Anatomical changes on coffee leaves infected by Pseudomonas syringae pv. garcae

ABSTRACTAlthough poorly studied, the bacterial halo blight is an important disease in the major coffee-producing states of Brazil. External damage and anatomical changes on leaves were measured in seedlings of Coffea arabica cv. Mundo Novo, susceptible to Pseudomonas syringae pv. garcae, by using histological sections obtained at 10 and 20 days after inoculation (DAI). The changes on the epidermis were smaller than the lesions measured in the mesophyll, irrespective of the evaluated colonization period, showing that the internal damage caused by the bacterium represent twice the damage observed externally. From the inoculation site, lysis occurred on the epidermal cells and on the palisade and spongy parenchyma cells, with strong staining of their cellular contents, as well as abnormal intercellular spaces in the palisade parenchyma, hypertrophy and hyperplasia of mesophyll cells and partial destruction of chloroplasts. Additionally, this study revealed the presence of inclusion bodies in epidermal and mesophyll cells. Bacterial masses were found in the apoplast between and within mesophyll cells. Bacteria were also observed in the bundle sheath and vascular bundles and were more pronounced at 20 DAI, not only near the inoculation site but also in distant areas, suggesting displacement through the vascular system. These results can be useful to understand this plant-pathogen interaction.

Quantifying seed production by volunteer canola (Brassica napus) and Sinapis arvensis

Volunteer canola (Brassica napus) and Sinapis arvensis are well identified weeds of different cropping systems. Quantitative information on regarding seed production by them is limited. Such information is necessary to model dynamics of soil seed banks. The aim of this work was to quantify seed production as a function of the size of those weeds. A wide range of plant size was produced by using a fan seeding system performed at two sowing dates (environments). Plant size varied from 3 to 167 g per plant for canola and from 6 to 104 g per plant for S. arvensis. Seed production ranged from 543 to14,773 seeds per plant for canola, and from 264 to 10,336 seeds per plant for S. arvensis. There was a close relationship between seed production per plant and plant size which was well-described by a power function (y = 130.6x0.94; R² = 0.93 for canola and y = 28x1.27; R² = 0.95 for S. arvensis). There was also strong relationships among the number of pods produced in individual plants and the quantity of seeds produced (g per plant) with the size of the plant. The relationships found in this study can be used in dynamic seed bank models of volunteer canola and S. arvensis.

Expression and cytokine secretion in the states of immune reactivation in leprosy

Leprosy is a chronic inflammatory disease caused by Mycobacterium leprae. The human response to this pathogen exhibits intriguing aspects which are up to now not well understood. The present study discusses the probable mechanisms involved in T cell-specific unresponsiveness observed in lepromatous patients. Analysis of the cytokine profile either in blood leukocytes or in skin specimens taken from leprosy lesions indicates that some parameters of Th1 immune response are present in lepromatous patients under reactional states

Genomics and X-ray microanalysis indicate that Ca2+ and thiols mediate the aggregation and adhesion of Xylella fastidiosa

The availability of the genome sequence of the bacterial plant pathogen Xylella fastidiosa, the causal agent of citrus variegated chlorosis, is accelerating important investigations concerning its pathogenicity. Plant vessel occlusion is critical for symptom development. The objective of the present study was to search for information that would help to explain the adhesion of X. fastidiosa cells to the xylem. Scanning electron microscopy revealed that adhesion may occur without the fastidium gum, an exopolysaccharide produced by X. fastidiosa, and X-ray microanalysis demonstrated the presence of elemental sulfur both in cells grown in vitro and in cells found inside plant vessels, indicating that the sulfur signal is generated by the pathogen surface. Calcium and magnesium peaks were detected in association with sulfur in occluded vessels. We propose an explanation for the adhesion and aggregation process. Thiol groups, maintained by the enzyme peptide methionine sulfoxide reductase, could be active on the surface of the bacteria and appear to promote cell-cell aggregation by forming disulfide bonds with thiol groups on the surface of adjacent cells. The enzyme methionine sulfoxide reductase has been shown to be an auxiliary component in the adhesiveness of some human pathogens. The negative charge conferred by the ionized thiol group could of itself constitute a mechanism of adhesion by allowing the formation of divalent cation bridges between the negatively charged bacteria and predominantly negatively charged xylem walls.

