cadmium and lead were not greatly accumulated in the carnivorous insects as expected when the food chain extended to the secondary consumers. Results indicated that concentration factors depended on metals and insects species of food chains.

Post-transcriptional regulation of gene expression in plants during abiotic stress

Land plants are anchored in one place for most of their life cycle and therefore must constantly adapt their growth and metabolism to abiotic stresses such as light intensity, temperature and the availability of water and essential minerals. Thus, plants’ subsistence depends on their ability to regulate rapidly gene expression in order to adapt their physiology to their environment. Recent studies indicate that post-transcriptional regulations of gene expression play an important role in how plants respond to abiotic stresses. We will review the different mechanisms of post-transcriptional regulation of nuclear genes expression including messenger RNA (mRNA) processing, stability, localization and protein translation, and discuss their relative importance for plant adaptation to abiotic stress.

Aluminum stress signaling in plants

Aluminum (Al) toxicity is a major constraint for crop production in acidic soil worldwide. When the soil pH is lower than 5, Al(3+) is released to the soil and enters into root tip cell ceases root development of plant. In acid soil with high mineral content, Al is the major cause of phytotoxicity. The target of Al toxicity is the root tip, in which Al exposure causes inhibition of cell elongation and cell division, leading to root stunting accompanied by reduced water and nutrient uptake. A variety of genes have been identified that are induced or repressed upon Al exposure. At tissue level, the distal part of the transition zone is the most sensitive to Al. At cellular and molecular level, many cell components are implicated in the Al toxicity including DNA in nucleus, numerous cytoplastic compounds, mitochondria, the plasma membrane and the cell wall. Although it is difficult to distinguish the primary targets from the secondary effects so far, understanding of the target sites of the Al toxicity is helpful for elucidating the mechanisms by which Al exerts its deleterious effects on root growth. To develop high tolerance against Al stress is the major goal of plant sciences. This review examines our current understanding of the Al signaling with the physiological, genetic and molecular approaches to improve the crop performance under the Al toxicity. New discoveries will open up new avenues of molecular/physiological inquiry that should greatly advance our understanding of Al tolerance mechanisms. Additionally, these breakthroughs will provide new molecular resources for improving the crop Al tolerance via molecular-assisted breeding and biotechnology.

Protease inhibitors from plants with antimicrobial activity

Antimicrobial proteins (peptides) are known to play important roles in the innate host defense mechanisms of most living organisms, including plants, insects, amphibians and mammals. They are also known to possess potent antibiotic activity against bacteria, fungi, and even certain viruses. Recently, the rapid emergence of microbial pathogens that are resistant to currently available antibiotics has triggered considerable interest in the isolation and investigation of the mode of action of antimicrobial proteins (peptides). Plants produce a variety of proteins (peptides) that are involved in the defense against pathogens and invading organisms, including ribosome-inactivating proteins, lectins, protease inhibitors and antifungal peptides (proteins). Specially, the protease inhibitors can inhibit aspartic, serine and cysteine proteinases. Increased levels of trypsin and chymotrypsin inhibitors correlated with the plants resistance to the pathogen. Usually, the purification of antimicrobial proteins (peptides) with protease inhibitor activity was accomplished by salt-extraction, ultrafiltration and C₁₈ reverse phase chromatography, successfully. We discuss the relation between antimicrobial and anti-protease activity in this review. Protease inhibitors from plants potently inhibited the growth of a variety of pathogenic bacterial and fungal strains and are therefore excellent candidates for use as the lead compounds for the development of novel antimicrobial agents.

Global associations between terrestrial producer and vertebrate consumer diversity

In both ecology and conservation, often a strong positive association is assumed between the diversity of plants as primary producers and that of animals, specifically primary consumers. Such a relationship has been observed at small spatial scales, and a begetting of diversity by diversity is expected under various scenarios of co-evolution and co-adaptation. But positive producer-consumer richness relationships may also arise from similar associations with past opportunities for diversification or contemporary environmental conditions, or from emerging properties of plant diversity such as vegetation complexity or productivity. Here we assess whether the producer-consumer richness relationship generalizes from plot to regional scale and provide a first global test of its strength for vascular plants and endothermic vertebrates. We find strong positive richness associations, but only limited congruence of the most diverse regions. The richness of both primary and higher-level consumers increases with plant richness at similar strength and rate. Environmental conditions emerge as much stronger predictors of consumer richness, and after accounting for environmental differences little variation is explained by plant diversity. We conclude that biotic interactions and strong local associations between plants and consumers only relatively weakly scale up to broad geographical scales and to functionally diverse taxa, for which environmental constraints on richness dominate.

