Medicago truncatula contains a second gene encoding a plastid located glutamine synthetase exclusively expressed in developing seeds

<p>Abstract</p> <p>Background</p> <p>Nitrogen is a crucial nutrient that is both essential and rate limiting for plant growth and seed production. Glutamine synthetase (GS), occupies a central position in nitrogen assimilation and recycling, justifying the extensive number of studies that have been dedicated to this enzyme from several plant sources. All plants species studied to date have been reported as containing a single, nuclear gene encoding a plastid located GS isoenzyme per haploid genome. This study reports the existence of a second nuclear gene encoding a plastid located GS in <it>Medicago truncatula</it>.</p> <p>Results</p> <p>This study characterizes a new, second gene encoding a plastid located glutamine synthetase (GS2) in <it>M. truncatula</it>. The gene encodes a functional GS isoenzyme with unique kinetic properties, which is exclusively expressed in developing seeds. Based on molecular data and the assumption of a molecular clock, it is estimated that the gene arose from a duplication event that occurred about 10 My ago, after legume speciation and that duplicated sequences are also present in closely related species of the Vicioide subclade. Expression analysis by RT-PCR and western blot indicate that the gene is exclusively expressed in developing seeds and its expression is related to seed filling, suggesting a specific function of the enzyme associated to legume seed metabolism. Interestingly, the gene was found to be subjected to alternative splicing over the first intron, leading to the formation of two transcripts with similar open reading frames but varying 5' UTR lengths, due to retention of the first intron. To our knowledge, this is the first report of alternative splicing on a plant GS gene.</p> <p>Conclusions</p> <p>This study shows that <it>Medicago truncatula </it>contains an additional GS gene encoding a plastid located isoenzyme, which is functional and exclusively expressed during seed development. Legumes produce protein-rich seeds requiring high amounts of nitrogen, we postulate that this gene duplication represents a functional innovation of plastid located GS related to storage protein accumulation exclusive to legume seed metabolism.</p

Water beetles (Coleoptera) of small reservoirs in the neighborhood of Swinoujscie (NW Poland)

The present paper describes a diversity of water beetle communities inhabiting five small water reservoirs, located in the north-western part of Wolin Island, near of Świnoujście city (Poland). The analyzed aspects of beetle communities included differences in species composition and the abundance of beetles in various water bodies, taking into account such features of the reservoirs as their size, periodical character, maximum depth, structure of vegetation and the percentage of surface shaded by plant canopy. In total, 60 species of beetles were recorded in the reservoirs, including three species endangered with extinction in Poland, i.e. Haliplus apicalis , H. furcatus , H. variegatus, and one species critically endangered with extinction in Poland, namely Spercheus emarginatus. The largest number of species (42) and individuals (1294) was found in a periodical, relatively big, open and shallow pool situated in a lowland peat bog and covered with soft submerged vegetation. However, the population of beetles found in this location was strongly dominated by two species, Hydrochara caraboides and Hygrotus decoratus, which resulted in the lowest biodiversity coef ficient (H` = 0.705) in comparison with the other investigated reservoirs. In permanent but significantly shaded reservoirs, the number of recorded species was almost two times lower and the abundance of beetles was even eight times lower. However, in such water bodies the diversity coef icient had the highest values (0.981 0.991). As fa As far as the environmental aspects were concerned, it was discovered that the most significant were the size of the reservoir and its permanent/non-permanent character. Only the differences in size reached the level of statistical validity (p = 0.040), explaining 34.8% of cases of species variability. The similarity among beetle communities inhabiting particular reservoirs varied from 31.63% to 53.3% and was connected with ecological similarity of the investigated water bodies

Function of two β−carotenes near the D1 and D2 proteins in photosystem II dimers

The antenna proteins in photosystem II (PSII) not only promote energy transfer to the photosynthetic reaction center (RC) but provide also an efficient cation sink to re-reduce chlorophyll a if the electron transfer (ET) from the Mn-cluster is inhibited. Using the newest PSII dimer crystal structure (3.0 Å resolution), in which 11 β-carotene molecules (Car) and 14 lipids are visible in the PSII monomer, we calculated the redox potentials (Em) of one-electron oxidation for all Car (Em(Car)) by solving the Poisson–Boltzmann equation. In each PSII monomer, the D1 protein harbors a previously unlocated Car (CarD1) in van der Waals contact with the chlorin ring of ChlZ(D1). Each CarD1 in the PSII dimer complex is located in the interface between the D1 and CP47 subunits, together with another four Car of the other PSII monomer and several lipid molecules. The proximity of Car bridging between CarD1 and plastoquinone/QA may imply a direct charge recombination of Car+QA−. The calculated Em(CarD1) and Em(ChlZ(D1)) are, respectively, 83 and 126 mV higher than Em(CarD2) and Em(ChlZ(D2)), which could explain why CarD2+ and ChlZ(D2)+ are observed rather than the corresponding CarD1+ and ChlZ(D1)+

How photosynthetic reaction centers control oxidation power in chlorophyll pairs P680, P700, and P870

At the heart of photosynthetic reaction centers (RCs) are pairs of chlorophyll a (Chla), P700 in photosystem I (PSI) and P680 in photosystem II (PSII) of cyanobacteria, algae, or plants, and a pair of bacteriochlorophyll a (BChla), P870 in purple bacterial RCs (PbRCs). These pairs differ greatly in their redox potentials for one-electron oxidation, E(m). For P680, E(m) is 1,100–1,200 mV, but for P700 and P870, E(m) is only 500 mV. Calculations with the linearized Poisson–Boltzmann equation reproduce these measured E(m) differences successfully. Analyzing the origin for these differences, we found as major factors in PSII the unique Mn(4)Ca cluster (relative to PSI and PbRC), the position of P680 close to the luminal edge of transmembrane α-helix d (relative to PSI), local variations in the cd loop (relative to PbRC), and the intrinsically higher E(m) of Chla compared with BChla (relative to PbRC)