InsP(3)-mediated calcium release induced by heterologous expression of total chicory Leaf RNA

A calcium dependent-chloride current (I(ni)) was recorded in Xenopus oocytes injected with total RNA from chicory leaf tissues, following depolarization from -35 to +60 mV. However, the signal transduction mechanism mediating I(ni) is unknown. The development of this current was mimicked by intracellular injection of the second messenger InsP(3) in control (non-injected) oocytes. Moreover, InsP(3) injection after I(ni) rundown did not reinitiate the current. The same phenomenon was observed following a second injection into control oocytes. Measurement of InsP(3) production in injected oocytes showed a net increase in the InsP(3) level on depolarization. Moreover, extracellular application of caffeine (5 mM) significantly reduced the number of oocytes displaying I(ni). Also, extracellular application of U-73122, a potent PLC inhibitor, clearly reduced the occurrence of I(ni). These data provide the first evidence that the calcium homeostasis mechanism induced by heterologous expression of total RNA from chicory leaves involves the InsP(3) signaling pathway.     

Role of temperature as a triggering signal for organogenesis or somatic embryogenesis in wounded leaves of chicory cultured in vitro

Static liquid half-strength Murashige and Skoog medium, containing10.1 mM KCI instead of KNO3, 1.7 mM glutamine, microelements,vitamins, 60 mM sucrose, 0.1 //M a-naphthaleneacetic acid and2.5//M 2-isopentenyladenine allows either somatic embryo-genesisor shoot organogenesis along the borders of leaf incisions ofa Cichorium hybrid [Cichorium intybus L. x Cichorium endiviaL.). These phenomena are temperature-dependent and the latterpromotes the development of callus and shoots at 20 °C and25 °C instead of direct somatic embryogenesis at 35 °C.At 30 °C all types of morphogenesis are observed. After5 d of culture, cells grown at each temperature exhibit enlargednuclei with prominent nucleoli, fragmented vacuoles and densecytoplasm. However, at 25 °C, callose is restricted to woundedcells whereas at 35 °C some nearby mesophyll cells showa more or less complete callose sheath. On the 7th day, proembryosat 35 °C show a superficial network which is absent at 25°C on shoot primordia which are covered with a smooth precociousproto-derm. Why do activated cells undergo segmentation andsomatic embryogenesis at 35 °C instead of ordinary mitosiswith callus and shoot formation at 20 °C and 25 °C? Key words: Cichorium, morphogenesis, somatic embryos, tpmnpratnrp     

A four-proton-families model for pH-dependent enzyme activation: application to intestinal brush border sucrase.

Current concepts of pH-dependent enzyme function are expanded to consider enzymes with up to four key proton families. In an earlier paper the authors extended classical theory to explain the existence, in the acid ionization reaction, of two functionally distinct, V and K, proton families, exemplified by the 1988 sucrase three-proton-families model of Vasseur et al. They now propose that enzymes having two distinguishable proton families at each side of the pH-activity curves exist in nature although there is no previously published evidence of their existence. The resulting, more general, four-proton-families model is treated as a useful framework from which submodels can be derived by simplification, the simplest being the 1911 linear model of Michaelis and Davidsohn, which took into account two proton families out of the theoretical maximum of four proposed here. It is shown that whether a three-proton-families or a four-proton-families model can explain sucrase better is not merely a question of theory but also involves the practical question of having enough data, at each side of the pH spectrum, to permit making an unequivocal choice between the two alternatives. The paper concludes with a discussion of substrate-induced pK shifts according to both models.     

Polarity of annealing and structural analysis of the RNase H resistant alpha-5'-d[TACACA].beta-5'-r[AUGUGU] hybrid determined by high-field 1H, 13C, and 31P NMR analysis.

The novel hybrid duplex alpha-5'-d[TACACA]-3'.beta-5'-r[AUGUGU]-3' was analyzed extensively by 1D and 2D NMR methods. Two forms of the duplex exist in about an 80:20 ratio. Analysis of the exchangeable imino protons of the major component revealed that three AU and one AT base pair are present in addition to two GC base pairs, confirming that the duplex anneals in parallel orientation. The presence of the AT base pair, which can only be accounted for by a parallel duplex, was confirmed by a selective INEPT experiment, which correlated the thymidine imino proton to its C5 carbon. The lesser antiparallel form could be detected by exchangeable and nonexchangeable proton resonances in both strands. An exchange peak was observed in the NOESY spectrum for the thymidine methyl group resonance in both the predominant and lesser conformations, indicating the lifetime of the individual structures was on the millisecond time scale. The nonexchangeable protons of the predominant duplex were assigned by standard methods. The sugar pucker of the ribonucleosides was determined to be of the "S" type by a pseudorotation analysis according to Altona, with the J-couplings measured from the multiplet components of the phase-sensitive COSY experiment. The NOE pattern observed for the alpha-deoxynucleosides also suggested an S-type sugar pucker. The adoption of an S-type sugar pucker for both strands indicates that, in contrast to RNA.DNA duplexes formed exclusively from beta-nucleotides, the alpha-DNA.beta-RNA duplex may form a B-type helix. The 31P resonances of the alpha and beta strands have very different chemical shifts in the hybrid duplex and the difference persists above the helix melting temperature, indicating an intrinsic difference in 31P chemical shift for nucleotides differing only in the configuration about the glycosidic bond.     

