Growth and nodulation of tropical food legumes in dilute solution culture

Twenty-two tropical food legumes were grown in dilute nutrient solution with or without rhizobium inoculation and supplied with either low or adequate amounts of inorganic N. Growth of legumes supplied with adequate inorganic N was generally satisfactory. However, solution phosphorus (P) concentration (15μM) was excessive for black gram, while the initial solution manganese concentration (1.8μM) was excessive for green gram. Growth responses to inoculation with rhizobium at low inorganic N supply were obtained in only 9 of the 22 legumes studied, and shoot dry matter yields were ≤ 51% of those obtained with adequate N supply. Poor growth by inoculated plants with a low N supply was attributed to failure of the inoculated strain of Bradyrhizobium to infect roots (lima bean and Mexican yam bean), to low nodule numbers (green gram, black gram and navy bean), or to excessive uptake of P (black gram, adzuki bean, pigeonpea, winged bean and cowpea cv. Vita 4) and/or manganese (green gram and black gram). High solution temperatures may have limited N fixation by some of the legumes, particularly chickpea.     

Production of α-Amylase by the Ruminal Anaerobic Fungus Neocallimastix frontalis

α-Amylase production was examined in the ruminal anaerobic fungus Neocallimastix frontalis. The enzyme was released mainly into the culture fluid and had temperature and pH optima of 55°C and 5.5, respectively, and the apparent K_m for starch was 0.8 mg ml⁻¹. The products of α-amylase action were mainly maltotriose, maltotetraose, and longer-chain oligosaccharides. No activity of the enzyme was observed towards these compounds or pullulan, but activity on amylose was similar to starch. Evidence for the endo action of α-amylase was also obtained from experiments which showed that the reduction in iodine-staining capacity and release in reducing power by action on amylose was similar to that for commercial α-amylase. Activities of α-amylase up to 4.4 U ml⁻¹ (1 U represents 1 μmol of glucose equivalents released per min) were obtained for cultures grown on 2.5 mg of starch ml⁻¹ in shaken cultures. No growth occurred in unshaken cultures. With elevated concentrations of starch (>2.5 mg ml⁻¹), α-amylase production declined and glucose accumulated in the cultures. Addition of glucose to cultures grown on low levels of starch, in which little glucose accumulated, suppressed α-amylase production, and in bisubstrate growth studies, active production of the enzyme only occurred during growth on starch after glucose had been preferentially utilized. When cellulose, cellobiose, glucose, xylan, and xylose were tested as growth substrates for the production of α-amylase (initial concentration, 2.5 mg ml⁻¹), they were found to be less effective than starch, but maltose was almost as effective. The fungal α-amylase was found to be stable at 60°C in the presence of low concentrations of starch (≤5%), suggesting that it may be suitable for industrial application.     

Use of recombination techniques to examine the structure of the csg locus of Myxococcus xanthus

Summary The technique of chromosome walking was used to isolate approximately 60 kb of DNA from the region containing the complementation group uncoordinated of Drosophila melanogaster, located in that part of the X chromosome which spans the euchromatin-heterochromatin junction. The cloned DNA can be divided into two distinct regions. The first contains sequences that are low copy number or unique and are largely conserved between strains. The second region is characterized by units repeated in tandem arrays and is polymorphic within, and between, strains. Each repetitive unit is separated by a member of an abundant sequence family, part of which is homologous to the ribosomal type 1 insertion sequence of D. melanogaster. The molecular organization of the cloned DNA was compared with that of sequences isolated from regions of intercalary heterochromatin and also with genes which have been characterized from more conventional euchromatic regions.     

Approaches to assessing and managing cumulative ecosystem change,with the Bay of Quinte as a case study: an essay

Rising concern for the future of humans and the earth's ecosystems provides the backdrop for an essay on approaches to assessing and managing ecosystem health. A review and critique of two rival metaphors of human health, illness and wellness, provide the staring point for evaluation of parallel approaches to the assessment and management of ecosystems. The limitations of the metaphors are noted for humans and ecosystems. The impact assessment and ecosystem approach concepts of ecosystem assessment and management are contrasted. As a case history, the nature and pace of change in the Bay of Quinte ecosystem are reviewed, spanning from colonization by the Empire Loyalists at the end of the 18th century through the current development of a remedial action plan for the ecosystem. The review includes the long-term scientific study of the Bay's response to point-source phosphorus control (Project Quinte) and the recent efforts to develop and implement a coordinated clean-up program (Remedial Action Plan). From the lessons of the Quinte experience, a framework is derived, combining the illness and wellness approaches to health. The framework deals with five topics: uncertainty and the precautionary principle; an ecosystem health scale; indicators of ecosystem health; maximum allowable change; and, regulation and planning. Uncertainty should not be used to justify inaction. A precautionary principle assumes that impacts will occur and places the burden of proof on the proponents of ecosystem disturbance. An ecosystem health scale is defined using current, original, and potential conditions. Restoration to the original condition is unlikely but provides a justifiable direction for actions to establish sustainability. Indicators of ecosystem health with sustainable ranges are preferred over end-points and thresholds. The concept of maximum allowable change is promoted with a tentative suggestion that a fifty percent rule might be used. Finally, an argument for the combined use of regulation and planning. Regulatory approaches tend to perpetuate confrontation. Planning can be used to lengthen the time-horizon from quarterly reports to generations and identify self-regulating codes of behaviour. The framework is briefly discussed and placed in a broader context linking humans and ecosystem, illness and wellness.Based on the text of a talk presented at the Cumulative Impact Assessment Workshop held in Toronto, Ontario, December 1992, and sponsored by the North Central Division of the American Fisheries Society.     

Recombinant human tumor necrosis factor mediates regression of a murine sarcoma in vivo via Lyt-2+ cells

Summary The role of an immune response in recombinant-human-tumor-necrosis-factor(rHTNF)-mediated regression of a weakly immunogenic, MCA-106 sarcoma in vivo was examined. C57BL/6 mice bearing established 10-day s.c. tumor were treated with single i.v. doses (8 g) of rHTNF. rHTNF administration resulted in marked hemorrhagic necrosis and subsequent regression of tumor in treated mice. Mice cured of MCA-106 sarcoma by rHTNF specifically rejected a subsequent challenge (5×10⁵ cells) of the same tumor (P<0.01) but not of the antigenically distinct, syngeneic MCA-105 sarcoma. Tumor bearers were depleted in vivo of selective T-cell subsets by the systemic administration of specific monoclonal antibodies before rHTNF therapy. rHTNF-induced regression, but not hemorrhagic necrosis of the MCA-106 sarcoma was blocked in mice depleted of Lyt-2⁺ cells, but not of L3T4⁺ cells. The in vivo role of T-cell subsets in rHTNF-mediated tumor regression is discussed.Howard Hughes Medical Institute Research Scholar