Pollination in Geonoma macrostachys and Three Congeners,G. acaulis,G. gracilis,and G. interrupta

A continuous 15 month study of the floral ecology of four syntopic understorey palm species of Genoma was conducted in Amazonian Peru lowland rainforest. The spicate inflorescences of G. macrostachys, G. acaulis and G. gracilis are strictly protandrous and the plants are functionally dioecious. Data suggest that in G. macrostachys and G. acaulis pollination is based on a mimicry system, the pistillate flowers mimicking the staminate ones in colour, shape and scent. Pollen-collecting meliponine bees (Hymenoptera, Apidae, Meliponinae) and pollen-feeding syrphid flies (Diptera, Syrphidae) which visit inflorescences during both sexual stages are the pollinators of G. macrostachys. Geonoma acaulis is pollinated by small pollen-feeding weevils (Coleoptera, Curculionidae, Derelomini) that visit male and female spikes. Additionally, in G. macrostachys another pollinator type, viz. euglossine bees (Hymenoptera, Apidae, Euglossinae), which are attracted and rewarded by both types of flowers may account for long-distance pollination. The palm G. gracilis shows a very distinct pollination system. Although opportunistic insect visitors are attracted to the inflorescences of this species it seems to be mainly anemophilous because pollen becomes powdery during an thesis. The branched inflorescences of G. interrupta are also protandrous, but unlike the other species of Geonoma observed, staminate and pistillate anthesis of individual flowers are, for the most, overlapping. A broad spectrum of visitors is attracted (bees, wasps, flies, and beetles), which all may act as pollinators. Outcrossing is especially encouraged during the purely female phase at the end of the flowering cycle when there are no more staminate flowers in the inflorescence. Effects on the reproductive biology and population structure of different pollination systems and breeding system are discussed.     

Two G12 family G proteins, G alpha12 and G alpha13, show different subcellular localization

The G alpha subunits of the G12 family of heterotrimeric G proteins, G alpha12 and G alpha13, are closely related in sequences and some effectors, but they often act through different pathways or bind to different proteins. We have examined subcellular distribution of these two G proteins and found that endogenous G alpha12 and G alpha13 localize in membrane and cytoplasmic fractions, respectively. Exogenously expressed G alpha12 and G alpha13 also localize in membrane and cytoplasmic fractions, respectively, in COS-7 cells. Stimulation of lysophosphatidic acid receptor coupled to G alpha13 markedly promotes the translocation of G alpha13 from cytoplasm to membrane. This different localization of G alpha12 and G alpha13 may explain some of the nonoverlapping actions of G alpha12 and G alpha13.     

A new method to discriminate G1, S, G2, M, and G1 postmitotic cells

A new flow cytometric method combining light scattering measurements, detection of bromodeoxyuridine (BrdU) incorporation via fluorescent antibody, and quantitation of cellular DNA content by propidium iodide (PI) allows identification of additional compartments in the cell cycle. Thus, while cell staining with BrdU-antibodies and PI reveals the G1, S, and G2 + M phases of the cell cycle, differences in light scattering allow separation of G2 phase cells from M phase cells and subdivision of G1 phase into two compartments, i.e., G1A representing postmitotic cells which mature to G1B cells ready to initiate DNA synthesis. The method involves fixation of cells in 70% ethanol, extraction of histones with HC1, and thermal denaturation of DNA. This treatment appears to enhance the differences in chromatin structure of cells in the various phases of the cell cycle to the extent that cells could be separated on the basis of the 90 degrees scatter. Mitotic cells show much lower scatter than G2 phase cells, and G1 postmitotic cells (G1A) show lower scatter than G1 cells about to enter the S phase (G1B). Light scattering is correlated with chromatin condensation, as judged by microscopic evaluation of cells sorted on the basis of light scatter. The method has the advantage over the parental BrdU/DNA bivariate analysis in allowing the G2 and M phases of the cell cycle to be separated and the G1 phase to be analyzed in more detail. The method may also allow separation of unlabeled S phase cells from mitotic cells and distinguish between labeled and unlabeled mitotic cells.     

Big G,little G: G proteins and actin cytoskeletal reorganization

It has been known for some time that stimulation of heterotrimeric G protein-coupled receptors can cause cytoskeletal reorganization. A recent report in Developmental Cell demonstrates that the activation of a tyrosine kinase, C-terminal Src kinase, by heterotrimeric G protein subunits provides the trigger for Rho-dependent actin stress fiber formation.     

