Aluminum rapidly depolymerizes cortical microtubules and depolarizes the plasma membrane: evidence that these responses are mediated by a glutamate receptor

Efforts to understand how plants respond to aluminum have focused on describing the symptoms of toxicity and elucidating mechanisms of tolerance; however, little is known about the signal transduction steps that initiate the plant's response. Here, we image cortical microtubules and quantify plasma-membrane potential in living, root cells of intact Arabidopsis seedlings. We show that aluminum depolymerizes microtubules and depolarizes the membrane, and that these responses are prevented by calcium channel blockade. Calcium influx might involve glutamate receptors, which in animals are ligand-gated cation channels and are present in the Arabidopsis genome. We show that glutamate depolymerizes microtubules and depolarizes the plasma membrane. These responses, and also the inhibition of root elongation, occur within the first few min of treatment, but are evoked more rapidly by glutamate than by aluminum. Microtubule depolymerization and membrane depolarization, induced by either glutamate or aluminum, are blocked by a specific antagonist of ionotropic glutamate receptors, 2-amino-5-phosphonopentanoate; whereas an antagonist of an aluminum-gated anion channel blocks the two responses to aluminum but not to glutamate. For growth, microtubule integrity, and membrane potential, responses to combined glutamate and aluminum were not greater than to glutamate alone. We propose that signaling in response to aluminum is initiated by efflux of a glutamate-like ligand through an anion channel and the binding of this ligand to a glutamate receptor.     

Vascular leak syndrome of Sprague-Dawley rats in a mandibular distraction osteogenesis study

Vascular leak syndrome (VLS) is a common and often fatal sequela of multiple bone traumas, and of infectious, toxic, and allergic insults in human patients. Although an animal model for VLS has not been fully established, rats have shown sensitivity to the syndrome that approximates that of the human population. We describe cases of VLS in three-month-old adult and one-month-old Sprague-Dawley rats in an osteogenesis study aimed at optimizing correction of bone hypoplasias and other craniofacial deformities in children, using a mandibular distraction device. In the study reported here, VLS was diagnosed in 40% of the rats that were necropsied after dying or being euthanized early, subsequent to mandibular osteotomy, a procedure that involves minimal bone trauma. The gross and histologic findings, as well as the clinical course of VLS in the rats of the osteogenesis study, were similar to those of documented human cases. Hence, the rat may be a useful animal model to h elp characterize the physiologic and molecular events that accompany this syndrome.     

Interactions between Mycobacterium leprae and simian immunodeficiency virus (SIV) in rhesus monkeys

Groups of rhesus monkeys were inoculated with: 1) simian immunodeficiency virus (SIV)B670 alone; 2) Mycobacterium leprae alone; 3) SIV plus M. leprae on the same day; and 4) M. leprae 2 weeks after SIV. Animals were monitored at intervals for virus loads, antibody responses to M. leprae glycolipid antigens and to SIV Gp120, T-cell CD4+ and CD4+ CD29+ subset percentages, leprosy and acquired immunodeficiency syndrome (AIDS) clinical symptoms. Five out of six animals developed leprosy in each co-inoculated group, compared to one out of six in the M. leprae-only-inoculated group, indicating that M. leprae/SIV co-infection increases the susceptibility to leprosy, regardless of the timing of the two infections. Animals in the co-infected group that received M. leprae 2 weeks after SIV had a significantly slower rate of AIDS progression and long-term survival was significantly greater (three out of six) compared to the group inoculated with SIV alone (zero out of seven). All M. leprae-only-inoculated animals (six out of six) survived. Post-SIV-inoculation, a rapid decrease in the percentages of CD4 + and CD4 + CD29 + T-cells was observed in the SIV-only-inoculated group that was significantly blocked by co-inoculation with M. leprae 2 weeks after SIV, but not by SIV on the same day. The virus load set point was increased by approximately two logs in the group inoculated with M. leprae and SIV on the same day compared to SIV 2 weeks prior to M. leprae or the SIV-only-inoculated group. The results indicate that M. leprae, inoculated 2 weeks after SIV, decreased the pathogenicity of SIV compared to inoculation of M. leprae and SIV on the same day or SIV alone. The decreased pathogenicity correlated with a diminished loss of CD4 + and CD4 + CD29 + T-cell subsets in the group inoculated with M. leprae 2 weeks after SIV compared to the group inoculated with SIV alone. IgG antibody responses to M. leprae-specific cell wall phenolic glycolipid-I antigen were inhibited by 2-week-prior or same-day SIV co-inoculation compared to M. leprae-only inoculated animals. The IgG anti-lipoarabinomannan antibody response was enhanced in the group inoculated with M. leprae and SIV on the same day compared to the groups inoculated with M. leprae alone or SIV 2 weeks prior to M. leprae. Antibody responses to SIV Gp120 antigen were unimpaired in both co-inoculated groups compared to SIV-only-inoculated groups. The antibody results show that the immune responses to SIV and M. leprae are interrelated in SIV/M. leprae co-infected animals.     

