特异性启动子调控甜瓜ACC氧化酶反义基因载体构建及对烟草的转化

以甜瓜ACC氧化酶反义基因抑制水果成熟过程中内源乙烯的合成为基础,建立甜瓜特异性启动子调控下ACC氧化酶反义基因表达载体。以pCB-ACO1载体为基础,进行平末端连接加入特异性启动子pCAM-ACO1-promoter,对转基因甜瓜表达载体的构建进行特异性启动子的研究,通过叶盘法转化的烟草经过PCR检测已转入含有特异性启动子promoter调控下ACC氧化酶反义基因表达载体,为下一阶段用该反义基因载体转化甜瓜栽培品种奠定基础。     

Fungal deterioration of melon seeds stored in jute sacks and polyethylene bags in Ago-Iwoye,southwestern Nigeria

Laboratory studies were carried out in the Department of Biological Sciences, Ogun State University, Ago-Iwoye, southwestern Nigeria, to determine the extent of fungal deterioration of melon seeds stored in two types of storage bags viz; jute and polyethylene bags. Melon seeds of varieties Tc139 and V2 were stored in jute and polyethylene bags under ambient conditions using the 2 × 2 factorial design (variety vs type of bag) for 12 months. The moisture content (mc), incidence of visible mouldiness (ivm) and germinability of the stored seeds were determined monthly. The mc of Tc139 ranged from 6.1 to 6.7% in jute and 6.2 to 6.5% in polyethylene bags. The ivm which was initially 2.1% increased to 10.7% and 5.5% in jute and polyethylene bags respectively, after 12 months in storage. The germination percentage decreased from 96.3% to 28.7% and 45.3% in jute and polyethylene bags, respectively. The mc of V2 stored in jute and polyethylene bags varied from 5.9 to 6.4%, and 5.8 to 6.2%, respectively. The ivm increased from 1.8% before storage to 8.9% and 4.8% in jute and polyethylene bags, respectively, after 12 months. The percentage seed germination declined from 98.0%to 37.3% in jute and 48.7% in polyethylene bags after 12 months. Decreased incidence of field fungi namely: Alternaria, Botryodiplodia theobromae, Cladosporium, Fusarium and Macrophomina phaseolina was accompanied by simultaneous increase in storage fungi viz: Aspergillus, Penicillium, and Rhizopus with prolonged storage. This revised version was published online in June 2006 with corrections to the Cover Date.     

Bitter taste thresholds, numbers and diameters of circumvallate papillae and their relation with age in a Turkish population

Objectives: This study analyses the relationship between the sense of bitter taste and age. The relationships between these and the numbers and diameters of Circumvallate Papillae (CP) are also analysed. Subjects: Twenty-four elderly subjects (from 65 to 85 years) and 30 young subjects (from 17 to 25 years) were studied. Method: Bitter taste thresholds were determined by the three drop method with an ascending series of concentrations. The numbers and diameters of CP were observed by direct naked eye observation using a wooden tongue depressor, a gauge and a light source. Results: The bitter taste acuity was significantly poorer in the older sample. There was no relationship between the bitter taste acuity and number of papillae but an inverse relationship was observed between the bitter taste acuity and diameters of papillae, thus lower acuity was associated with larger papillae. It was also observed that the diameters of papillae were inversely related to the numbers of CP. The distribution of numbers and diameters of CP were not significantly different between these samples with age.     

Taste sensitivities to PROP and PTC vary independently in mice

Mammals use common mechanisms to detect, transduce and process taste stimulus information. For example, they share families of receptors that respond to amino acids, and sweet- and bitter-tasting stimuli. Nonetheless, it also clear that different species exhibit unique taste sensitivities that may reflect specific genetic variations. In humans, sensitivities to the chemically similar, bitter-tasting compounds 6-n-propylthiouracil (PROP) and phenylthiocarbamide (PTC) are heritable and strongly correlated, suggesting a common genetic basis. However, it is unknown whether PROP and PTC taste sensitivities are similarly correlated in mice. Here we report that PROP and PTC taste sensitivities vary independently between two inbred strains of mice. In brief-access taste tests C3HeB/FeJ (C3) and SWR/J (SW) mice possess similar taste sensitivity to PTC, while SW mice are significantly more sensitive to PROP than are C3 mice. In two-bottle preference tests, however, SW mice display greater aversion to both compounds. This discrepancy may be explained by the observation that SW mice consumed taste solutions at a greater rate during the intake test than did C3 mice. Therefore, PTC avoidance is correlated with the amount of PTC consumed in the intake tests rather than the concentration of PTC tested. These findings suggest that post-ingestive factors play a significant role in PTC avoidance during intake tests and highlight an important advantage of brief-access tests over intake tests in resolving the gustatory and post-ingestive contributions to taste-related behaviors. Most strikingly, these results demonstrate that in mice, unlike in humans, PTC and PROP taste sensitivities vary independently, thereby suggesting a subtle functional diversity of bitter-taste mechanisms across mammalian species.     

Identification of ligands for two human bitter T2R receptors

Earlier, a family of G protein-coupled receptors, termed T2Rs, was identified in the rodent and human genomes through data mining. It was suggested that these receptors mediate bitter taste perception. Analysis of the human genome revealed that the hT2R family is composed of 25 members. However, bitter ligands have been identified for only three human receptors so far. Here we report identification of two novel ligand-receptor pairs. hT2R61 is activated by 6-nitrosaccharin, a bitter derivative of saccharin. hT2R44 is activated by denatonium and 6-nitrosaccharin. Activation profiles for these receptors correlate with psychophysical data determined for the bitter compounds in human studies. Functional analysis of hT2R chimeras allowed us to identify residues in extracellular loops critical for receptor activation by ligands. The discovery of two novel bitter ligand-receptor pairs provides additional support for the hypothesis that hT2Rs mediate a bitter taste response in humans.     