Molecular Characterization of Echinococcus granulosus Cysts in North Indian Patients: Identification of G1, G3, G5 and G6 Genotypes

Background

Cystic echinococcosis (CE) caused by the Echinococcus granulosus, is a major public health problem worldwide, including India. The different genotypes of E. granulosus responsible for human hydatidosis have been reported from endemic areas throughout the world. However, the genetic characterization of E. granulosus infecting the human population in India is lacking. The aim of study was to ascertain the genotype(s) of the parasite responsible for human hydatidosis in North India.

Methodology/Principal Findings

To study the transmission patterns of E. granulosus, genotypic analysis was performed on hydatid cysts obtained from 32 cystic echinococcosis (CE) patients residing in 7 different states of North India. Mitochondrial cytochrome c oxidase subunit1 (cox1) sequencing was done for molecular identification of the isolates. Most of the CE patients (30/32) were found to be infected with hydatid cyst of either G3 (53.1%) or G1 (40.62%) genotype and one each of G5 (cattle strain) and G6 (camel strain) genotype.

Conclusions/Significance

These findings demonstrate the zoonotic potential of G1 (sheep strain) and G3 (buffalo strain) genotypes of E. granulosus as these emerged as predominant genotypes infecting the humans in India. In addition to this, the present study reports the first human CE case infected with G5 genotype (cattle strain) in an Asian country and presence of G6 genotype (camel strain) in India. The results may have important implications in the planning of control strategies for human hydatidosis.     

N G,N G -Dimethyl-l-arginine,a dominant precursor of endogenous dimethylamine in rats

Summary The metabolic significance ofN ^G ,N ^G -dimethyl-l-arginine (DMA) as a precursor of endogenous dimethylamine (DMN) in rats was examined in connection with the wide distribution and active operation of dimethylargininase (EC3.5.3.18) in rat tissues (Kimoto et al., 1993). When [methyl-¹⁴C]DMA was administered intraperitoneally to rats, the radioactive DMN was detected in various tissues as a major radioactive metabolite one hour after injection, and about 65% of the radioactivity administered was recovered in the first 12-h urine as DMN. In the case of the [¹⁴C] DMN-injected rats, almost all the radioactivity was excreted in the 12-h urine as DMN, except for a negligible amount of radioactivity found in urea. The time-dependent decrease in the specific radioactivity of DMA and DMN in urine showed that dimethylargininase was significantly involved in thein vivo formation of DMN by the hydrolytic cleavage of DMA released from methylated proteins and that DMA is a dominant precursor of endogenous DMN in rats.     

Micropropagation of four Gentiana species (G. lutea, G. cruciata, G. purpurea and G. acaulis)

The growth of axillary shoots was initiated on nodal stem segments, excised from aseptically grown seedlings of Gentiana acaulis L., G. cruciata L., G. lutea L. and G. purpurea L. In later subcultures, a basal callus tissue developed on the shoots, giving rise to de novo formed buds. Optimum benzyladenine and indoleacetic acid combinations for shoot development were established. They were slightly different in the four species. From 35-70% of shoots rooted spontaneously, except in G. lutea, in which adventitious roots were induced by applying naphthaleneacetic acid. It was conduded that the four Gentiana species were amenable to propagation in vitro. This revised version was published online in June 2006 with corrections to the Cover Date.     

The comparative leaf anatomy of Goniothamus andersonii, G. macrophyllus, G. malayanus and G. velutinus

The leaf anatomy of Goniothalamus andersonii, G. macrophyllus, G. malayanus and G. velutinus from the peat swamps of Sarawak is compared. Sufficient anatomical differences exist to differentiate the four species. G. velutinus has many points of difference from the other three species and G. macrophyllus is readily identified by the presence of fibre-sclereids in the lamina mesophyll. G. andersonii and G. malayanus are similar to each other, but G. andersonii can be distinguished, in particular by the more pronounced multiple projections of the outer periclinal walls of the epidermal cells and the presence of thick and cutinised outer ends of the anticlinal walls of the epidermal cells.     