Colloquium paper: species invasions and extinction: the future of native biodiversity on islands

Predation by exotic species has caused the extinction of many native animal species on islands, whereas competition from exotic plants has caused few native plant extinctions. Exotic plant addition to islands is highly nonrandom, with an almost perfect 1 to 1 match between the number of naturalized and native plant species on oceanic islands. Here, we evaluate several alternative implications of these findings. Does the consistency of increase in plant richness across islands imply that a saturation point in species richness has been reached? If not, should we expect total plant richness to continue to increase as new species are added? Finally, is the rarity of native plant extinctions to date a misleading measure of the impact of past invasions, one that hides an extinction debt that will be paid in the future? By analyzing historical records, we show that the number of naturalized plant species has increased linearly over time on many individual islands. Further, the mean ratio of naturalized to native plant species across islands has changed steadily for nearly two centuries. These patterns suggest that many more species will become naturalized on islands in the future. We also discuss how dynamics of invasion bear upon alternative saturation scenarios and the implications these scenarios have for the future retention or extinction of native plant species. Finally, we identify invasion-motivated research gaps (propagule pressure, time-lags to extinction, abundance shifts, and loss of area) that can aid in forecasting extinction and in developing a more comprehensive theory of species extinctions.

A review of traditional plants used in the treatment of epilepsy amongst the Hausa/Fulani tribes of northern Nigeria

Five prescriptions used in the treatment of epilepsy amongst the Hausa/Fulani tribe of Northern Nigeria were collected from traditional healers. The five prescriptions containing eight plants were reviewed as in literature to ascertain scientific basis of their use in treatment of epilepsy. Securidaca longipedunculata (family Polygalaceace) was reported to have such property; Mitragyna inermis (family Rubiaceae) has alkaloids structurally similar to clinically useful anticonvulsant. Celtis integrefolia (family Ulmaceae) was reported to contain gamma amino butyric acid (GABA) that its deficiency may lead to convulsions. The remaining plants were basically helpful in alleviation of associated symptoms of epilepsy except Centaurea praecox (family Asteraceae) which was reported to have neurotoxic substances that may worsen the disease.

Carbon monoxide: A novel and pivotal signal molecule in plants?

Carbon monoxide (CO), a by-product released during the degradation of heme by heme oxygenases (HOS EC 1.14.99.3) in animals, plays a major role as neurotransmitter, regulator of sinusoidal tone, inhibitor of platelet aggregation and suppressor of acute hypertensive response, and most of above effects are similar to or mediated by nitric oxide (NO), another signal molecule in both the animal and plant kingdoms. Previous result demonstrated that NO could act as a promoter of plant cell elongation, acting similarly to IAA, inducing morphogenetic responses leading to expansion in plant tissues. Recent observations revealed that CO is an inducer of cell expansion in wheat root segments, acting similarly to IAA and NO. Evidence also indicated that IAA could result in either the potent induction of HO-1 transcript or endogenous CO releasing in wheat root segments. Additionally, our results suggested that above CO signaling might be related to NO/cGMP, Ca(2+) and even ROS-dependent pathways. In this addendum, combined with other previous results, we further proposed a possible hypothesis for CO signaling role in regulation of plant root development induced by auxin.

A three-dimensional statistical reconstruction model of grapevine (Vitis vinifera) simulating canopy structure variability within and between cultivar/training system pairs

BACKGROUND AND AIMS

In grapevine, canopy-structure-related variations in light interception and distribution affect productivity, yield and the quality of the harvested product. A simple statistical model for reconstructing three-dimensional (3D) canopy structures for various cultivar-training system (C x T) pairs has been implemented with special attention paid to balance the time required for model parameterization and accuracy of the representations from organ to stand scales. Such an approach particularly aims at overcoming the weak integration of interplant variability using the usual direct 3D measurement methods.