Phylogenetic relationships among Cucumis species based on the ribosomal internal transcribed spacer sequence and microsatellite markers

The phylogenetic relationships within the genus Cucumis (a total of 25 accessions belonging to 17 species) were studied using the nuclear ribosomal DNA internal transcribed spacer (ITS) region. The analysis included commercially important species such as melon (C. melo L.) and cucumber (C. sativus). Two additional cucurbit species, watermelon and zucchini, were also included as outgroups. The data obtained reflected the clustering of Cucumis species in four main groups, comprising accessions from cucumber, melon, C. metuliferus and the wild African species. Some of the species clustered in different positions from those reported in classifications previously described by other authors. The data obtained clearly identify a division between the 2n=2x = 14 species (C. sativus) and the 2n = 2x = 24 ones (C. melo and wild species). Within the wild species we identified a subgroup that included C. sagittatus and C. globosus. Oreosyce africana, also classified as Cucumis membranifolius, was shown to be nested within Cucumis. Three accessions previously classified as independent species were shown to be genotypes of Cucumis melo. A set of melon and cucumber SSRs were also used to analyse the Cucumis species and the results were compared with the ITS data. The differential amplification of the SSRs among the accessions made it possible to distinguish three main groups: melon, cucumber and the wild species, though with less detail than applying ITS. Some SSRs were shown to be specific for melon, but other SSRs were useful for producing PCR fragments in all species of the genus.We are grateful to NCRPIS, IPK in Gatersleben, Semillas Fitó S.A., Michel Pitrat and Fernando Nuez for providing seeds. We would also like to thank Vanessa Alfaro, Trinidad Martínez and Núria Galofré for their excellent technical assistance. This work was financed by project AGL2000-0360 of Spains Ministerio de Ciencia y Tecnología (MCYT). AJMs work was supported by a postdoctoral contract from Spains MCYT.     

The contribution of taste bud populations to bitter avoidance in mouse strains differentially sensitive to sucrose octa-acetate and quinine

Mice of the SWR/J (SW) strain avoid orally delivered sucrose octa-acetate (SOA), whereas the mice of the C3HeB/FeJ (C3) strain are insensitive to SOA. Mice of both strains and of a congenic strain (C3.SW) that shares more than 99% of the C3 genome, were tested in a taste-salient brief-access taste test for responses to SOA and quinine hydrochloride, before and after transection of the glossopharyngeal or chorda tympani nerve, or sham surgery. Prior to surgery, congenic SOA tasters (C3.SW(T)) were phenotypically identical to the SW strain in avoidance of SOA, but showed a greater reduction in sensitivity after nerve transection. For quinine avoidance, which is thought to be a polygenic trait, SW mice showed the greatest sensitivity to quinine, C3 the least and C3.SW(T) mice were different from both parental strains, showing intermediate sensitivity. Nerve transections had only a moderate effect on quinine sensitivity, suggesting that both anterior and posterior taste bud fields contribute to behavioral quinine avoidance. These findings are discussed with regard to the distribution in the oral cavity of putative taste receptors for quinine and SOA and the peripheral organization of bitter taste.     

Feeding rates and carbohydrate metabolism by Bemisia tabaci (Homoptera: Aleyrodidae) on different quality phloem saps

Abstract.The effects of water stress on phloem sap quality of the melon, Cucumis melo, and how this, in turn, has an impact on the sweet potato whitefly, Bemisia tabaci were studied. Melon plants were grown under watering regimes that produced plants with or without water stress. Plants showed strong developmental responses to the treatments; water-stressed plants were shorter, with fewer, smaller leaves than those without stress. There was, however, no effect of plant water stress on the development period of whiteflies feeding on these plants, or on the weights of male or female adults. Honeydew production was used as an indirect measure to test whether the absence of insect developmental or behavioural effects was due to differential phloem sap ingestion. Feeding rates on the stressed plants were almost half those on unstressed plants, and there was also variation in the daily pattern of honeydew production. Phloem sap and honeydew were analysed to determine why the feeding behaviours differed. Amino acid composition of the phloem sap was similar in both groups of plants, but carbohydrate concentrations were greater in water-stressed plants, indicating that lower feeding rates may have been due either to the physical or nutritional quality of the phloem sap. The honeydew of insects that were feeding on water-stressed plants contained a greater concentration of carbohydrate than those on unstressed plants, and was composed of a significantly greater proportion of glucose and the disaccharide, trehalulose. This isomerization of more complex sugars from those in the diet suggests that B. tabaci uses a mechanism of osmoregulation to actively maintain its internal water status. It is concluded that transient conditions of water stress in this host plant do not affect the development of B. tabaci, due to physiological and behavioural changes in response to diets with different nutritional and physical properties. The implications of this finding for the feeding biology of B. tabaci on desert-grown crops are discussed.     

Physiological activities and the active constituents of potentially medicinal plants used by wild chimpanzees of the Mahale mountains,Tanzania

Potential medicinal plants for wild chimpanzees have been studied in order to discover their physiologically active compounds. Tests of the physiological activity of 3 plant species—Vernonia amygdalina, Aspilia mossambicensis, andFicus exasperata—indicate that they contain a variety of active compounds. From one species,V. amygdalina, an antitumor agent and 2 possible antitumor promoters are identified. Furthermore, steroid glucosides were isolated as the bitter substances. These structurally new compounds are expected to exhibit a number of significant physiological activities. The chemical investigation of possible medicinal plants used by chimpanzees should be helpful in recovering naturally occurring compounds of medicinal significance for human use.