Mapping and signaling of neural pathways involved in the regulation of hydromineral homeostasis

Several forebrain and brainstem neurochemical circuitries interact with peripheral neural and humoral signals to collaboratively maintain both the volume and osmolality of extracellular fluids. Although much progress has been made over the past decades in the understanding of complex mechanisms underlying neuroendocrine control of hydromineral homeostasis, several issues still remain to be clarified. The use of techniques such as molecular biology, neuronal tracing, electrophysiology, immunohistochemistry, and microinfusions has significantly improved our ability to identify neuronal phenotypes and their signals, including those related to neuron-glia interactions. Accordingly, neurons have been shown to produce and release a large number of chemical mediators (neurotransmitters, neurohormones and neuromodulators) into the interstitial space, which include not only classic neurotransmitters, such as acetylcholine, amines (noradrenaline, serotonin) and amino acids (glutamate, GABA), but also gaseous (nitric oxide, carbon monoxide and hydrogen sulfide) and lipid-derived (endocannabinoids) mediators. This efferent response, initiated within the neuronal environment, recruits several peripheral effectors, such as hormones (glucocorticoids, angiotensin II, estrogen), which in turn modulate central nervous system responsiveness to systemic challenges. Therefore, in this review, we shall evaluate in an integrated manner the physiological control of body fluid homeostasis from the molecular aspects to the systemic and integrated responses.

Plant lectins, chemical and biological aspects

Lectins, carbohydrate-binding proteins of non-immune origin, that agglutinate cells or precipitate polysaccharides and glycoconjugates, are well distributed in nature, mainly in the Plant Kingdom. The great majority of the plante lectins are present in seed cotyledons where they are found in the cytoplasm or int he protein bodies, although they have also been found in roots, stems and leaves. Due to their peculiar properties, the lectins are used as a tool both for analytical and preparative purposes in biochemistry, cellular biology, immunology and related areas. In agriculture and medicine the use of lectins greatly improved in the last few years. The lextins, with few exceptions, are glycoproteins, need divalent cations to display full activity and are, in general, oligomers with variable molecular weight. Although the studies on lectins have completed a century, their role in nature is yet ynknown . Several hypotheses on their physiological functions have been suggested. Thus, lectins could play important roles in defense against pathogens, plant-microorganism symbiosis, cell organization, embryo morphogenesis, phagocytosis, cell wall elongation, pollen recognition and as reserve proteins. A brief review on the general properties and roles of the lectins is given.

Molecular battles between plant and pathogenic bacteria in the phyllosphere

The phyllosphere, i.e., the aerial parts of the plant, provides one of the most important niches for microbial colonization. This niche supports the survival and, often, proliferation of microbes such as fungi and bacteria with diverse lifestyles including epiphytes, saprophytes, and pathogens. Although most microbes may complete the life cycle on the leaf surface, pathogens must enter the leaf and multiply aggressively in the leaf interior. Natural surface openings, such as stomata, are important entry sites for bacteria. Stomata are known for their vital role in water transpiration and gas exchange between the plant and the environment that is essential for plant growth. Recent studies have shown that stomata can also play an active role in limiting bacterial invasion of both human and plant pathogenic bacteria as part of the plant innate immune system. As counter-defense, plant pathogens such as Pseudomonas syringae pv tomato (Pst) DC3000 use the virulence factor coronatine to suppress stomate-based defense. A novel and crucial early battleground in host-pathogen interaction in the phyllosphere has been discovered with broad implications in the study of bacterial pathogenesis, host immunity, and molecular ecology of bacterial diseases.

Immunological aspects of host-schistosome relationships

The complex immunological relationships between schistosomes and their vertebrate hosts are considered to be conveniently divisible into four distinct, though interrelated categories: the parasite's vulnerability to, its evasion of, and its exploitation of the host's immune response, and its stimulation of the host's immune response to produce immunopathology. Some significant recent advances in the first three categories are discussed, as well as their relationships to the fourth category of immunopathology.