MODEL

This model is original in combining a turbid-medium-like envelope enclosing the volume occupied by vine shoots with the use of discrete geometric polygons representing leaves randomly located within this volume to represent plant structure. Reconstruction rules were adapted to capture the main determinants of grapevine shoot architecture and their variability. Using a simplified set of parameters, it was possible to describe (1) the 3D path of the main shoot, (2) the volume occupied by the foliage around this path and (3) the orientation of individual leaf surfaces. Model parameterization (estimation of the probability distribution for each parameter) was carried out for eight contrasting C x T pairs.

KEY RESULTS AND CONCLUSIONS

The parameter values obtained in each situation were consistent with our knowledge of grapevine architecture. Quantitative assessments for the generated virtual scenes were carried out at the canopy and plant scales. Light interception efficiency and local variations of light transmittance within and between experimental plots were correctly simulated for all canopies studied. The approach predicted these key ecophysiological variables significantly more accurately than the classical complete digitization method with a limited number of plants. In addition, this model accurately reproduced the characteristics of a wide range of individual digitized plants. Simulated leaf area density and the distribution of light interception among leaves were consistent with measurements. However, at the level of individual organs, the model tended to underestimate light interception.

The plant sHSP superfamily: five new members in Arabidopsis thaliana with unexpected properties

The small heat shock proteins (sHsps), which are ubiquitous stress proteins proposed to act as chaperones, are encoded by an unusually complex gene family in plants. Plant sHsps are classified into different subfamilies according to amino acid sequence similarity and localization to distinct subcellular compartments. In the whole Arabidopsis thaliana genome, 19 genes were annotated to encode sHsps, of which 14 belong to previously defined plant sHsp families. In this paper, we report studies of the five additional sHsp genes in A. thaliana, which can now be shown to represent evolutionarily distinct sHsp subfamilies also found in other plant species. While two of these five sHsps show expression patterns typical of the other 14 genes, three have unusual tissue specific and developmental profiles and do not respond to heat induction. Analysis of intracellular targeting indicates that one sHsp represents a new class of mitochondrion-targeted sHsps, while the others are cytosolic/nuclear, some of which may cooperate with other sHsps in formation of heat stress granules. Three of the five new proteins were purified and tested for chaperone activity in vitro. Altogether, these studies complete our basic understanding of the sHsp chaperone family in plants.

Phytoremediative capacity of plants enriched with melatonin

Melatonin is an environmentally friendly-molecule with broad spectrum antioxidant capacity. Melatonin is widely present in the plant kingdom. High levels of melatonin exist in an aquatic plant, the water hyacinth, which is highly tolerant of environmental pollutants. Elevated levels of melatonin probably help plants to protect against environmental stress caused by water and soil pollutants. To investigate the potential relationships between melatonin supplementation and environmental tolerance in plants, pea plants were treated with high levels of copper in the soil. The results show that copper contamination kills pea plants; however, melatonin added to the soil significantly enhanced their tolerance to the copper contamination and, therefore, increased their survival. Based on the theory and these preliminary data, we speculate that melatonin could be used to improve the phytoremediative efficiency of plants against different pollutants. Since melatonin is safe to animals and humans as well as being inexpensive, it may be a feasible and cost-effective approach to clean environmental contaminations.

Pharmacological evidence for calcium involvement in the long-term processing of abiotic stimuli in plants

Information about abiotic conditions is stored for long periods in plants and, in flax seedlings, can lead to the production of meristems. To investigate the underlying mechanism, flax seedlings were given abiotic stimuli that included a mechanical stimulus (by manipulation), one or two cold shocks, a slow cold treatment and a drought stress and, if these seedlings were then subjected to a temporary (1 to 3 days) depletion of calcium, epidermal meristems were produced in the seedling hypocotyls. This production was inhibited by the addition to the nutrient media of EGTA, ruthenium red, lanthanum or gadolinium that affect calcium availability or calcium transport. Use of these agents revealed a period of vulnerability in information processing that was less than two min for mechanical stimuli and over five min for other abiotic stimuli, consistent with information about mechanical stimuli being stored particularly fast. We propose that external calcium is needed for the transduction/storage of the information for meristem production whilst a temporary depletion of external calcium is needed for the actual production of meristems. Such roles for calcium would be consistent with a mechanism based on ion condensation on charged polymers.

