Trophic structure of a coastal fish community determined with diet and stable isotope analyses

A combination of dietary guild analysis and nitrogen (δ¹⁵N) and carbon (δ¹³C) stable‐isotope analysis was used to assess the trophic structure of the fish community in Rhode Island and Block Island Sounds, an area off southern New England identified for offshore wind energy development. In the autumn of 2009, 2010 and 2011, stomach and tissue samples were taken from 20 fish and invertebrate species for analysis of diet composition and δ¹⁵N and δ¹³C signatures. The food chain in Rhode Island and Block Island Sounds comprises approximately four trophic levels within which the fish community is divided into distinct dietary guilds, including planktivores, benthivores, crustacivores and piscivores. Within these guilds, inter‐species isotopic and dietary overlap is high, suggesting that resource partitioning or competitive interactions play a major role in structuring the fish community. Carbon isotopes indicate that most fishes are supported by pelagic phytoplankton, although there is evidence that benthic production also plays a role, particularly for obligate benthivores such as skates Leucoraja spp. This type of analysis is useful for developing an ecosystem‐based approach to management, as it identifies species that act as direct links to basal resources as well as species groups that share trophic roles.     

Characterization and structure of genes for proteases A and B from Streptomyces griseus.

Protease A and protease B are extracellular proteins which are secreted by Streptomyces griseus. The genes encoding protease A (sprA) and protease B (sprB) were isolated from an S. griseus genomic library by using a synthetic oligonucleotide probe. Fragments containing sprA and sprB were characterized by hybridization and demonstration of proteolytic activity in Streptomyces lividans. Each DNA sequence contains a large open reading frame with the coding region of the mature protease situated at its carboxy terminus. The amino terminus of each reading frame appears to encode a 38-amino-acid signal peptide followed by a 76- or 78-amino-acid polypeptide, a propeptide, which is joined to the mature protease. Strong homology between the coding regions of the protease genes suggests that sprA and sprB originated by gene duplication.     

In vivo and in vitro expression of an interleukin 2 receptor by murine B and T lymphocytes

Interleukin 2 (IL 2), which is well established to be a T cell growth factor, has more recently been shown to stimulate B lymphocyte growth and differentiation in vitro. Responsiveness of B and T cells to IL 2 has been associated with expression of a cell membrane IL 2 receptor (IL 2R). To investigate the role of IL 2 in B cell growth and differentiation in vivo, a system was used in which the injection of mice with a goat antibody to mouse IgD (GaM delta) induces polyclonal T-independent B cell proliferation first, and later induces polyclonal T-dependent B cell proliferation and IgG secretion. IL 2R expression by splenic B and T lymphocytes from GaM delta injected mice was studied by a dual label immunofluorescence technique. Although GaM delta was found to be a strong inducer of B cell IL 2R expression in vitro, even in serum-free medium, and stimulated up to 50% of splenic T cells to express considerable quantities of IL 2R in vivo, it failed to induce more than minimal B cell IL 2R expression in vivo. Concanavalin A and bacterial lipid A also induced B cells to express IL 2R to a much greater extent in vitro than in vivo. Although these agents and GaM delta acted synergistically to stimulate B cell IL 2R expression both in vitro and in vivo, a single agent induced B cell IL 2R expression to a considerably greater extent in vitro than did all three agents acting together in vivo. In vitro GaM delta-induced B cell IL 2R expression was not suppressed by inclusion of IL 2 in the culture medium but was suppressed by the presence of 10% normal mouse serum or plasma. These observations suggest that polyclonal T-dependent B cell proliferation and antibody secretion may not require an interaction between B cells and IL 2; the in vivo environment may downregulate IL 2R expression by B cells: and in vivo B cell IL 2R expression and consequently, induction of B cell responsiveness to IL 2, may require stimuli beyond those sufficient to induce B cell IL 2R expression and IL 2 responsiveness in vitro.     

Proliferation of T lymphocytes in response to interleukin 2 varies with their state of activation

The interleukin 2 (IL 2) receptor on T lymphocytes can be upregulated by a variety of stimuli including antigen, lectin, and IL 2 itself. In this report, the direct binding of radiolabeled IL 2 and a quantitative bioassay of T cell responsiveness to IL 2 were used to determine the biological significance of upregulation of the murine IL 2 receptor. Antigen and lectin, and to a lesser extent IL 2, were found to cause an increase in the expression of the high affinity form of the IL 2 receptor on both a T cell clone and concanavalin A-induced T cell blasts. A 2-day stimulation with antigen resulted in an increase in the sensitivity of the T cell clone to IL 2, whereas activation with IL 2 caused a decrease in the sensitivity of these cells to subsequent stimulation with IL 2. Comparison of the direct binding and the functional data revealed that IL 2-preactivated T cells required a greater number of occupied high affinity IL 2 receptors to achieve a given fractional response than did unactivated T cells. These observations suggest that the sensitivity with which a T cell responds to IL 2 is not determined solely by the number of high affinity IL 2 receptors it bears.     

