Role of AMT1;1 in NH4+ acquisition in Arabidopsis thaliana

AtAMT1;1 was the founding member of the family of AMT/Rh ammonium transporters and accounts for about one third of the total ammonium absorption in the roots of the model plant Arabidopsis. Recent evidence suggested that at least some AMT/Rh proteins are NH3 gas channels. In order to evaluate the transported form of ammonium in AtAMT1;1, the protein was functionally expressed in Xenopus oocytes. AtAMT1;1 elicited NH4+ and methylammonium (MeA+) inward currents that saturated in a voltage-dependent manner with a half maximal concentration of 2.7 +/- 1.6 microM for NH4+ and 5.0 +/- 0.7 microM for the transport analogue methylammonium. AtAMT1;1 was plasma membrane localized and expressed in the root cortex and epidermis, including root hairs. The AtAMT1;1-GFP fusion construct under control of its endogenous promoter revealed additional localization of the protein in the pericycle, in the leaf epidermis, and in mesophyll cells. The functional data and its localization suggest that AtAMT1;1 participates in concentrative NH4+ acquisition in roots, in long-distance transport to the shoots, and in re-uptake of apoplastic NH4+ that derives from photorespiration in shoots.     

The role of transporters in supplying energy to plant plastids

The energy status of plant cells strongly depends on the energy metabolism in chloroplasts and mitochondria, which are capable of generating ATP either by photosynthetic or oxidative phosphorylation, respectively. Another energy-rich metabolite inside plastids is the glycolytic intermediate phosphoenolpyruvate (PEP). However, chloroplasts and most non-green plastids lack the ability to generate PEP via a complete glycolytic pathway. Hence, PEP import mediated by the plastidic PEP/phosphate translocator or PEP provided by the plastidic enolase are vital for plant growth and development. In contrast to chloroplasts, metabolism in non-green plastids (amyloplasts) of starch-storing tissues strongly depends on both the import of ATP mediated by the plastidic nucleotide transporter NTT and of carbon (glucose 6-phosphate, Glc6P) mediated by the plastidic Glc6P/phosphate translocator (GPT). Both transporters have been shown to co-limit starch biosynthesis in potato plants. In addition, non-photosynthetic plastids as well as chloroplasts during the night rely on the import of energy in the form of ATP via the NTT. During energy starvation such as prolonged darkness, chloroplasts strongly depend on the supply of ATP which can be provided by lipid respiration, a process involving chloroplasts, peroxisomes, and mitochondria and the transport of intermediates, i.e. fatty acids, ATP, citrate, and oxaloacetate across their membranes. The role of transporters involved in the provision of energy-rich metabolites and in pathways supplying plastids with metabolic energy is summarized here.     

No evidence for flooding stress memory in saplings of eight hardwood floodplain forest species

Alluvial floodplain forests became rare in many parts of Europe, due to anthropogenic changes. Therefore, restoration of floodplain forests is important, but a difficult task because of the complex environmental conditions. The zonation of woody species in floodplains is mainly determined by hydrological conditions, not only within one year but also during the previous years. Tolerance to flooding can be regarded as a key factor for the successful establishment. We examined whether a previous flooding showed an increased flooding tolerance of saplings from eight woody floodplain forest species after a recurrent flooding under controlled common garden conditions at the research station Gießen-Leihgestern (Germany). This would indicate a stress memory towards flooding stress. The individuals of the experiment already experienced a partial flooding of three different durations (three, six or nine weeks) or no flooding in the previous year. After nine months of recovery, these fourteen-month-old saplings were again either exposed to a partial flooding of nine weeks or no flooding. We assessed foliar injury and growth in terms of plant height, number of leaves and stem diameter three weeks (short-term recovery) and nine months (medium-term recovery) after flooding. The saplings showed no increased tolerance to a recurrent flooding irrespective of the previous experienced flooding duration. Therefore, no immediate stress memory towards flooding stress could be observed. To recover after flooding seems to be the better option compared to forming a stress memory, which explained that most species showed a decreased foliar injury after medium-term compared to short-term recovery period.

     

Siliques are Red1 from Arabidopsis acts as a bidirectional amino acid transporter that is crucial for the amino acid homeostasis of siliques

Many membrane proteins are involved in the transport of nutrients in plants. While the import of amino acids into plant cells is, in principle, well understood, their export has been insufficiently described. Here, we present the identification and characterization of the membrane protein Siliques Are Red1 (SIAR1) from Arabidopsis (Arabidopsis thaliana) that is able to translocate amino acids bidirectionally into as well as out of the cell. Analyses in yeast and oocytes suggest a SIAR1-mediated export of amino acids. In Arabidopsis, SIAR1 localizes to the plasma membrane and is expressed in the vascular tissue, in the pericycle, in stamen, and in the chalazal seed coat of ovules and developing seeds. Mutant alleles of SIAR1 accumulate anthocyanins as a symptom of reduced amino acid content in the early stages of silique development. Our data demonstrate that the SIAR1-mediated export of amino acids plays an important role in organic nitrogen allocation and particularly in amino acid homeostasis in developing siliques.     