Chloroplast envelope membranes: a dynamic interface between plastids and the cytosol

Chloroplasts are bounded by a pair of outer membranes, the envelope, that is the only permanent membrane structure of the different types of plastids. Chloroplasts have had a long and complex evolutionary past and integration of the envelope membranes in cellular functions is the result of this evolution. Plastid envelope membranes contain a wide diversity of lipids and terpenoid compounds serving numerous biochemical functions and the flexibility of their biosynthetic pathways allow plants to adapt to fluctuating environmental conditions (for instance phosphate deprivation). A large body of knowledge has been generated by proteomic studies targeted to envelope membranes, thus revealing an unexpected complexity of this membrane system. For instance, new transport systems for metabolites and ions have been identified in envelope membranes and new routes for the import of chloroplast-specific proteins have been identified. The picture emerging from our present understanding of plastid envelope membranes is that of a key player in plastid biogenesis and the co-ordinated gene expression of plastid-specific protein (owing to chlorophyll precursors), of a major hub for integration of metabolic and ionic networks in cell metabolism, of a flexible system that can divide, produce dynamic extensions and interact with other cell constituents. Envelope membranes are indeed one of the most complex and dynamic system within a plant cell. In this review, we present an overview of envelope constituents together with recent insights into the major functions fulfilled by envelope membranes and their dynamics within plant cells.

Escherichia coli as a platform for functional expression of plant P450 carotene hydroxylases

Carotenoids and their derivatives are essential for growth, development, and signaling in plants and have an added benefit as nutraceuticals in food crops. Despite the importance of the biosynthetic pathway, there remain open questions regarding some of the later enzymes in the pathway. The CYP97 family of P450 enzymes was predicted to function in carotene ring hydroxylation, to convert provitamin A carotenes to non-provitamin A xanthophylls. However, substrate specificity was difficult to investigate directly in plants, which mask enzyme activities by a complex and dynamic metabolic network. To characterize the enzymes more directly, we amplified cDNAs from a model crop, Oryza sativa, and used functional complementation in Escherichia coli to test activity and specificity of members of Clans A and C. This heterologous system will be valuable for further study of enzyme interactions and substrate utilization needed to understand better the role of CYP97 hydroxylases in plant carotenoid biosynthesis.

Expression of Aedes trypsin-modulating oostatic factor on the virion of TMV: A potential larvicide

We report the engineering of the surface of the tobacco mosaic virus (TMV) virion with a mosquito decapeptide hormone, trypsin-modulating oostatic factor (TMOF). The TMV coat protein (CP) was fused to TMOF at the C terminus by using a read-through, leaky stop codon that facilitated expression of CP and chimeric CP-TMOF (20:1 ratio) that were coassembled into virus particles in infected Nicotiana tabacum. Plants that were infected with the hybrid TMV RNA accumulated TMOF to levels of 1.3% of total soluble protein. Infected tobacco leaf discs that were fed to Heliothis virescens fourth-instar larvae stunted their growth and inhibited trypsin and chymotrypsin activity in their midgut. Purified CP-TMOF virions fed to mosquito larvae stopped larval growth and caused death. Because TMV has a wide host range, expressing TMV-TMOF in plants can be used as a general method to protect them against agricultural insect pests and to control vector mosquitoes.

The occurrence of hormesis in plants and algae

This paper evaluated the frequency, magnitude and dose/concentration range of hormesis in four species: The aquatic plant Lemna minor, the micro-alga Pseudokirchneriella subcapitata and the two terrestrial plants Tripleurospermum inodorum and Stellaria media exposed to nine herbicides and one fungicide and binary mixtures thereof. In total 687 dose-response curves were included in the database. The study showed that both the frequency and the magnitude of the hormetic response depended on the endpoint being measured. Dry weight at harvest showed a higher frequency and a larger hormetic response compared to relative growth rates. Evaluating hormesis for relative growth rates for all species showed that 25% to 76% of the curves for each species had treatments above 105% of the control. Fitting the data with a dose-response model including a parameter for hormesis showed that the average growth increase ranged from 9+/-1% to 16+/-16% of the control growth rate, while if measured on a dry weight basis the response increase was 38+/-13% and 43+/-23% for the two terrestrial species. Hormesis was found in >70% of the curves with the herbicides glyphosate and metsulfuron-methyl, and in >50% of the curves for acifluorfen and terbuthylazine. The concentration ranges of the hormetic part of the dose-response curves corresponded well with literature values.

