Spontaneous Phloem bleeding from cryopunctured fruits of a ureide-producing legume

The vasculature of the dorsal suture of cowpea (Vigna unguiculata [L.] Walp) fruits bled a sugar-rich exudate when punctured with a fine needle previously cooled in liquid N₂. Bleeding continued for many days at rates equivalent to 10% of the estimated current sugar intake of the fruit. A phloem origin for the exudate was suggested from its high levels (0.4-0.8 millimoles per milliliter) of sugar (98% of this as sucrose) and its high K⁺ content and high ratio of Mg²⁺ to Ca²⁺. Fruit cryopuncture sap became labeled with ¹⁴C following feeding of [¹⁴C]urea to leaves or adjacent walls of the fruit, of ¹⁴CO₂ to the pod gas space, and of [¹⁴C] asparagine or [¹⁴C]allantoin to leaflets or cut shoots through the xylem. Rates of translocation of ¹⁴C-assimilates from a fed leaf to the puncture site on a subtended fruit were 21 to 38 centimeters per hour. Analysis of ¹⁴C distribution in phloem sap suggested that [¹⁴C]allantoin was metabolized to a greater extent in its passage to the fruit than was [¹⁴C] asparagine. Amino acid:ureide:nitrate ratios (nitrogen weight basis) of NO₃-fed, non-nodulated plants were 20:2:78 in root bleeding xylem sap versus 90:10:0.1 for fruit phloem sap, suggesting that the shoot utilized NO₃-nitrogen to synthesize amino acids prior to phloem transfer of nitrogen to the fruit. Feeding of ¹⁵NO₃ to roots substantiated this conclusion. The amino acid:ureide ratio (nitrogen weight basis) of root xylem sap of symbiotic plants was 23:77 versus 89:11 for corresponding fruit phloem sap indicating intense metabolic transfer of ureide-nitrogen to amino acids by vegetative parts of the plant.     

Biochemical and genetic characterization of three hamster cell mutants resistant to diphtheria toxin

We describe here three different hamster cell mutants which are resistant to diphtheria toxin and which provide models for investigating some of the functions required by the toxin inactivates elongation factor 2 (EF-2). Cell-free extracts from mutants Dtx(r)-3 was codominant. The evidence suggests that the codominant phenotype is the result of a mutation in a gene coding for EF-2. The recessive phenotype might arise by alteration of an enzyme which modifies the structure of EF-2 so that it becomes a substrate for reaction with the toxin. Another mutant, Dtx(r)-2, contained EF-2 that was sensitive to the toxin and this phenotype was recessive. Pseudomonas aeruginosa exotoxin is known to inactivate EF-2 as does diphtheria toxin and we tested the mutants for cross-resistance to pseudomonas exotoxin. Dtx(r)-1 and Dtx(r)-3 were cross-resistant while Dtx(r)-2 was not. It is known that diphtheria toxin does not penetrate to the cytoplasm of mouse cells and that these cell have a naturally occurring phenotype of diphtheria toxin resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance of the hybrid cells to diphtheria toxin. Intraspecies hybrids containing the genome of mutants Dtx(r)-1 and Dtx(r)-3 had some resistance while those formed with Dtx(r)-2 were as sensitive as hybrids derived from fusions between wild-type hamster cells and mouse 3T3 cells.     

Uptake and Utilization of Xylem-borne Amino Compounds by Shoot Organs of a Legume

Amino compounds representative of the major N solutes of xylem sap were pulse-fed (10 to 20 minutes) singly in ¹⁴C-labeled form to cut transpiring shoots of white lupin (Lupinus albus L.). ¹⁴C distribution was studied by autoradiography and radioassays of phloem sap, leaflet tissues, and shoot parts harvested at intervals after labeling. Primary distribution of N by xylem was simulated using a 20-minute labeling pulse followed by a 30-minute chase in unlabeled xylem sap. Shoots fed ¹⁴C-labeled asparagine, glutamine, valine, serine, or arginine showed intense labeling of leaflet veins and marked retention (35 to 78%) of ¹⁴C by stem + petioles. Shoots fed ¹⁴C-labeled aspartic acid or glutamic acid showed heaviest ¹⁴C accumulation in interveinal regions of leaflets and low uptake (11 to 20%) of ¹⁴C by stem + petioles. Departing leaf traces were major sites of uptake of all amino compounds, and the implications of this were evaluated. Fruits acquired only 1 to 5% of the fed label directly from xylem, but more than doubled their intake during the period 30 to 160 minutes after feeding through receipt of ¹⁴C transferred from xylem to phloem in stem and leaves. ¹⁴C-Labeled asparagine and valine transferred directly from xylem to phloem, but the ¹⁴C of ¹⁴C-labeled aspartic acid and arginine appeared in phloem mainly as metabolic products of the fed compound. The labeling of the soluble pool of leaflets reflected these differences. The significance of heterogeneity in distribution and metabolism of xylem amino compounds in the shoot was discussed.     

