Oriented thick and thin filaments in amoeba proteus

Actin and myosin filaments as a foundation of contractile systems are well established from ameba to man (3). Wolpert et al. (19) isolated by differential centrifugation from Amoeba proteus a motile fraction composed of filaments which moved upon the addition of ATP. Actin filaments are found in amebas (1, 12, 13) which react with vertebrate heavy meromyosin (HMM), forming arrowhead complexes as vertebrate actin (3, 9), and are prominent within the ectoplasmic tube where some of them are attached to the plasmalemma (1, 12). Thick and thin filaments possessing the morphological characteristics of myosin and actin have been obtained from isolated ameba cytoplasm (18, 19). In addition, there are filaments exhibiting ATPase activity in amebas which react with actin (12, 16, 17). However, giant ameba (Chaos-proteus) shapes are difficult to preserve, and the excellent contributions referred to above are limited by visible distortions occurring in the amebas (rounding up, pseudopods disappearing, and cellular organelles swelling) upon fixation. Achievement of normal ameboid shape in recent glycerination work (15) led us to attempt other electron microscope fixation techniques, resulting in a surprising preservation of A. proteus with a unique orientation of thick and thin filaments in the ectoplasmic region.     

Phylogenetic analyses of the rbcL sequences from haptophytes and heterokont algae suggest their chloroplasts are unrelated

Using the large subunit of RuBisCo (rbcL) sequences from cyanobacteria, proteobacteria, and diverse groups of algae and green plants, we evaluated the plastid relationship between haptophytes and heterokont algae. The rbcL sequences were determined from three taxa of heterokont algae (Bumilleriopsis filiformis, Pelagomonas calceolata, and Pseudopedinella elastica) and added to 25 published sequences to obtain a data set comprising 1,434 unambiguously aligned sites (approximately 98% of the total rbcL gene). Higher levels of mutational saturation in third codon positions were observed by plotting the pairwise substitutions with and without corrections for multiple substitutions at the same site for first and second codon positions only and for third positions only. In accordance with this finding phylogeny reconstructions were completed by omitting third codon positions, thus using 956 bp in weighted-parsimony and maximum-likelihood analyses. The midpoint-rooted phylogenies showed two major clusters, one containing cyanobacteria, glaucocystophytes, a phototrophic euglenoid, chlorophytes, and embryophytes (the green lineage), the other containing proteobacteria, haptophytes, red algae, a cryptophyte, and heterokont algae (the non-green lineage). In the nongreen lineage, the haptophytes formed a sister group to the clade containing heterokont algae, red algae, and the cryptophyte Guillardia theta. This branching pattern was well supported in terms of bootstrap values in weighted- parsimony and maximum-likelihood analyses (100% and 92%, respectively). However, the phylogenetic relationship among red algae, heterokonts, and a cryptophyte taxon was not especially well resolved. A four- cluster analysis was performed to further explore the statistical significance of the relationship between proteobacteria, red algae (including and excluding Guillardia theta), haptophytes, and heterokont algae. This test strongly favored the hypothesis that the heterokonts and red algae are more closely related to each other than either is to proteobacteria or haptophytes. Hence, this molecular study based on a plastid-encoded gene provides additional evidence for a distant relationship between haptophytes and the heterokont algae. It suggests an evolutionary scenario in which the ancestor of the haptophyte lineage engulfed a phototrophic eukaryote and, more recently, the heterokont lineage became phototrophic by engulfing a red alga.      

Variation in the harvest index of tropical maize: evaluation of recent evidence from Mexico and Malawi

In temperate zones, the potential grain yield of wheat has increased during the twentieth century owing to progressive increases in the harvest index of new varieties, which are principally associated with reduction in plant stature. Crop biomass has not increased substantially. In contrast, the potential grain yield of maize in the USA has increased owing to progressive increases in biomass, principally associated with selection for grain yield at higher population density. Harvest index was already around 0.5 for recommended varieties in 1930, and has not increased significantly since. However, for both crops, the harvest index of a given variety has proved to be a highly‐heritable character, except under severe stress. Less is known about the physiology of tropical maize. This paper reviews evidence from Mexico and Malawi that tropical maize can respond to selection for reduced stature following the same pattern as temperate wheat, but, under other circumstances, the magnitude of harvest index is not highly heritable, varying inconsistently with season, management and environment. It is proposed that these differences arise out of the unique vulnerability of the grain‐setting process around flowering. The plasticity of harvest index under long, favourable conditions, however, remains to be explained, although it is probably also related to the events around grain setting. Nevertheless, to the subsistence farmer, higher harvest index may not be a high priority in crop improvement, because of the need for large quantities of high‐quality stover.     

