Sugars and plant innate immunity

Sugars are involved in many metabolic and signalling pathways in plants. Sugar signals may also contribute to immune responses against pathogens and probably function as priming molecules leading to pathogen-associated molecular patterns (PAMP)-triggered immunity and effector-triggered immunity in plants. These putative roles also depend greatly on coordinated relationships with hormones and the light status in an intricate network. Although evidence in favour of sugar-mediated plant immunity is accumulating, more in-depth fundamental research is required to unravel the sugar signalling pathways involved. This might pave the way for the use of biodegradable sugar-(like) compounds to counteract plant diseases as cheaper and safer alternatives for toxic agrochemicals.     

Sugars,cytolitols and seagrass phylogeny

Seagrasses of the Zannichelliaceae accumulate larger amounts and a greater range of cyclitols than do other seagrasses. Amphibolis, Cymodocea, Syringodium and Thalassodendron contained up to 10% dry weight of compounds identified as 1-chiro-inositol, muco-inositol and a methyl-O-muco-inositol, in addition to traces of myo-inositol. These compounds were not utilised as carbohydrate reserves and there is some evidence that they accumulated as by-products of an unusual glucose cyclisation mechanism. Sucrose can accumulate to more than 50% of dry weight in underground rhizomes and roots of these and other seagrasses and it was also the major initial product of photosynthesis in most seagrasses leaves.A distinct phylogenetic trend, based on their cyclitols, can be distinguished within the seagrass. This is discussed in terms of seagrass origins and biogeography.     

Sugars and desiccation tolerance in seeds

Soluble sugars have been shown to protect liposomes and lobster microsomes from desiccation damage, and a protective role has been proposed for them in several anhydrous systems. We have studied the relationship between soluble sugar content and the loss of desiccation tolerance in the axes of germinating soybean (Glycine max L. Merr. cv Williams), pea (Pisum sativum L. cv Alaska), and corn (Zea mays L. cv Merit) axes. The loss of desiccation tolerance during imbibition was monitored by following the ability of seeds to germinate after desiccation following various periods of preimbibition and by following the rates of electrolyte leakage from dried, then rehydrated axes. Finally, we analyzed the soluble sugar contents of the axes throughout the transition from desiccation tolerance to intolerance. These analyses show that sucrose and larger oligosaccharides were consistently present during the tolerant stage, and that desiccation tolerance disappeared as the oligosaccharides were lost. The results support the idea that sucrose may serve as the principal agent of desiccation tolerance in these seeds, with the larger oligosaccharides serving to keep the sucrose from crystallizing.     

Paradigms of plasmid organization

Plasmids are extrachromosomal elements built from a selection of generally quite well understood survival and propagation functions, including replication, partitioning, multimer resolution, post-segregational killing and conjugative transfer. Evolution has favoured clustering of these modules to form plasmid cores or backbones. Co-regulation of these core genes can also provide advantages that favour retention of the backbone organization. Tumour-inducing and symbiosis-determining plasmids appear to co-regulate replication and transfer in response to cell density, both being stimulated at high density. Broad-host-range plasmids of the IncP-1 group, on the other hand, have autogenous control circuits, which allow a burst of expression during establishment in a new host, but a minimum of expression during maintenance. The lessons that plasmids have for clustering and co-regulation may explain the logic and organization of many small bacterial genomes currently being investigated.     

Sugars, signalling, and plant development

Like all organisms, plants require energy for growth. They achieve this by absorbing light and fixing it into a usable, chemical form via photosynthesis. The resulting carbohydrate (sugar) energy is then utilized as substrates for growth, or stored as reserves. It is therefore not surprising that modulation of carbohydrate metabolism can have profound effects on plant growth, particularly cell division and expansion. However, recent studies on mutants such as stimpy or ramosa3 have also suggested that sugars can act as signalling molecules that control distinct aspects of plant development. This review will focus on these more specific roles of sugars in development, and will concentrate on two major areas: (i) cross-talk between sugar and hormonal signalling; and (ii) potential direct developmental effects of sugars. In the latter, developmental mutant phenotypes that are modulated by sugars as well as a putative role for trehalose-6-phosphate in inflorescence development are discussed. Because plant growth and development are plastic, and are greatly affected by environmental and nutritional conditions, the distinction between purely metabolic and specific developmental effects is somewhat blurred, but the focus will be on clear examples where sugar-related processes or molecules have been linked to known developmental mechanisms.     

Paradigms of expected failure

This study explores the outsourcing and offshoring of clinical trials and how they interconnect with the dynamics of drug development and regulation in the United States. I focus on the activities of United States-based contract research organizations, which make up a specialized global clinical trials industry focusing on the recruitment of human subjects and investigators. Tracking this industry’s activities in eastern Europe and Latin America, two clinical trial market ‘growth regions,’ I address the strategies of evidence-making that inform clinical trial offshoring. I also show how aspects of the clinical trial model—in which failures to predict safety outcomes or a paradigm of expected failure—are being exported along with the offshored trial. The clinical trials industry is a crucial, highly mobile, and profitable arm of the global pharmaceutical industry. Where state agencies furnish limited or no health care, drug developers claim that trial expansion and experiments have become social goods in themselves. But questions remain: How is drug value and research integrity maintained? And how do the results of clinical trials strengthen or undermine the delivery of affordable and effective interventions? As this essay shows, clinical trials are not only hypothesis-testing instruments; they are operative environments redistributing resources and occasioning tense medical and social fields. In highlighting the inefficiencies and uncertainties of global drug development, this study points to problems in the operational model of drug development and in systems of human protection. It also considers new forms of accountability at the nexus of private sector science and public health.     

Shifting Narratives and Mutable Meanings

In and Out of Africa . 1993. 59 minutes, color. A film by Ilisa Barbash and Lucien Taylor. For information contact University of California Extension Center for Media and Independent Learning, 2000 Center Street, Fourth Floor, Berkeley, CA 94704, 510–642–0460.     

Neotropical Frog Biogeography: Paradigms and Problems

SYNOPSIS. The distributions and relationships of exemplary speciesgroups of the Neotropical frog genera Cycloramphus and Leptodactylusare discussed in terms of current biogeographic models. Fromthis exercise, the following conclusions emerge: (1) frog biogeographyis and will remain primarily a correlative science; (2) bothmorphological and genetic data are required to choose amongalternate biogeographic models; (3) frog speciation events significantlypredate recent distributional events complicating the understandingof past and recent distributions; (4) both data and theory areinadequate to completely understand Neotropical frog biogeographyat present.