Arsenic contamination in food-chain: transfer of arsenic into food materials through groundwater irrigation

Arsenic contamination in groundwater in Bangladesh has become an additional concern vis-à-vis its use for irrigation purposes. Even if arsenic-safe drinking-water is assured, the question of irrigating soils with arsenic-laden groundwater will continue for years to come. Immediate attention should be given to assess the possibility of accumulating arsenic in soils through irrigation-water and its subsequent entry into the food-chain through various food crops and fodders. With this possibility in mind, arsenic content of 2,500 water, soil and vegetable samples from arsenic-affected and arsenic-unaffected areas were analyzed during 1999-2004. Other sources of foods and fodders were also analyzed. Irrigating a rice field with groundwater containing 0.55 mg/L of arsenic with a water requirement of 1,000 mm results in an estimated addition of 5.5 kg of arsenic per ha per annum. Concentration of arsenic as high as 80 mg per kg of soil was found in an area receiving arsenic-contaminated irrigation. A comparison of results from affected and unaffected areas revealed that some commonly-grown vegetables, which would usually be suitable as good sources of nourishment, accumulate substantially-elevated amounts of arsenic. For example, more than 150 mg/kg of arsenic has been found to be accumulated in arum (kochu) vegetable. Implications of arsenic ingested in vegetables and other food materials are discussed in the paper.

Memory processes in the response of plants to environmental signals

Plants are sensitive to stimuli from the environment (e.g., wind, rain, contact, pricking, wounding). They usually respond to such stimuli by metabolic or morphogenetic changes. Sometimes the information corresponding to a stimulus may be "stored" in the plant where it remains inactive until a second stimulus "recalls" this information and finally allows it to take effect. Two experimental systems have proved especially useful in unravelling the main features of these memory-like processes.In the system based on Bidens seedlings, an asymmetrical treatment (e.g., pricking, or gently rubbing one of the seedling cotyledons) causes the cotyledonary buds to grow asymmetrically after release of apical dominance by decapitation of the seedlings. This information may be stored within the seedlings, without taking effect, for at least two weeks; then the information may be recalled by subjecting the seedlings to a second, appropriate, treatment that permits transduction of the signal into the final response (differential growth of the buds). Whilst storage is an irreversible, all-or-nothing process, recall is sensitive to a number of factors, including the intensity of these factors, and can readily be enabled or disabled. In consequence, it is possible to recall the stored message several times successively.In the system based on flax seedlings, stimulation such as manipulation stimulus, drought, wind, cold shock and radiation from a GSM telephone or from a 105 GHz Gunn oscillator, has no apparent effect. If, however, the seedlings are subjected at the same time to transient calcium depletion, numerous epidermal meristems form in their hypocotyls. When the calcium depletion treatment is applied a few days after the mechanical treatment, the time taken for the meristems to appear is increased by a number of days exactly equal to that between the application of the mechanical treatment and the beginning of the calcium depletion treatment. This means that a meristem-production information corresponding to the stimulation treatment has been stored in the plants, without any apparent effect, until the calcium depletion treatment recalls this information to allow it to take effect. Gel electrophoresis has shown that a few protein spots are changed (pI shift, appearance or disappearance of a spot) as a consequence of the application of the treatments that store or recall a meristem-production signal in flax seedlings. A SIMS investigation has revealed that the pI shift of one of these spots is probably due to protein phosphorylation. Modifications of the proteome have also been observed in Arabidopsis seedlings subjected to stimuli such as cold shock or radiation from a GSM telephone.

