Stereoselective total synthesis of ceramide Di-, Tri- and tetrahexosides of wheat flour

The first total synthesis of glycosphingolipids isolated from wheat flour has been achieved in a regio- and stereo-controlled manner.Abbreviations THF tetrahydrofuran - DMF dimethylformamide Part 53 in the series Synthetic Studies on Cell Surface Glycans     

Construction and properties of a chimeric bacteriophage lysis gene

Abstract The genomes of DNA phage ΦX174 and of RNA phage MS2 each encode a single lysis protein, E protein and L protein, respectively. Based on the known DNA and protein sequences, and with the aid of structural predictions of the proteins, a chimeric gene was constructed. The resulting protein was composed of the N-terminal sequence of E protein and the C-terminal sequence of L protein. The truncated E and L polypeptides used in this construction were functionally inactive. However, the chimeric gene product had very high lysis-inducing activity. This construction is an example which could be extended to the engineering of other lysis proteins designed with specific biotechnological processes in mind.     

红树林植物海滨猫尾木在我国首次发现

红树林是发育于热带海岸潮间带的一种特殊的木本植物群落。据最近的报道补,我国南部沿海红树林的组成种类(包括半红树林成分)有卤蔽科、千屈菜科、海桑科、玉蕊科、使君子科、红树科、梧桐科、锦葵科、大戟科、糠科、紫金牛科、夹竹桃科、茜草科、爵床科·、马鞭草科、棕搁科等,共16科,20属,31种。最近我们通过海岸带植物调查和海南岛珍稀、濒危植物种类调查,首次发现了紫威科的海滨猫尾木的分布。现将其形态特征、分布和生态学特性简报于下: 海澳猫尾木(新拟)图 Dolichandrone spathaeae(L.f.)K.Sehum.,FI.Kais.Wilh.123.1889;Merr.F 1…     

Transgenic tobacco resistant to a bacterial disease by the detoxification of a pathogenic toxin

Summary Some plant pathogens produce toxins which cause disease in infected plants. One of the pathogenic toxins, tabtoxin, is produced by Pseudomonas syringae pv. tabaci, which causes wildfire of tobacco. A tabtoxin resistance gene (ttr) coding for an acetyltransferase isolated from Pseudomonas syringae pv. tabaci was fused to the 35S promoter of the cauliflower mosaic virus (CaMV) to construct a chimeric gene for introduction into tobacco cells by Agrobacterium-mediated transformation. The transgenic tobacco plants showed high specific-expression of the ttr gene and no chlorotic symptoms caused by tabtoxin treatment or with infection by Pseudomonas syringae pv. tabaci. These results demonstrate a successful approach to obtain disease-resistant plants by detoxification of the pathogenic toxins which play an important role in pathogenesis.     

The growth and asymmetry of neighbouring plants of white clover (Trifolium repens L.)

Summary Transplants of white clover (Trifolium repens L.) were grown isolated from each other and in pairs placed at different distances apart. The paired plants developed asymmetrically and at the interface between paired clones both the density of nodes and of stolons appeared to reach ceiling values that were of the same order as those achieved in isolated clones. It is argued that the growth of plants of T. repens is controlled by the local conditions experienced by the plant parts and not by integrated growth of the whole. Transplants of three different genotypes of T. repens, which differed in growth form, were grown as neighbouring pairs and the calculated asymmetry of the plants was used to compare their mutual aggressivenes. The more compact (phalangeal) genotypes induced greater asymmetry in their neighbours than the more diffuse forms.     

Comparative study of the composition of waxes extracted from isolated leaf cuticles and from whole leaves of Citrus: Evidence for selective extraction

The effect of different extraction methods on the composition of samples of soluble cuticular lipids (SCL) of Citrus aurantium L. was investigated. The variation of extraction yields, when whole leaves were immersed in solvent, was studied as a function of solvent type and duration of immersion. Cuticular waxes were also quantitatively extracted from isolated cuticular membranes of C. aurantium and their composition was compared to that of samples obtained by the immersion method. Significant differences were observed. Higher carbon number homologues of the aliphatic constituent classes were discriminated against when whole C. aurantium leaves were extracted by immersion. The alkyl ester fraction was almost entirely lacking in extracts from whole leaves. The dependence on carbon chain length of the saturation concentrations in chloroform of major aliphatic SCL constituents was determined. The results are discussed in terms of the major physico-chemical processes involved in the extraction of SCL.     

Water use efficiency as a function of leaf age and position within the cotton canopy

The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention in recent years. However, insufficient information exists on the coordination of transpiration and CO₂ uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration (E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO₂ mmol⁻¹ H₂O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in stomatal conductance (g_s·H₂O) since decreases in g_s·H₂O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these findings are presented in relation to light competition within the plant canopy during development.     

Citrus replant problem in Iraq II. Possible role of allelopathy

The role of allelopathy in citrus replant problems was investigated in Iraq. The failure of citrus seedlings to grow normally in old citrus orchards was not caused by differences between old and non-citrus soils in electrical conductivity, pH, organic matter, soil texture and those minerals tested. Extracts of soil collected from old citrus orchards significantly reduced the growth of sour orange seedlings. Extracts and decaying sour orange roots reduced the growth of sour orange seedlings as did extracts of non-senescent sour orange leaves and decaying senescent leaves. Thus it appears that allelopathy is at least partly involved in the citrus replant problem.     

Rate of trypanosome killing by lectins in midguts of different species and strains of Glossina

The activity of lectins in different species of tsetse was compared in vivo by the time taken to remove all trypanosomes from the midgut following an infective feed and in vitro by agglutination tests. Teneral male Glossina pallidipes Austen, G. austeni Newstead and G. p. palpalis R-D. removed 50% of all Trypanosoma brucei rhodesiense Stephens & Fantham infections within 60 h. A 'refractory' line of G. m. morsitans Westwood took 170 h to kill 50% infections while a 'susceptible' line of the same species failed to kill 50%. Agglutination tests with midgut homogenates showed differences between fly stocks which accorded with differences in rate of trypanosome killing in vivo. Flies fed before an infective feed were able to remove trypanosomes from their midguts more quickly than flies infected as tenerals. Increasing the period of starvation before infection increased the susceptibility to trypanosome infection of non-teneral flies. Teneral flies showed little agglutinating activity in vitro, suggesting that lectin is produced in response to the bloodmeal. Feeding flies before infection also abolished the differences in rate of trypanosome killing found between teneral 'susceptible' and 'refractory' G. m. morsitans, suggesting that maternally inherited susceptibility to trypanosome infection is a phenomenon limited to teneral flies. Electron micrographs of midguts of G. m. morsitans suggest that procyclic trypanosomes are killed by cell lysis, presumably the result of membrane damage caused by lectin action.     

Endophage-ectophage ratios and plant defense

Summary Endophagous folivores, which are concealed inside leaf tissue for much of their life cycle, or which live externally but feed internally, should be more successful on heavily defended plants than ectophagous species. This is because endophages are more facile at feeding selectively and can manipulate tissue development to avoid physical and chemical defenses and to enhance nutrition. As a result, endophage-ectophage ratios should increase on more heavily defended hosts. This pattern will likely be strengthened by negative asymmetrical interactions with ectophages and pathogens, which may displace endophages from lightly defended hosts. The hypothesis predicts that endophages should be particularly abundant in resource-poor habitats which seem to support a preponderance of heavily defended hosts. Although data do not yet exist for a rigorous test, several observed cases where endophage distributions seem biased toward heavily defended hosts are at least consistent with the hypothesis. Plant defense levels may have little influence on the total number of herbivores associated with a host, but I suggest that guild structure can be profoundly altered.