Small, monomeric G proteins in plants

The superfamily of small, monomeric GTP-binding proteins, in Arabidopsis thaliana comprising 93 members, is classified into four families: Arf/Sar, Rab, Rop/Rac, and Ran families. All monomeric G proteins function as molecular switches that are activated by GTP and inactivated by the hydrolysis of GTP to GDP. GTP/GDP cycling is controlled by three classes of regulatory protein: guanine-nucleotide-exchange factors (GEFs), GTPase-activating proteins (GAPs), and guanine-nucleotide-dissociation inhibitors (GDIs). Proteins of Arf family are primarily involved in regulation of membrane traffic and organization of the cytoskeleton. Arf1/Sar1 proteins regulate the formation of vesicle coat at different steps in the exocytic and endocytic pathways. Rab GTPases are regulators of vesicular transport. They are involved in vesicle formation, recruitment of cytoskeletal motor proteins, and in vesicle tethering and fusion. Rop proteins serve as key regulators of cytoskeletal reorganization in response to extracellular signals. Several data have also shown that Rop proteins play additional roles in membrane trafficking and regulation of enzymes activity. Ran proteins are involved in nucleocytoplasmic transport.     

G12/G13 family G proteins regulate marginal zone B cell maturation, migration, and polarization

G protein-coupled receptors play an important role in the regulation of lymphocyte functions such as migration, adhesion, proliferation, and differentiation. Although the role of G(i) family G proteins has been intensively studied, no in vivo data exist with respect to G12/G13 family G proteins. We show in this study that mice that lack the G protein alpha-subunits G alpha12 and G alpha13 selectively in B cells show significantly reduced numbers of splenic marginal zone B (MZB) cells, resulting in a delay of Ab production in response to thymus-independent Ags. Basal and chemokine-induced adhesion to ICAM-1 and VCAM-1, two adhesion molecules critically involved in MZB localization, is normal in mutant B cells, and the same is true for chemokine-induced migration. However, migration in response to serum and sphingosine 1-phosphate is strongly increased in mutant MZB cells, but not in mutant follicular B cells. Live-cell imaging studies revealed that G alpha12/G alpha13-deficient MZB cells assumed more frequently an ameboid form than wild-type cells, and pseudopod formation was enhanced. In addition to their regulatory role in serum- and sphingosine 1-phosphate-induced migration, G12/G13 family G proteins seem to be involved in peripheral MZB cell maturation, because also splenic MZB cell precursors are reduced in mutant mice, although less prominently than mature MZB cells. These data suggest that G12/G13 family G proteins contribute to the formation of the mature MZB cell compartment both by controlling MZB cell migration and by regulating MZB cell precursor maturation.     

Biosynthetic relationship among aflatoxins B1, B2, G1, and G2

Aspergillus parasiticus NIAH-26, a UV-irradiated mutant of A. parasiticus SYS-4 (NRRL 2999), produces neither aflatoxins nor precursors. When sterigmatocystin (ST) or O-methylsterigmatocystin was fed to this mutant in YES medium, aflatoxins B1 (AFB1) and G1 (AFG1) were produced. When dihydrosterigmatocystin (DHST) or dihydro-O-methylsterigmatocystin was fed to this mold, aflatoxins B2 (AFB2) and G2 (AFG2) were produced. The reactions from ST to AFB1 and DHST to AFB2 were also observed in the cell-free system and were catalyzed stepwise by the methyltransferase and oxidoreductase enzymes. In the feeding experiments of strain NIAH-26, the convertibility from ST to AFB1-AFG1 was found to be remarkably suppressed by the coexistence of DHST in the medium, and the convertibility from DHST to AFB2-AFG2 was also suppressed by the presence of ST. When some other mutants which endogenously produce a small amount of aflatoxins (mainly AFB1 and AFG1) were cultured with DHST, the amounts of AFB1 and AFG1 produced were significantly decreased, whereas AFB2 and AFG2 were newly produced. In similar feeding experiments in which 27 kinds of mutants including these mutants were used, most of the mutants which were able to convert exogenous ST to AFB1-AFG1 were also found to convert exogenous DHST to AFB2-AFG2. These results suggest that the same enzymes may be involved in the both biosynthetic pathways from ST to AFB1-AFG1 and DHST to AFB2-AFG2. The reactions described herein were not observed when the molds had been cultured in the YEP medium.     

Biosynthetic relationship among aflatoxins B1, B2, G1, and G2.