Individual-based modelling: potentials and limitations

Individual-based modelling (IBM) is an important option in ecology for the study of specific properties of complex ecological interaction networks. The main application of this model type is the analysis of population characteristics at high resolution. IBM also contributes to the advancement of ecological theory. One of the remarkable potentials of the approach is the possibility of studying self-organization and emergent properties that arise from individual actions on higher integration levels, especially on the population level. This review outlines the background and different application fields of individual-based models together with a short description of the technical implications of model setup. The limitations of this modelling approach result from the technical basis of model construction, which can handle a limited number of active entities only. Limits in biological knowledge also restrict the application of this model type. The paper presents some individual-based models that have been developed for different purposes and briefly discusses these models. Concerning the perspective of IBM, a coincidence with developments in artificial life research is explained. IBM shifts the focus of ecological analysis of dynamic systems from structurally fixed settings to the analysis of self-organizing interaction patterns that are variable in quantity and quality.

Arabidopsis and the Genetic Potential for the Phytoremediation of Toxic Elemental and Organic Pollutants

In a process called phytoremediation, plants can be used to extract, detoxify, and/or sequester toxic pollutants from soil, water, and air. Phytoremediation may become an essential tool in cleaning the environment and reducing human and animal exposure to potential carcinogens and other toxins. Arabidopsis has provided useful information about the genetic, physiological, and biochemical mechanisms behind phytoremediation, and it is an excellent model genetic organism to test foreign gene expression. This review focuses on Arabidopsis studies concerning: 1) the remediation of elemental pollutants; 2) the remediation of organic pollutants; and 3) the phytoremediation genome. Elemental pollutants include heavy metals and metalloids (e.g., mercury, lead, cadmium, arsenic) that are immutable. The general goal of phytoremediation is to extract, detoxify, and hyperaccumulate elemental pollutants in above-ground plant tissues for later harvest. A few dozen Arabidopsis genes and proteins that play direct roles in the remediation of elemental pollutants are discussed. Organic pollutants include toxic chemicals such as benzene, benzo(a)pyrene, polychlorinated biphenyls, trichloroethylene, trinitrotoluene, and dichlorodiphenyltrichloroethane. Phytoremediation of organic pollutants is focused on their complete mineralization to harmless products, however, less is known about the potential of plants to act on complex organic chemicals. A preliminary survey of the Arabidopsis genome suggests that as many as 700 genes encode proteins that have the capacity to act directly on environmental pollutants or could be modified to do so. The potential of the phytoremediation proteome to be used to reduce human exposure to toxic pollutants appears to be enormous and untapped.

Ozone and plants: need for a biologically based air quality standard

For the past 10 years, I have spent parts of late July and early August in central Europe, assessing ozone injury symptom expression on native plants in upland meadows and along forest edges. Much of this work has been done with local colleagues in and near the Tatra Mountains in southern Poland and eastern Slovakia and in the Carpathian Mountains in western Ukraine. Active and passive ozone air monitors and samplers were also used at most of the study sites.

Nitrogen in the environment: sources, problems, and management

Nitrogen (N) is applied worldwide to produce food. It is in the atmosphere, soil, and water and is essential to all life. N for agriculture includes fertilizer, biologically fixed, manure, recycled crop residue, and soil-mineralized N. Presently, fertilizer N is a major source of N, and animal manure N is inefficiently used. Potential environmental impacts of N excreted by humans are increasing rapidly with increasing world populations. Where needed, N must be efficiently used because N can be transported immense distances and transformed into soluble and/or gaseous forms that pollute water resources and cause greenhouse effects. Unfortunately, increased amounts of gaseous N enter the environment as N2O to cause greenhouse warming and as NH3 to shift ecological balances of natural ecosystems. Large amounts of N are displaced with eroding sediments in surface waters. Soluble N in runoff or leachate water enters streams, rivers, and groundwater. High-nitrate drinking water can cause methemoglobinemia, while nitrosamines are associated with various human cancers. We describe the benefits, but also how N in the wrong form or place results in harmful effects on humans and animals, as well as to ecological and environmental systems.