The use of biodiversity as source of new chemical entities against defined molecular targets for treatment of malaria, tuberculosis, and T-cell mediated diseases: a review

The modern approach to the development of new chemical entities against complex diseases, especially the neglected endemic diseases such as tuberculosis and malaria, is based on the use of defined molecular targets. Among the advantages, this approach allows (i) the search and identification of lead compounds with defined molecular mechanisms against a defined target (e.g. enzymes from defined pathways), (ii) the analysis of a great number of compounds with a favorable cost/benefit ratio, (iii) the development even in the initial stages of compounds with selective toxicity (the fundamental principle of chemotherapy), (iv) the evaluation of plant extracts as well as of pure substances. The current use of such technology, unfortunately, is concentrated in developed countries, especially in the big pharma. This fact contributes in a significant way to hamper the development of innovative new compounds to treat neglected diseases. The large biodiversity within the territory of Brazil puts the country in a strategic position to develop the rational and sustained exploration of new metabolites of therapeutic value. The extension of the country covers a wide range of climates, soil types, and altitudes, providing a unique set of selective pressures for the adaptation of plant life in these scenarios. Chemical diversity is also driven by these forces, in an attempt to best fit the plant communities to the particular abiotic stresses, fauna, and microbes that co-exist with them. Certain areas of vegetation (Amazonian Forest, Atlantic Forest, Araucaria Forest, Cerrado-Brazilian Savanna, and Caatinga) are rich in species and types of environments to be used to search for natural compounds active against tuberculosis, malaria, and chronic-degenerative diseases. The present review describes some strategies to search for natural compounds, whose choice can be based on ethnobotanical and chemotaxonomical studies, and screen for their ability to bind to immobilized drug targets and to inhibit their activities. Molecular cloning, gene knockout, protein expression and purification, N-terminal sequencing, and mass spectrometry are the methods of choice to provide homogeneous drug targets for immobilization by optimized chemical reactions. Plant extract preparations, fractionation of promising plant extracts, propagation protocols and definition of in planta studies to maximize product yield of plant species producing active compounds have to be performed to provide a continuing supply of bioactive materials. Chemical characterization of natural compounds, determination of mode of action by kinetics and other spectroscopic methods (MS, X-ray, NMR), as well as in vitro and in vivo biological assays, chemical derivatization, and structure-activity relationships have to be carried out to provide a thorough knowledge on which to base the search for natural compounds or their derivatives with biological activity.

Molecular detection of human astrovirus in an urban sewage treatment plant in Rio de Janeiro, Brazil

The objective of this study was to evaluate the prevalence and dissemination of human astroviruses (HAstV) in the environment by analyzing urban sewage samples from a wastewater treatment plant in the city of Rio de Janeiro, Brazil. A one-year study was performed with a total of 48 raw and treated sewage composite samples, which were collected biweekly from an activated sludge plant. Virus particles were concentrated by the adsorption-elution method using negatively charged membranes associated to a Centriprep Concentrator® 50 (Nihon Millipore). HAstV were detected in 16.7% of the samples in raw and treated sewage by using both qualitative and quantitative reverse transcriptase-polymerase chain reactions (RT-PCR and qPCR, respectively). Positive untreated sewage sample exhibited mean values of 1.1 x 10(4) gEq/mL. The qPCR sensitivity was 18 gEq/reaction. Through utilization of qPCR, a HAstV recovery efficiency of 4.2% and 4.3% was demonstrated for raw and treated sewage samples, respectively. The presence of HAstV in both the raw and treated sewage samples demonstrated the dissemination of these viruses in the environment as well as viral permanence after sewage treatment. There was a reduction in the total and faecal coliform levels, indicating efficiency of the wastewater treatment plant.

Molecular approaches for eco-epidemiological studies of Paracoccidioides brasiliensis

Medical mycology has greatly benefited from the introduction of molecular techniques. New knowledge on molecular genetics has provided both theoretical and practical frameworks, permitting important advances in our understanding of several aspects of pathogenic fungi. Considering Paracoccidioides brasiliensis in particular, important eco-epidemiological aspects, such as environmental distribution and new hosts were clarified through molecular approaches. These methodologies also contributed to a better understanding about the genetic variability of this pathogen; thus, P. brasiliensis is now assumed to represent a species complex. The present review focuses on some recent findings about the current taxonomic status of P. brasiliensis, its phylogenetic and speciation processes, as well as on some practical applications for the molecular detection of this pathogen in environmental and clinical materials.