Morphological Constraints of Shoot Demography of a Clonal Plant: Extra- and Intravaginal Tillers of Festuca rubra

Abstract Festuca rubra forms tillers in two different ways: extravaginally and intravaginally. Demography of these two tiller types was observed in seventeen selected tussocks of Festuca rubra s.s. over four growing seasons. Extravaginal tillers were bigger at birth and on the average produced twice as many daughter tillers per tiller. In general, the natality and mortality of extravaginal tillers were less regular than that of intravaginal tillers. Overall tillering rate per tiller was correlated with the density of the surrounding vegetation; mortality, natality and tiller life span were not. High density of the surrounding vegetation did not result in increased formation of extravaginal tillers. The proportion of the extravaginal tillers was not correlated with the density of the F. rubra tussocks. There is no evidence for foraging by extravaginal tillers, but they do act as founders of small clusters of tillers.     

A molecular dynamics study of the effect of glycosidic linkage type in the hemicellulose backbone on the molecular chain flexibility

The macromolecular conformation of the constituent polysaccharides in lignocellulosic biomass influences their supramolecular interactions, and therefore their function in plants and their performance in technical products. The flexibility of glycosidic linkages from the backbone of hemicelluloses was studied by evaluating the conformational freedom of the φ and ψ dihedral angles using molecular dynamic simulations, additionally selected molecules were correlated with experimental data by nuclear magnetic resonance spectroscopy. Three types of β‐(1→4) glycosidic linkages involving the monosaccharides (Glcp, Xylp and Manp) present in the backbone of hemicelluloses were defined. Different di‐ and tetrasaccharides with combinations of such sugar monomers from hemicelluloses were simulated, and free energy maps of the φ – ψ space and hydrogen‐bonding patterns were obtained. The glycosidic linkage between Glc‐Glc or Glc‐Man (C‐type) was the stiffest with mainly one probable conformation; the linkage from Man‐Man or Man‐Glc (M‐type) was similar but with an increased probability for an alternative conformation making it more flexible, and the linkage between two Xyl‐units (X‐type) was the most flexible with two almost equally populated conformations. Glycosidic linkages of the same type showed essentially the same conformational space in both disaccharides and in the central region of tetrasaccharides. Different probabilities of glycosidic linkage conformations in the backbone of hemicelluloses can be directly estimated from the free energy maps, which to a large degree affect the overall macromolecular conformations of these polymers. The information gained contributes to an increased understanding of the function of hemicelluloses both in the cell wall and in technical products.     

Distribution and conservation of mobile elements in the genus Drosophila

Essentially nothing is known of the origin, mode of transmission, and evolution of mobile elements within the genus Drosophila. To better understand the evolutionary history of these mobile elements, we examined the distribution and conservation of homologues to the P, I, gypsy, copia, and F elements in 34 Drosophila species from three subgenera. Probes specific for each element were prepared from D. melanogaster and hybridized to genomic DNA. Filters were washed under conditions of increasing stringency to estimate the similarity between D. melanogaster sequences and their homologues in other species. The I element homologues show the most limited distribution of all elements tested, being restricted to the melanogaster species group. The P elements are found in many members of the subgenus Sophophora but, with the notable exception of D. nasuta, are not found in the other two subgenera. Copia-, gypsy-, and F-element homologues are widespread in the genus, but their similarity to the D. melanogaster probe differs markedly between species. The distribution of copia and P elements and the conservation of the gypsy and P elements is inconsistent with a model that postulates a single ancient origin for each type of element followed by mating-dependent transmission. The data can be explained by horizontal transmission of mobile elements between reproductively isolated species.      