Nuclear events in ethylene signaling: a transcriptional cascade mediated by ETHYLENE-INSENSITIVE3 and ETHYLENE-RESPONSE-FACTOR1

Response to the gaseous plant hormone ethylene in Arabidopsis requires the EIN3/EIL family of nuclear proteins. The biochemical function(s) of EIN3/EIL proteins, however, has remained unknown. In this study, we show that EIN3 and EILs comprise a family of novel sequence-specific DNA-binding proteins that regulate gene expression by binding directly to a primary ethylene response element (PERE) related to the tomato E4-element. Moreover, we identified an immediate target of EIN3, ETHYLENE-RESPONSE-FACTOR1 (ERF1), which contains this element in its promoter. EIN3 is necessary and sufficient for ERF1 expression, and, like EIN3-overexpression in transgenic plants, constitutive expression of ERF1 results in the activation of a variety of ethylene response genes and phenotypes. Evidence is also provided that ERF1 acts downstream of EIN3 and all other components of the ethylene signaling pathway. The results demonstrate that the nuclear proteins EIN3 and ERF1 act sequentially in a cascade of transcriptional regulation initiated by ethylene gas.

Tansley Review No. 95 15 N natural abundance in soil-plant systems

Equilibrium and kinetic isotope fractionations during incomplete reactions result in minute differences in the ratio between the two stable X isotopes, ¹⁵ N and ¹⁴ N, in various N pools. In ecosystems such variations (usually expressed in per mil [δ¹⁵ N] deviations from the standard atmospheric N₂ ) depend on isotopic signatures of inputs and outputs, the input-output balance, N transformations and their specific isotope effects, and compartmentation of N within the system. Products along a sequence of reactions, e.g. the N mineralization-N uptake pathway, should, if fractionation factors were equal for the different reactions, become progressively depleted. However, fractionation factors van. For example, because nitrification discriminates against ¹⁵ N in the substrate more than does N mineralization, NH₄ ⁺ can become isotopically heavier than the organic N from which it is derived. Levels of isotopic enrichment depend dynamically on the stoichiometry of reactions, as well as on specific abiotic and biotic conditions. Thus, the δ¹⁵ N of a specific N pool is not a constant, and ¹⁵ N of a N compound added to the system is not a conservative, unchanging tracer. This fact, together with analytical problems of measuring ¹⁵ N in small and dynamic pools of N in the soil-plant system, and the complexity of the X cycle itself (for instance the abundance of reversible reactions), limit the possibilities of making inferences based on observations of ¹⁵ N abundance in one or a few pools of N in a system. Nevertheless, measurements of δ¹⁵ N might offer the advantage of giving insights into the N cycle without disturbing the system by adding ¹⁵ N tracer. Such attempts require, however, that the complex factors affecting ¹⁵ N in plants be taken into account, viz. (i) the source(s) of N (soil, precipitation, NO_X , NH₃ , N₂ -fixation), (ii) the depth(s) in soil from which N is taken up, (iii) the form(s) of soil-N used (organic N, NH₄ ⁺ , NO₃ ^- ), (iv) influences of mycorrhizal symbioses and fractionations during and after N uptake by plants, and (v) interactions between these factors and plant phenology. Because of this complexity, data on δ¹⁵ N can only be used alone when certain requirements are met, e.g. when a clearly discrete N source in terms of amount and isotopic signature is studied. For example, it is recommended that N in non-N₂ -fixing species should differ more than 5% from N derived by N₂ -fixation, and that several non-N₂ -fixing references are used, when data on δ¹⁵ N are used to estimate N_a -fixation in poorly described ecosystems. As well as giving information on N source effects, δ¹⁵ N can give insights into N cycle rates. For example, high levels of N deposition onto previously N-limited systems leads to increased nitrification, which produces ¹⁵ N-enriched NH₄ and N-depleted NO₃ . As many forest plants prefer NH₄ ^- they become enriched in ¹⁵ N in such circumstances. This change in plant ¹⁵ N will subsequently also occur in the soil surface horizon after litter-fall, and might be a useful indicator of N saturation, especially since there is usually an increase in ¹⁵ N with depth in soils of N-limited forests. Generally, interpretation of ¹⁵ N measurements requires additional independent data and modelling, and benefits from a controlled experimental setting. Modelling will be greatly assisted by the development of methods to measure the ¹⁵ N of small dynamic pools of N in soils. Direct comparisons with parallel low tracer level ¹⁵ N studies will be necessary to further develop the interpretation of variations in ¹⁵ N in soil-plant systems. Another promising approach is to study ratios of ¹⁵ N: ¹⁴ N together with other pairs of stable isotopes, e.g. ¹³ C: ¹² C or ¹⁸ O:¹⁶ O, in the same ion or molecules. This approach can help to tackle the challenge of distinguishing isotopic source effects from fractionations within the system studied. CONTENTS Summary 179 I. Introduction 180 II. Units, causes of isotope effects, stoichiometry, modelling 181 III. N dynamics and variations in ¹⁵ N abundance in soil-plant systems 183 IV. Applications 189 V. Conclusions and suggestions for future research 197 Acknowledgements 198 References 198.