Phylogenetic relationships among four species of the guarani group of Drosophila (Diptera, Drosophilidae) as inferred by molecular and morphological analyses

Traditionally, the Drosophila guarani species group has been divided into two subgroups: the guarani and the guaramunu subgroups. Two, out of the four species included in this research, are members of the guarani subgroup (D. ornatifrons Duda, 1927 and D. subbadia Paterson & Mainland, 1943) and two are included in the guaramunu subgroup (D. maculifrons Duda, 1927 and D. griseolineata Duda, 1927). However, some authors have suggested that D. maculifrons and D. griseolineata are much closer to some species of the Drosophila tripunctata group than to some of the species of the guarani group. To add new data to the matter under dispute, Polyacrylamide Gel Eletrophoresis (PAGE-SDS) was used for the analysis and comparison of protein composition and Random Amplified Polymorphic DNA (RAPD) analysis to find differences in genomic DNA, in addition to the analysis of quantitative morphological characters previously described. Analysis of PAGE-SDS results in a dendrogram that pointed out D. subbadia as being the most distant within the Drosophila guarani group. However, these results were not supported either by RAPD analysis or by the analysis of continuous morphological characters, which supplied the clustering of D. subbadia with D. ornatifrons. Although our data give strong support to the clustering of D. subbadia and D. ornatifrons, none of the dendrograms provided a clade comprising D. maculifrons and D. griseolineata. Thus, this research does not support the traditional subdivision of the D. guarani group into those two subgroups.

Relationships between host plant architecture and gall abundance and survival

The plant architecture hypothesis predicts that variation in host plant architecture influences insect herbivore community structure, dynamics and performance. In this study we evaluated the effects of Macairea radula (Melastomataceae) architecture on the abundance of galls induced by a moth (Lepidoptera: Gelechiidae). Plant architecture and gall abundance were directly recorded on 58 arbitrarily chosen M. radula host plants in the rainy season of 2006 in an area of Cerrado vegetation, southeastern Brazil. Plant height, dry biomass, number of branches, number of shoots and leaf abundance were used as predicting variables of gall abundance and larval survival. Gall abundance correlated positively with host plant biomass and branch number. Otherwise, no correlation (p > 0.05) was found between gall abundance with shoot number or with the number of leaves/plant. From a total of 124 galls analyzed, 67.7% survived, 14.5% were attacked by parasitoids, while 17.7% died due to unknown causes. Larvae that survived or were parasitized were not influenced by architectural complexity of the host plant. Our results partially corroborate the plant architecture hypothesis, but since parasitism was not related to plant architecture it is argued that bottom-up effects may be more important than top-down effects in controlling the population dynamics of the galling lepidopteran. Because galling insects often decrease plant fitness, the potential of galling insects in selecting for less architectural complex plants is discussed.

Concepts in plant disease resistance

Resistance to nearly all pathogens occurs abundantly in our crops. Much of the resistance exploited by breeders is of the major gene type. Polygenic resistance, although used much less, is even more abundantly available. Many types of resistance are highly elusive, the pathogen apparently adapting very easily them. Other types of resistance, the so-called durable resistance, remain effective much longer. The elusive resistance is invariably of the monogenic type and usually of the hypersensitive type directed against specialised pathogens. Race-specificity is not the cause of elusive resistance but the consequence of it. Understanding acquired resistance may open interesting approaches to control pathogens. This is even truer for molecular techniques, which already represent an enourmously wide range of possibilities. Resistance obtained through transformation is often of the quantitative type and may be durable in most cases.

Silicon in plant disease control

All essential nutrients can affect the incidence and severity of plant diseases. Although silicon (Si) is not considered as an essential nutrient for plants, it stands out for its potential to decrease disease intensity in many crops. The mechanism of Si action in plant resistance is still unclear. Si deposition in plant cell walls raised the hypothesis of a possible physical barrier to pathogen penetration. However, the increased activity of phenolic compounds, polyphenol oxidases and peroxidases in plants treated with Si demonstrates the involvement of this element in the induction of plant defense responses. The studies examined in this review address the role of Si in disease control and the possible mechanisms involved in the mode of Si action in disease resistance in plants.