The Arabidopsis thaliana PPX/PP4 phosphatases: molecular cloning and structural organization of the genes and immunolocalization of the proteins to plastids

The PPX/PP4 Ser/Thr protein phosphatases belong to the type 2A phosphatase subfamily and are present in most eukaryotic organisms. We have previously isolated two closely related DNAs encoding PPX isoforms (PPX-1 and PPX-2) of Arabidopsis thaliana. Here we report the molecular cloning of the genes encoding these proteins. The genes PPX-1 and PPX-2 are composed of eight exons and seven introns located at equivalent positions related to the coding sequences. Whereas the intron-exon organization of the PPX genes is completely different from that of the PP2A-3/PP2A-4 A. thaliana family, specific intron-exon boundaries are conserved among PPX genes from distantly related organisms. Based on GUS expression, both PPX genes show the same spatial and temporal pattern of expression: they are expressed in all the organs and tissues analyzed, and from the earliest stage of development. When PPX proteins were localized to the root in semi-thin methacrylate sections by immunofluorescence, staining was predominantly confined to small organelles, shown to be plastids by co-localization of PPX and ferredoxin. Interestingly, only some ferredoxin-positive plastids were also PPX-positive, and PPX staining was consistently brighter in the epidermis. The localization was confirmed with immunogold and electron microscopy. Our results suggest that, despite its strong sequence conservation, PPX in plants functions differently than in animals.     

Analysis of Cell Division and Elongation Underlying the Developmental Acceleration of Root Growth in Arabidopsis thaliana

To investigate the relation between cell division and expansion in the regulation of organ growth rate, we used Arabidopsis thaliana primary roots grown vertically at 20°C with an elongation rate that increased steadily during the first 14 d after germination. We measured spatial profiles of longitudinal velocity and cell length and calculated parameters of cell expansion and division, including rates of local cell production (cells mm⁻¹ h⁻¹) and cell division (cells cell⁻¹ h⁻¹). Data were obtained for the root cortex and also for the two types of epidermal cell, trichoblasts and atrichoblasts. Accelerating root elongation was caused by an increasingly longer growth zone, while maximal strain rates remained unchanged. The enlargement of the growth zone and, hence, the accelerating root elongation rate, were accompanied by a nearly proportionally increased cell production. This increased production was caused by increasingly numerous dividing cells, whereas their rates of division remained approximately constant. Additionally, the spatial profile of cell division rate was essentially constant. The meristem was longer than generally assumed, extending well into the region where cells elongated rapidly. In the two epidermal cell types, meristem length and cell division rate were both very similar to that of cortical cells, and differences in cell length between the two epidermal cell types originated at the apex of the meristem. These results highlight the importance of controlling the number of dividing cells, both to generate tissues with different cell lengths and to regulate the rate of organ enlargement.     

GERMINATION ECOPHYSIOLOGY OF HYDROPHYLLUM APPENDICULATUM,A MESIC FOREST BIENNIAL

In north central Kentucky, seeds of the mesic forest biennial Hydrophyllum appendiculatum Michx., are innately dormant at maturity in June. Under natural and simulated seasonal temperature changes, dormancy break occurred in two stages. Root dormancy was broken by high summer temperatures, and shoot dormancy was broken by low winter temperatures. Consequently, roots emerged from seeds during autumn, and cotyledons emerged the following spring. A 90-day warm (30/15 C) stratification treatment broke root dormancy, but the roots emerged only after transfer to lower temperatures. After the warm stratification treatment, roots emerged from 93, 73, 6 and 9% of the seeds incubated at 5, 15/6, 20/10 and 30/15 C (12/12 hr), respectively. Zero, 28, 56 and 84 days of cold (5 C) stratification of seeds with emerged roots resulted in 9, 21, 49 and 82% cotyledon emergence, respectively, at 20/10 C. Thus, H. appendiculatum exhibits a type of morpho-physiological dormancy known as epicotyl dormancy. Although many seeds germinate the first year, others remain dormant and germinate in successive years until the fourth season after ripening.     

Fruit and seed heteromorphism in the cold desert annual ephemeral Diptychocarpus strictus (Brassicaceae) and possible adaptive significance

Background and Aims

Diptychocarpus strictus is an annual ephemeral in the cold desert of northwest China that produces heteromorphic fruits and seeds. The primary aims of this study were to characterize the morphology and anatomy of fruits and seeds of this species and compare the role of fruit and seed hetermorphism in dispersal and germination.

Methods

Shape, size, mass and dispersal of siliques and seeds and the thickness of the mucilage layer on seeds were measured, and the anatomy of siliques and seeds, the role of seed mucilage in water absorption/dehydration, germination and adherence of seeds to soil particles, the role of pericarp of lower siliques in seed dormancy and seed after-ripening and germination phenology were studied using standard procedures.

