Mycobacterial cell wall: Structure and role in natural resistance to antibiotics

Abstract Mycobacteria show a high degree of intrinsic resistance to most antibiotics and chemotherapeutic agents. The low permeability of the mycobacterial cell wall, with its unusual structure, is now known to be a major factor in this resistance. Thus hydrophilic agents cross the cell wall slowly because the myobacterial porin is inefficient in allowing the permeation of solutes and exists in low concentration. Lipophilic agents are presumably slowed down by the lipid bilayer which is of unusually low fluidity and abnormal thickness. Nevertheless, the cell wall barrier alone cannot produce significant levels of drug resistance, which requires synergistic contribution from a second factor, such as the enzymatic inactivation of drugs.     

Global mangrove root production,its controls and roles in the blue carbon budget of mangroves

Mangroves are among the most carbon-dense ecosystems worldwide. Most of the carbon in mangroves is found belowground, and root production might be an important control of carbon accumulation, but has been rarely quantified and understood at the global scale. Here, we determined the global mangrove root production rate and its controls using a systematic review and a recently formalised, spatially explicit mangrove typology framework based on geomorphological settings. We found that global mangrove root production averaged ~770 ± 202 g of dry biomass m⁻² year⁻¹ globally, which is much higher than previously reported and close to the root production of the most productive tropical forests. Geomorphological settings exerted marked control over root production together with air temperature and precipitation (r² ≈ 30%, p < .001). Our review shows that individual global changes (e.g. warming, eutrophication, drought) have antagonist effects on root production, but they have rarely been studied in combination. Based on this newly established root production rate, root-derived carbon might account for most of the total carbon buried in mangroves, and 19 Tg C lost in mangroves each year (e.g. as CO₂). Inclusion of root production measurements in understudied geomorphological settings (i.e. deltas), regions (Indonesia, South America and Africa) and soil depth (>40 cm), as well as the creation of a mangrove root trait database will push forward our understanding of the global mangrove carbon cycle for now and the future. Overall, this review presents a comprehensive analysis of root production in mangroves, and highlights the central role of root production in the global mangrove carbon budget.     

Family and Community in Ireland.

Family and Community in Ireland. Conrad M. Arensberg and Solon T. Kimball. Third edition, with. new introduction by Anne Byrne, Ricca Edmondson, and Tony Varley. Ennis, Ireland: Clasp Press, 2001. 417 pp.     

Imprecise exposure assessment and the sample size requirements of case-control studies of residential magnetic field exposure and cancer in adults

A computer program simulating case-control studies is described. It is used to estimate the minimum sample size required and to assess how this is affected by imprecise exposure assessment. In particular, the consequences of neglecting measurements of nonresidential exposure in case-control studies of residentially exposed adults are investigated. According to this model, while the consequent loss of power is not as large as was predicted by algebraic methods, it would be unwise to neglect it when planning a study. © 1995 Wiley-Liss, Inc.     

Cell lineage patterns and homeotic gene activity during Antirrhinum flower development

Background: Homeotic genes controlling the identity of flower organs have been characterized in several plant species. To determine whether cells expressing these genes are specified to follow particular developmental fates, we have studied the pattern of cell lineages in developing flowers of Antirrhinum. Each flower has four whorls of organs, and progenitor cells of these can be marked at particular stages of development using a temperature-sensitive transposon. This allows the cell lineages in the flower to be followed, as well as giving information about rates of cell division.Results We show here that, prior to the emergence of organ primordia, cells in the floral meristem have not been allocated organ identities. After this time, lineage restrictions arise between whorls, correlating with the onset of expression of genes that control organ identity. A further lineage restriction appears slightly later on, between the dorsal and ventral surfaces of the petal. Our results further suggest that the rates of cell division fluctuate during key stages of meristem development, perhaps as a consequence of meristem-identity gene expression.Conclusion The patterns of lineage restriction and organ-identity gene expression in early floral meristems are consistent with some cells being allocated specific identities at about this stage of development. Plant cells cannot move relative to each other, so lineage restrictions in plants may reflect particular orientations and/or rates of growth at boundary regions.     

Initial evaluation of the non-sulfhydryl-containing converting enzyme inhibitor MK-521 in hypertensive humans

MK-521 is a new orally active, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor. Single doses of 2.5, 5.0, 10.0, and 20.0 mg were administered to nine hypertensive patients alternating with placebo. All doses of MK-521 caused profound suppression of ACE activity for more than 24 h and decreased standing diastolic blood pressure for more than 12 h without changes in pulse rate. Although there was no further reduction in blood pressure with doses above 5.0 mg, the duration of action was prolonged for more than 24 h with the higher doses. Serum MK-521 concentrations increased with dosage, and ACE was inhibited maximally at concentrations above 10 ng/ml. In this initial study, MK-521 was well tolerated and proved to be a potent and long-acting antihypertensive agent.