Photosynthetic Pod Wall of Pea (Pisum sativum L.): Distribution of Carbon Dioxide-fixing Enzymes in Relation to Pod Structure

The pod wall of pea (Pisum sativum L.) was shown to contain two distinct photosynthetic layers. The outer, comprising chlorenchyma of the mesocarp, captured CO₂ from the outside atmosphere; the inner, a chloroplast-containing epidermis lining the pod gas cavity, was involved in photoassimilation of the CO₂ released from respiring seeds.     

Asparagine metabolism-key to the nitrogen nutrition of developing legume seeds

Asparagine accounted for 50 to 70% of the nitrogen carried in translocatory channels serving fruit and seed of white lupin (Lupinus albus L.). Rates of supply of the amide always greatly exceeded its incorporation as such into protein. An asparaginase (l-asparagine amido hydrolase EC 3.5.1.1) was demonstrated in crude extracts of seeds. In vitro activity was up to 5 mumoles of aspartate formed per hour per gram fresh weight at the apparent Km(Asn) value of 10 mM, and this more than accounted for the estimated rates of asparagine utilization in vivo. Asparaginase activity per seed increased 10-fold in the period 5 to 7 weeks after anthesis, coinciding with early stages of storage protein synthesis in the cotyledons.Double labeled ((14)C (U), (15)N (amide)) asparagine was fed to fruiting shoots through the transpiration steram. Fruit phloem sap analysis indicated that virtually all of the label was translocated to seeds in the form of asparagine. In young seeds (15)N from asparagine breakdown was traced to the ammonia, glutamine, and alanine of endospermic fluid, the (14)C appearing mainly in nonamino compounds. In the cotyledon-filling stage the C and N of asparagine was contributed to a variety of amino acid residues of protein.     

The organizer region and pattern regulation in amphibian embryos

The cellular proportions in the dorsal-to-ventral, mesodermal sequence of pattern elements in the gastrula of certain amphibian embryos regulate with respect to embryo size. The dorsal, blastoporal lip serves as an organizer for this developmental sequence and the grafting of an additional organizer into a ventral location results in a symmetric pattern of cell types. A size-regulating, reaction-diffusion model is presented which produces positional information for development consistent with experimental observations in normal amphibian development and in the presence of an additional, ventrally-located, organizer region.     

荷叶离褶伞子实体化学成分

本文对祁连山野生荷叶离褶伞Lyophyllum decastes子实体的化学成分和生物活性进行研究。采用硅胶色谱、高效液相色谱等多种方法进行分离纯化得到8个化合物,通过MS、NMR和电子圆二色谱 （ECD）等方法确定了化学结构,其中有4个为聚炔类化合物。化合物1作为天然产物系首次报道,其相绝对构型是通过比较ECD的方法确定。对所得聚炔类化合物应用细胞模型进行抗氧化活性（CAA）指标检测,化合物1-4均呈现一定抗氧化活性,其中化合物1的抗氧化活性最强,其EC₅₀为(24.73±6.12)μmol/L。聚炔类化合物1-4为荷叶离褶伞首次报道成分,可作为祁连山野生荷叶离褶伞HPLC-DAD化学表征参考化合物。     

利用APSIM模型分析不同播期和耕作方式对旱地小麦籽粒干物质积累的影响

黄土丘陵区旱地小麦籽粒干物质积累的准确模拟可为调控小麦生产提供重要的技术支持。本研究利用甘肃省定西市安定区1971—2017年的气象资料和甘肃省定西市安定区凤翔镇安家沟村2016—2017年的大田试验数据,基于APSIM模型对旱地小麦籽粒干物质积累与分配进行模拟,并在模型验证的基础上,定量分析了播期和耕作方式对小麦籽粒干物质积累的影响。结果表明: 3个播期(早播、正常播、晚播)和4种耕作方式(传统耕作、传统耕作+覆盖、免耕、免耕+覆盖)下,籽粒干物质模拟值与实测值间的均方根误差(RMSE)为57.5～143.1 kg·hm^-2,归一化均方根误差(NRMSE)为1.4%～9.9%,模型模拟精度较高。不同播期下,耕作方式对籽粒干物质积累的促进效果排序均表现为: 免耕+覆盖>传统耕作+覆盖>免耕>传统耕作,免耕+覆盖最有利于小麦籽粒干物质积累,而免耕与传统耕作差异不显著。不同耕作方式下,小麦干物质积累过程均表现为早播好于正常播和晚播,晚播对干物质积累的影响较大,积累过程最不理想。