Key Results

Plants produce dehiscent upper siliques with a thin pericarp containing seeds with large wings and a thick mucilage layer and indehiscent lower siliques with a thick pericarp containing nearly wingless seeds with a thin mucilage layer. The dispersal ability of seeds from the upper siliques was much greater than that of intact lower siliques. Mucilage increased the amount of water absorbed by seeds and decreased the rate of dehydration. Seeds with a thick mucilage layer adhered to soil particles much better than those with a thin mucilage layer or those from which mucilage had been removed. Fresh seeds were physiologically dormant and after-ripened during summer. Non-dormant seeds germinated to high percentages in light and in darkness. Germination of seeds from upper siliques is delayed until spring primarily by drought in summer and autumn, whereas the thick, indehiscent pericarp prevents germination for >1 year of seeds retained in lower siliques.

Conclusions

The life cycle of D. strictus is morphologically and physiologically adapted to the cold desert environment in time and space via a combination of characters associated with fruit and seed heteromorphism.     

A new type of specialized morphophysiological dormancy and seed storage behaviour in Hydatellaceae, an early-divergent angiosperm family

Background and Aims

Recent phylogenetic analysis has placed the aquatic family Hydatellaceae as an early-divergent angiosperm. Understanding seed dormancy, germination and desiccation tolerance of Hydatellaceae will facilitate ex situ conservation and advance hypotheses regarding angiosperm evolution.

Methods

Seed germination experiments were completed on three species of south-west Australian Hydatellaceae, Trithuria austinensis, T. bibracteata and T. submersa, to test the effects of temperature, light, germination stimulant and storage. Seeds were sectioned to examine embryo growth during germination in T. austinensis and T. submersa.

Key Results

Some embryo growth and cell division in T. austinensis and T. submersa occurred prior to the emergence of an undifferentiated embryo from the seed coat (‘germination’). Embryo differentiation occurred later, following further growth and a 3- to 4-fold increase in the number of cells. The time taken to achieve 50 % of maximum germination for seeds on water agar was 50, 35 and 37 d for T. austinensis, T bibracteata and T. submersa, respectively.

Conclusions

Seeds of Hydatellaceae have a new kind of specialized morphophysiological dormancy in which neither root nor shoot differentiates until after the embryo emerges from the seed coat. Seed biology is discussed in relation to early angiosperm evolution, together with ex situ conservation of this phylogenetically significant group.     

How can malaria rapid diagnostic tests achieve their potential? A qualitative study of a trial at health facilities in Ghana

Malaria is still a major public health problem in Brazil, with approximately 306 000 registered cases in 2009, but it is estimated that in the early 1940s, around six million cases of malaria occurred each year. As a result of the fight against the disease, the number of malaria cases decreased over the years and the smallest numbers of cases to-date were recorded in the 1960s. From the mid-1960s onwards, Brazil underwent a rapid and disorganized settlement process in the Amazon and this migratory movement led to a progressive increase in the number of reported cases. Although the main mosquito vector (Anopheles darlingi) is present in about 80% of the country, currently the incidence of malaria in Brazil is almost exclusively (99,8% of the cases) restricted to the region of the Amazon Basin, where a number of combined factors favors disease transmission and impair the use of standard control procedures. Plasmodium vivax accounts for 83,7% of registered cases, while Plasmodium falciparum is responsible for 16,3% and Plasmodium malariae is seldom observed. Although vivax malaria is thought to cause little mortality, compared to falciparum malaria, it accounts for much of the morbidity and for huge burdens on the prosperity of endemic communities. However, in the last few years a pattern of unusual clinical complications with fatal cases associated with P. vivax have been reported in Brazil and this is a matter of concern for Brazilian malariologists. In addition, the emergence of P. vivax strains resistant to chloroquine in some reports needs to be further investigated. In contrast, asymptomatic infection by P. falciparum and P. vivax has been detected in epidemiological studies in the states of Rondonia and Amazonas, indicating probably a pattern of clinical immunity in both autochthonous and migrant populations. Seropidemiological studies investigating the type of immune responses elicited in naturally-exposed populations to several malaria vaccine candidates in Brazilian populations have also been providing important information on whether immune responses specific to these antigens are generated in natural infections and their immunogenic potential as vaccine candidates. The present difficulties in reducing economic and social risk factors that determine the incidence of malaria in the Amazon Region render impracticable its elimination in the region. As a result, a malaria-integrated control effort - as a joint action on the part of the government and the population - directed towards the elimination or reduction of the risks of death or illness, is the direction adopted by the Brazilian government in the fight against the disease.     

Mapping of citrullinated fibrinogen B-cell epitopes in rheumatoid arthritis by imaging surface plasmon resonance

Introduction  

Rheumatoid arthritis (RA) frequently involves the loss of tolerance to citrullinated antigens, which may play a role in pathogenicity. Citrullinated fibrinogen is commonly found in inflamed synovial tissue and is a frequent target of autoantibodies in RA patients. To obtain insight into the B-cell response to citrullinated fibrinogen in RA, its autoepitopes were systematically mapped using a new methodology.