Aspergillus parasiticus NIAH-26, a UV-irradiated mutant of A. parasiticus SYS-4 (NRRL 2999), produces neither aflatoxins nor precursors. When sterigmatocystin (ST) or O-methylsterigmatocystin was fed to this mutant in YES medium, aflatoxins B1 (AFB1) and G1 (AFG1) were produced. When dihydrosterigmatocystin (DHST) or dihydro-O-methylsterigmatocystin was fed to this mold, aflatoxins B2 (AFB2) and G2 (AFG2) were produced. The reactions from ST to AFB1 and DHST to AFB2 were also observed in the cell-free system and were catalyzed stepwise by the methyltransferase and oxidoreductase enzymes. In the feeding experiments of strain NIAH-26, the convertibility from ST to AFB1-AFG1 was found to be remarkably suppressed by the coexistence of DHST in the medium, and the convertibility from DHST to AFB2-AFG2 was also suppressed by the presence of ST. When some other mutants which endogenously produce a small amount of aflatoxins (mainly AFB1 and AFG1) were cultured with DHST, the amounts of AFB1 and AFG1 produced were significantly decreased, whereas AFB2 and AFG2 were newly produced. In similar feeding experiments in which 27 kinds of mutants including these mutants were used, most of the mutants which were able to convert exogenous ST to AFB1-AFG1 were also found to convert exogenous DHST to AFB2-AFG2. These results suggest that the same enzymes may be involved in the both biosynthetic pathways from ST to AFB1-AFG1 and DHST to AFB2-AFG2. The reactions described herein were not observed when the molds had been cultured in the YEP medium.     

A dimeric RNA quadruplex architecture comprised of two G:G(:A):G:G(:A) hexads,G:G:G:G tetrads and UUUU loops

Using CD and NMR, we determined the structure of an RNA oligomer, r(GGAGGUUUUGGAGG) (R14), comprising two GGAGG segments joined by a UUUU segment. A modified quadruplex structure was observed for r(GGAGGUUUUGGAGG) in solution even in the absence of K(+). An unusually stable dimeric RNA quadruplex architecture formed from two strands of r(GGAGGUUUUGGAGG) at low K(+) concentration is reported here. In each strand of r(GGAGGUUUUGGAGG), two sets of successive turns in the GGAGG segments and turns at both ends of the UUUU loops drive four G-G steps to align in a parallel manner, a core with two stacked G-tetrads being formed. Two adenine bases bind to two edges of one G:G:G:G tetrad through the sheared G:A mismatch augmenting the tetrad into a G:G(:A):G:G(:A) hexad. Thus, one molecule of r(GGAGGUUUUGGAGG) folds into a modified quadruplex comprising a G:G:G:G tetrad, a UUUU double-chain reversal loop and a G:G(:A):G:G(:A) hexad. Two such molecules further associate by stacking through the dimeric hexad-hexad interface with a rotational symmetry. The ribose rings of most nucleotides take S (close to C2'-endo) puckering, which is unusual for an RNA. K(+) can increase the stability of this quadruplex structure; the number of bound K(+) was estimated from the results of the titration experiment. Besides G:G and G:A mismatches, a network of hydrogen bonds including O4'-NH(2) and C-H..O hydrogen bonds, and the extensive base stacking contribute to the high thermodynamic stability of R14. Our results could provide the stereochemical and thermodynamic basis for elucidating the biological role of the GGAGG-containing RNA segments abundantly existing in various RNAs. Relevance to quadruplex-mediated mRNA-FMRP binding and HIV-1 genome RNA dimerization is discussed.     

Sulfhydryl groups during the S phase: comparison of cells from G 1 , plateau-phase G 1 , and G 0

The non-protein sulfhydryl (NPSH) content of cells moving into S from G₁, plateau phase G₁, and G₀ was measured. Chinese hamster ovary (CHO) cells accumulated in G₁ by growth into plateau phase contain only one-fourth the NPSH concentration of cycling C₁ cells or G₁ cells accumulated by brief growth in isoleucine-deficient medium. Upon dilution of plateau cultures with fresh medium, cellular NPSH content increases rapidly, reaching the same level as that in cycling cells within four hours. This increase is prevented by cycloheximide but not by actinomycin D or hydroxyurea. Neither CHO cells cycling in vitro nor salivary gland G₀ cells stimulated with isoproterenol in vivo show significant changes in intracellular NPSH concentrations during S phase. This suggests that the concentration of intracellular NPSH (glutathione) remains constant during the cell cycle except when cells are grown to plateau phase in exhausted or deficient medium, in which case normal degradation exceeds synthesis and the gross level falls until fresh medium is provided and synthesis, apparently on preexisting RNA templates, accelerates.