Aminoacylation of tRNA and Protein Turnover in Nitrateand Sulphate-Deficient Spirodela polyrhiza

Cultures of Spirodela polyrhiza were maintained in completeHoagland's medium at 25°C in continuous light. Nitrate-and sulphate-deficient plants were cultured in media containing1/20 Hoagland's nitrate and 1/200 Hoagland's sulphate respectively.After 10 days of growth the plants were examined for total aminoacyltRNA levels. Turnover of leucyl-tRNA and rates of protein synthesiswere assessed by pulse feeding [³H]leucine. Control and nutrient-deficientplants had similar levels of tRNA-associated amino acids. Howeverthe amounts of tRNA, expressed on a fresh weight basis, weresignificantly lower in nitrate- and sulphate-deficient plants.Although the specific radioactivities of leucyltRNA were highestin deficient cultures the rate of turnover of this pool wasless than non-deficient control or nitrate- and sulphate-supplementedplants. Calculation of the average rate constants for proteinsynthesis and degradation showed that nitrate deficiency, althoughnot affecting rates of synthesis, supported rates of proteindegradation that were higher than control cultures. ¹ Present address: The Biological Laboratories, Harvard University,16 Divinity Avenue, Cambridge, Massachusetts 02138, U.S.A. (Received March 7, 1983; Accepted August 16, 1983)     

Alloreactive T cells from individual soft agar colonies specific for guinea pig Ia antigens. II. Cellular and molecular requirements for optimal proliferative responses

We have investigated the cellular and molecular requirement for optimal proliferative responses of several alloreactive T cell lines that were derived from individual soft agar colonies and were specific for guinea pig Ia antigens. Optimal proliferation of several colonies was observed in cultures containing purified allogeneic macrophages and growth factor(s) present in supernatant fluids of Con A-activated T cells (Con A-S). Significant proliferative responses of these alloreactive T cell colonies were also routinely detected in cultures only supplemented with unfractionated irradiated allogeneic peritoneal exudate cell (PEC). The T cell component of the stimulator cell population was crucial for these responses by producing necessary growth factor(s) endogenously in the culture. Thus, 2 signals, allogeneic Ia antigens and growth factor(s), were required for optimal proliferative responses of these alloreactive T cell colonies. Furthermore, macrophage-associated Ia antigen was more efficient than B cell-associated Ia for these responses. The requirement for allogeneic Ia antigen was not absolute, since the colonies could easily be expanded when the cultures were supplemented with irradiated syngeneic PEC and the T cell mitogens, Con A or PHA. The effect of the mitogen was mediated via the T cells in the irradiated PEC, since removal of the T cells from these PEC markedly reduced the responses. Thus, it is likely that a nonspecific signal(s) presumably from T cells can promote proliferation of alloreactive T cell colonies in the absence of allogeneic Ia antigen. These results suggest 2 mechanisms of activation of these alloreactive T cells.     

Symptomatology and Histopathology of Soybean Roots Infected by Pratylenchus scribneri and P. alleni

Size of lesions caused by Pratylenchus scribneri on roots of ''Clark 63'' soybean was correlated with nematode colony size within roots. A single nematode was capable of causing a detectable lesion. When a root became highly necrotic and shrunken, few nematodes but numerous eggs remained in the tissue. In histological sections made 5, 11, 18, and 45 d after planting, P. scribneri was located entirely within the cortex and generally was oriented longitudinally to the vascular cylinder, either outstretched in the same plane or coiled through several cells. Nematodes moved intracellularly, causing extensive rupturing of cell walls, retraction and disappearance of cytoplasm, and thickening of cell walls and necrosis of cells around feeding sites. Depth of penetration within the cortex and necrosis of cells increased with time after infection, eventually resulting in formation of cavities in the cortex and occasional secondary injury to the endodermis. Stele tissue was unaffected by feeding, and damage to the epidermis was limited to nematode entry points. Orientation of P. alleni and histopathology of its infection at 45 days were identical to those of P. scribneri, except that there was no injury to the endodermis.     

Races of the Barley Root-Knot Nematode,Meloidogyne naasi. II. Developmental Rates

The developmental rates of the five newly designated races of Meloidogyne naasi were compared on barley, oat and sorghum. Races 1, 2, 3 and 4 developed and reproduced on both barley and oat but not on sorghum. Race 5 developed and reproduced readily on sorghum but poorly on oat. A more rapid rate of development of Race 5 on both barley and sorghum than that of other races on barley demonstrated that Race 5 has a shorter life cycle than do Races 1-4.