Mannose-6-Phosphate Reductase,a Key Enzyme in Photoassimilate Partitioning,Is Abundant and Located in the Cytosol of Photosynthetically Active Cells of Celery (Apium graveolens L.) Source Leaves

Mannitol, a major photosynthetic product and transport carbohydrate in many plants, accounts for approximately 50% of the carbon fixed by celery (Apium graveolens L.) leaves. Previous subfractionation studies of celery leaves indicated that the enzymes for mannitol synthesis were located in the cytosol, but these data are inconsistent with that published for the sites of sugar alcohol synthesis in other families and taxa, including apple (Malus) and a brown alga (Fucus). Using antibodies to a key synthetic enzyme, NADPH-dependent mannose-6-phosphate reductase (M6PR), and immunocytochemical techniques, we have resolved both the inter-cellular and intracellular sites of mannitol synthesis. In leaves, M6PR was found only in cells containing ribulose-1,5-bisphosphate carboxylase/oxygenase. M6PR was almost exclusively cytosolic in these cells, with the nucleus being the only organelle to show labeling. The key step in transport carbohydrate biosynthesis that is catalyzed by M6PR displays no apparent preferential association with vascular tissues or with the bundle sheath. These results show that M6PR and, thus, mannitol synthesis are closely associated with the distribution of photosynthetic carbon metabolism in celery leaves. The principal role of M6PR is, therefore, in the assimilation of carbon being exported from the chloroplast, and it seems unlikely that this enzyme plays even an indirect role in phloem loading of mannitol.     

Investigation into the hypogonadism of the obese mouse (genotype ob/ob)

Features of the reproductive axis in the genetically hypogonadal, obese mouse (genotype, ob/ob) were examined at 5-8 months of age and compared with those of wild-type litter mates. Hypothalamic concentrations of dopamine and 5-hydroxytryptamine were normal. Those of 5-hydroxyindoleacetic acid, noradrenaline and LH-RH were raised. LH-RH was biologically active. Pituitary concentration of LH was normal, but that of FSH was raised. Serum concentrations of LH and FSH, compared with those of wild-type animals, were normal and low, respectively. Gonad and accessory sex organs weights were reduced. These findings suggest that the release of FSH but not LH is defective in the ob/ob mouse. Preliminary in-vitro experiments indicated that the pituitary gland responded normally or even supernormally towards LH-RH in its release of LH. The defect in the reproductive axis of the obese mouse may be due to inadequate release of LH-RH although an insensitivity of the pituitary gland towards LH-RH in its release of FSH cannot be excluded.     

Salmonella in wildlife from Trinidad and Grenada, W.I.

Forty-four of 219 animals from Trinidad and Grenada, W.I., yielded 20 serotypes of Salmonella, 16 of which are known to have been associated with human infection in the United States in recent years. Toads (Bufo marinus) provided the greatest number of isolates. Other carriers were mammals, vultures, lizards, a tree-frog and a cave cockroach.     

Structure-based library design and the discovery of a potent and selective mast cell β-tryptase inhibitor as an oral therapeutic agent

A solid phase combinatorial library was designed based on X-ray structures and in-silico models to explore an inducible S4+ pocket, which is formed by a simple side-chain rotation of Tyr95. This inducible S4+ pocket is unique to β-tryptase and does not exist for other trypsin-like serine proteases of interest. Therefore, inhibitors utilizing this pocket have inherent advantages for being selective against other proteases in the same family. A member of this library was found to be a potent and selective β-tryptase inhibitor with a suitable pharmacokinetic profile for further clinical evaluation.     

Stochastic models for phylogenetic trees on higher-order taxa

Simple stochastic models for phylogenetic trees on species have been well studied. But much paleontology data concerns time series or trees on higher-order taxa, and any broad picture of relationships between extant groups requires use of higher-order taxa. A coherent model for trees on (say) genera should involve both a species-level model and a model for the classification scheme by which species are assigned to genera. We present a general framework for such models, and describe three alternate classification schemes. Combining with the species-level model of Aldous and Popovic (Adv Appl Probab 37:1094–1115, 2005), one gets models for higher-order trees, and we initiate analytic study of such models. In particular we derive formulas for the lifetime of genera, for the distribution of number of species per genus, and for the offspring structure of the tree on genera. David Aldous’s research was supported by NSF Grant DMS-0704159.     

Impact of soil warming and shading on colonization and community structure of arbuscular mycorrhizal fungi in roots of a native grassland community

Arbuscular mycorrhizal (AM) fungi have a major influence on the structure, responses and below‐ground C allocation of plant communities. Our lack of understanding of the response of AM fungi to factors such as light and temperature is an obstacle to accurate prediction of the impact of global climate change on ecosystem functioning. In order to investigate this response, we divided a grassland site into 24 plots, each either unshaded or partly shaded with soil either unheated or heated by 3°C at 2 cm depth. In both short‐term studies in spring and autumn, and in a 1‐year‐long study, we measured root length colonization (L_RC) by AM and non‐AM fungi. For selected root samples, DNA sequences were amplified by PCR with fungal‐specific primers for part of the small sub‐unit (SSU) rRNA gene. In spring, the total L_RC increased over 6 weeks from 12% to 25%. Shading significantly reduced AM but increased non‐AM fungal colonization, while soil warming had no effect. In the year‐long study, colonization by AM fungi peaked in summer, whereas non‐AM colonization peaked in autumn, when there was an additive effect of shading and soil warming that reduced AM but increased non‐AM fungi. Stepwise regression revealed that light received within the 7 days prior to sampling was the most significant factor in determining AM L_RC and that mean temperature was the most important influence on non‐AM L_RC. Loglinear analysis confirmed that there were no seasonal or treatment effects on the host plant community. Ten AM fungal sequence types were identified that clustered into two families of the Glomales, Glomaceae and Gigasporaceae. Three other sequence types were of non‐AM fungi, all Ascomycotina. AM sequence types showed seasonal variation and shading impacts: loglinear regression analysis revealed changes in the AM fungal community with time, and a reduction of one Glomus sp. under shade, which corresponded to a decrease in the abundance of Trifolium repens. We suggest that further research investigating any impacts of climate change on ecosystem functioning must not only incorporate their natural AM fungal communities but should also focus on niche separation and community dynamics of AM fungi.