The distribution of genes in the genomes of Gramineae

Recent investigations showed that most maize genes are present in compositional fractions of nuclear DNA that cover only a 1-2% GC (molar fraction of guanosine plus cytosine in DNA) range and represent only 10-20% of the genome. These fractions, which correspond to compositional genome compartments that are distributed on all chromosomes, were collectively called the "gene space." Outside the gene space, the maize genome appears to contain no genes, except for some zein genes and for ribosomal genes. Here, we investigated the distribution of genes in the genomes of two other Gramineae, rice and barley, and used a new set of probes to study further the gene distribution of maize. We found that the distribution of genes in these three genomes is basically similar in that all genes, except for ribosomal genes and some storage protein genes, were located in gene spaces that (i) cover GC ranges of 0.8%, 1.0%, and 1.6% and represent 12%, 17%, and 24% of the genomes of barley, maize, and rice, respectively; (ii) are due to a remarkably uniform base composition in the sequences surrounding the genes, which are now known to consist mainly of transposons; (iii) have sizes approximately proportional to genome sizes, suggesting that expansion-contraction phenomena proceed in parallel in the gene space and in the gene-empty regions of the genome; and (iv) only hybridize on the gene spaces (and not on the other DNA fractions) of other Gramineae.

Incidence and Sources of Listeria monocytogenes in Cold-Smoked Fishery Products and Processing Plants

Cold-smoked salmon processing plants were surveyed to determine the occurrence and sources of L. monocytogenes contamination. Sanitation and cleanup procedures adequately eliminated L. monocytogenes from the processing line and equipment, but recontamination occurred soon after resumption of processing. The primary source of contamination proved to be the surface areas of frozen or fresh raw fish coming into the plant. Listeria species were not isolated from the flesh except when they were introduced during the filleting operation, by the injection of recirculated brine, or in localized areas where there were pre-existing bruises. Penetration of L. monocytogenes into intact flesh via the vascular system did not occur when fresh fish were immobilized with carbon dioxide and bled, nor when frozen, headed, and eviscerated fish were thawed for 20 h in water inoculated with 44 L. monocytogenes organisms per ml. Populations of L. monocytogenes inoculated onto the surface of brined salmon portions changed very little during a cold-smoke process at 72 to 87°F (22.2 to 30.6°C) for 20 h, with or without applied smoke; but when the processing temperature was lowered to 63 to 70°F (17.2 to 21.1°C), populations decreased 10- to 25-fold when smoke was applied. L. monocytogenes injected into the interior of these portions increased 2- to 6-fold at 63 to 70°F (17.2 to 21.1°C) and 100-fold at 72 to 87°F (22.2 to 30.6°C), regardless of the presence of smoke. L. monocytogenes was enumerated in 48 contaminated finished products collected from six different processing plants. L. monocytogenes populations ranged from 0.3 to 34.3 cells per g, with a mean of 6.2 per g and a median of 3.2 per g.

Actin in the green alga, Nitella

Bundles of microfilaments very similar in appearance to actin are present in cytoplasmic suspensions obtained from Nitella flexilis. The microfilaments bind rabbit heavy meromyosin in arrowhead arrays similar to those produced on muscle actin. The arrowheads are removed with ATP. The results provide evidence that actin is present in green plants, probably in the form of microfilaments thought to be involved in cytoplasmic streaming.