The accuracy of measuring glenohumeral motion with a surface humeral cuff

Conclusions about normal and pathologic shoulder motion are frequently made from studies using skin surface markers, yet accuracy of such sensors representing humeral motion is not well known. Nineteen subjects were investigated with flock of birds electromagnetic sensors attached to transcortical pins placed into the scapula and humerus, and a thermoplastic cuff secured on the arm. Subjects completed two repetitions of raising and lowering the arm in the sagittal, scapular and coronal planes, as well as shoulder internal and external rotation with the elbow at the side and abducted to 90°. Humeral motion was recorded simultaneously from surface and bone fixed sensors. The average magnitude of error was calculated for the surface and bone fixed measurements throughout the range of motion. ANOVA tested for differences across angles of elevation, raising and lowering, and differences in body mass index. For all five motions tested, the plane of elevation rotation average absolute error ranged from 0-2°, while the humeral elevation rotation average error ranged from 0-4°. The axial rotation average absolute error was much greater, ranging from 5° during elevation motions to approaching 30° at maximum excursion of internal/external rotation motions. Average absolute error was greater in subjects with body mass index greater than 25. Surface sensors are an accurate way of measuring humeral elevation rotations and plane of elevation rotations. Conversely, there is a large amount of average error for axial rotations when using a humeral cuff to measure glenohumeral internal/external rotation as the primary motion.     

Identification of protective B cell antigens of Legionella pneumophila

Abs confer protection from secondary infection with Legionella pneumophila, the causative agent of a severe form of pneumonia known as Legionnaires' disease. In this study, we demonstrate that Ab-mediated protection is effective across L. pneumophila serogroups, suggesting that Abs specific for conserved protein Ags are sufficient to mediate this protective effect. We used two independent methods to identify immunogenic L. pneumophila protein Ags, namely, the screening of a λ phage library representing the complete L. pneumophila genome and two-dimensional gel electrophoresis combined with Western blot analysis and protein spot identification by mass spectrometry. A total of 30 novel L. pneumophila B cell Ags were identified, the majority of which are located in or associated with the bacterial membrane, where they are accessible for Abs and, therefore, likely to be relevant for Ab-mediated protection against L. pneumophila. Selected B cell Ags were recombinantly expressed and tested in a vaccination protocol. Mice immunized with either single-protein Ags or an Ag combination showed reduced bacterial titers in bronchoalveolar lavage and lung after L. pneumophila challenge. To determine the clinical relevance of these findings, we tested Legionnaires' disease patient sera for reactivity with the identified L. pneumophila Ags. The recognized Ags were indeed conserved across host species, because Abs specific for all three selected Ags could be detected in patient sera, rendering the identified protein Ags potential vaccine candidates.     

Simultaneous boosting of source and sink capacities doubles tuber starch yield of potato plants

An important goal in biotechnological research is to improve the yield of crop plants. Here, we genetically modified simultaneously source and sink capacities in potato (Solanum tuberosum cv. Desirée) plants to improve starch yield. Source capacity was increased by mesophyll‐specific overexpression of a pyrophosphatase or, alternatively, by antisense expression of the ADP‐glucose pyrophosphorylase in leaves. Both approaches make use of re‐routing photoassimilates to sink organs at the expense of leaf starch accumulation. Simultaneous increase in sink capacity was accomplished by overexpression of two plastidic metabolite translocators, that is, a glucose 6‐phosphate/phosphate translocator and an adenylate translocator in tubers. Employing such a ‘pull’ approach, we have previously shown that potato starch content and yield can be increased when sink strength is elevated. In the current biotechnological approach, we successfully enhanced source and sink capacities by a combination of ‘pull’ and ‘push’ approaches using two different attempts. A doubling in tuber starch yield was achieved. This successful approach might be transferable to other crop plants in the future.     

Ten microsatellite loci for the strawberry poison frog (Oophaga pumilio)

We describe primers and PCR conditions to amplify nine new tetranucleotide loci and one new dinucleotide locus isolated from the strawberry poison frog (Oophaga pumilio). In 21 individuals from Costa Rica, the number of alleles ranged from 4 to 16, observed heterozygosities from 40 to 100%, and polymorphic information content ranged from 0.60 to 0.90 per locus. Evidence for linkage disequilibrium was found only between two loci, but this pattern was not found in other populations tested. All primer pairs cross-amplified in Oophaga vicentei from Panama.