A New Entodiniomorphid Ciliate,Troglocorys cava n. g., n. sp., from the Wild Eastern Chimpanzee (Pan troglodytes schweinfurthii) from Uganda

ABSTRACT. Troglocorys cava n. g., n. sp. is described from the feces of wild eastern chimpanzee, Pan troglodytes schweinfurthii, in Uganda. This new species has a spherical body with a frontal lobe, a long vestibulum, a cytoproct located at the posterior dorsal side of the body, an ovoid macronucleus, a contractile vacuole near the cytoproct, and a large concavity on the left surface of the body. Buccal ciliature is non‐retractable and consists of three ciliary zones: an adoral zone surrounding the vestibular opening, a dorso‐adoral zone extending transversely at the basis of the frontal lobe, and a vestibular zone longitudinally extending in a gently spiral curve to line the surface of the vestibulum. Two non‐retractable somatic ciliary zones comprise arches over the body surface: a short dorsal ciliary arch extending transversely at the basis of the frontal lobe and a wide C‐shaped left ciliary arch in the left concavity. Because of the presence of three ciliary zones in the non‐retractable buccal ciliature, the present genus might be a member of the family Blepharocorythidae, but the large left concavity and the C‐shaped left ciliary arch are unique, such structures have never been described from other blepharocorythids.     

CysK2 from Mycobacterium tuberculosis Is an O-Phospho-l-Serine-Dependent S-Sulfocysteine Synthase

Mycobacterium tuberculosis is dependent on cysteine biosynthesis, and reduced sulfur compounds such as mycothiol synthesized from cysteine serve in first-line defense mechanisms against oxidative stress imposed by macrophages. Two biosynthetic routes to l-cysteine, each with its own specific cysteine synthase (CysK1 and CysM), have been described in M. tuberculosis, but the function of a third putative sulfhydrylase in this pathogen, CysK2, has remained elusive. We present biochemical and biophysical evidence that CysK2 is an S-sulfocysteine synthase, utilizing O-phosphoserine (OPS) and thiosulfate as substrates. The enzyme uses a mechanism via a central aminoacrylate intermediate that is similar to that of other members of this pyridoxal phosphate-dependent enzyme family. The apparent second-order rate of the first half-reaction with OPS was determined as k_max/K_s = (3.97 × 10³) ± 619 M⁻¹ s⁻¹, which compares well to the OPS-specific mycobacterial cysteine synthase CysM with a k_max/K_s of (1.34 × 10³) ± 48.2. Notably, CysK2 does not utilize thiocarboxylated CysO as a sulfur donor but accepts thiosulfate and sulfide as donor substrates. The specificity constant k_cat/K_m for thiosulfate is 40-fold higher than for sulfide, suggesting an annotation as S-sulfocysteine synthase. Mycobacterial CysK2 thus provides a third metabolic route to cysteine, either directly using sulfide as donor or indirectly via S-sulfocysteine. Hypothetically, S-sulfocysteine could also act as a signaling molecule triggering additional responses in redox defense in the pathogen upon exposure to reactive oxygen species during dormancy.     

A survey of chlortetracycline concentration in feed and its residue in chicken egg in commercial layer farms

The worldwide increase in the use of antibiotics as an integral part of poultry and livestock production industry has recently received increasing attention as a contributory factor in the international emergence of antibiotic-resistant bacteria in human beings. To gauge the presence of the aforementioned scenario in the Indian context, a preliminary survey was conducted to assess the use of chlortetracycline (CTC) in 12 commercial layer farms and to quantify and confirm its residue in the egg. Samples of feed and eggs were collected at day 0 (prior to CTC addition), 3rd, 5th and 7th day during treatment and on the 9th and 14th day (2nd and 7th day after withdrawal of CTC) from each of the 12 commercial poultry farms studied. Concentration of CTC in feed was significantly (P<0.01) high on the 3rd, 5th and 7th day. On the 9th day and 14th day CTC concentration in feed was significantly (P<0.01) lower compared to the earlier 3 days studied. A highly significant difference (P<0.01) of the antibiotic residue in egg was observed in all the 5 days with high residual levels of CTC in egg. CTC in feed and its residue in egg were detected even on the 9th and 14th day respectively.