A mechanistic approach for modeling temperature-dependent consumer-resource dynamics

Paramount to our ability to manage and protect biological communities from impending changes in the environment is an understanding of how communities will respond. General mathematical models of community dynamics are often too simplistic to accurately describe this response, partly to retain mathematical tractability and partly for the lack of biologically pleasing functions representing the model/environment interface. We address these problems of tractability and plausibility in community/environment models by incorporating the Boltzmann factor (temperature dependence) in a bioenergetic consumer-resource framework. Our analysis leads to three predictions for the response of consumer-resource systems to increasing mean temperature (warming). First, mathematical extinctions do not occur with warming; however, stable systems may transition into an unstable (cycling) state. Second, there is a decrease in the biomass density of resources with warming. The biomass density of consumers may increase or decrease depending on their proximity to the feasibility (extinction) boundary. Third, consumer biomass density is more sensitive to warming than resource biomass density (with some exceptions). These predictions are in line with many current observations and experiments. The model presented and analyzed here provides an advancement in the testing framework for global change scenarios and hypotheses of latitudinal and elevational species distributions.     

Practical importance for conservation of insect diversity in China

Insects are one of the most important groups in the natural world. They affect the life and welfare of humans in many different ways. While some insects are referred to as pests, others are beneficial to humans. For example, they may serve a function as pollinators of many cultivated plants, as natural enemies of harmful species, or as producers of valuable materials such as honey and silk. Several insect species, however, are not currently known as being harmful or beneficial. Nevertheless they are extremely important as essential components of both natural and modified ecosystems. In China, only 1% of insect species described are major pests. The majority of insects are either neutral or beneficial to humans. China, with its vast territory, diverse climate and ecosystems, is amongst the richest countries in insect diversity. However, as a result of the economic and population growth and development, Chinas insect diversity is now faced with habitat degradation, species extinction, and a decline in the natural enemies of harmful pests. These problems are due to the expansion of agriculture, urbanization, industrialization, pollution, mining, tourism, introduced species, hunting, and the illegal trade in endangered species. In order to exploit the beneficial components of insects as biological resources and to effectively control their harmful aspects, many national strategies, legal actions and capacity-building activities have been developed and implemented. These efforts work towards the goal of insect diversity conservation in China.     

Natural phosphate doped with KI in HMDS: a mild and efficient reagent for alkylation and glycosylation of nucleobases

Several D-ribonucleosides are prepared from 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranoside and trimethylsilylated nucleobases under mild conditions by using natural phosphate doped with KI as catalyst.     

The crisis in shifting cultivation practices and the promise of agroforestry: a review of the Panamanian experience

Deforestation is proceeding at alarming rates in the Central American Republic of Panama. This is leading to high losses of biodiversity, local wood shortages, increased erosion, and the sedimentation of water bodies. One of the principal causes of deforestation is the expansion of the agricultural frontier through extensive shifting cultivation systems. These land use systems are becoming increasingly unsustainable as populations increase and the amount of agricultural land available declines, and are often associated with low crop productivity, and reduced soil fertility. Agroforestry, or the association of trees with crops and livestock, has the potential of providing both socio-economic and ecological advantages to smallholders. While the number of agroforestry projects has increased dramatically over the past two decades in Panama, there is little information on the impacts these projects have had. This review provides a brief history of agroforestry in Panama, and outlines the current projects underway. In addition, the main factors impeding the increased adoption of agroforestry are examined, and recommendations are provided.     

CD8 Memory Cells Develop Unique DNA Repair Mechanisms Favoring Productive Division

Immune responses are efficient because the rare antigen-specific naïve cells are able to proliferate extensively and accumulate upon antigen stimulation. Moreover, differentiation into memory cells actually increases T cell accumulation, indicating improved productive division in secondary immune responses. These properties raise an important paradox: how T cells may survive the DNA lesions necessarily induced during their extensive division without undergoing transformation. We here present the first data addressing the DNA damage responses (DDRs) of CD8 T cells in vivo during exponential expansion in primary and secondary responses in mice. We show that during exponential division CD8 T cells engage unique DDRs, which are not present in other exponentially dividing cells, in T lymphocytes after UV or X irradiation or in non-metastatic tumor cells. While in other cell types a single DDR pathway is affected, all DDR pathways and cell cycle checkpoints are affected in dividing CD8 T cells. All DDR pathways collapse in secondary responses in the absence of CD4 help. CD8 T cells are driven to compulsive suicidal divisions preventing the propagation of DNA lesions. In contrast, in the presence of CD4 help all the DDR pathways are up regulated, resembling those present in metastatic tumors. However, this up regulation is present only during the expansion phase; i.e., their dependence on antigen stimulation prevents CD8 transformation. These results explain how CD8 T cells maintain genome integrity in spite of their extensive division, and highlight the fundamental role of DDRs in the efficiency of CD8 immune responses.     

Synthesis and Properties of DNA Dumbbells Containing Chemically Active Substituted Pyrophosphate Internucleotide Groups

Abstract

DNA dumbbells with substituted pyrophosphate groups at a definite position of the sugar-phosphate backbone were synthesized by condensation of terminal 5′-phosphomonester- and 3′-methylphosphodiester groups in nicked dumbbells. N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide was used as a condensing agent. An efficient method for producing extended oligonucleotides carrying an O-methyl-substitued 3′-phosphate group was developed. Properties of the modified DNA-dumbbells were investigated. The substituted pyrophosphate group in the DNA dumbbells was efficiently cleaved under the action of N-methylimidazole or ethylendiamine aqueous solutions at pH 8.0.