Fused cells of frog proximal tubule: I. Basic membrane properties

Summary Patch-clamp techniques were used to study a K channel in the cell membrane of MDCK cells. This cell line derives from the kidney of a normal dog, presumably from the distal nephron, a region involved in potassium secretion. The cells were cultured in confluent monolayers and approached from the apical side. The K channel we describe is Ca²⁺ and voltage activated, has a conductance of 221±7 pS, and can be inhibited by 10mm tetraethylammonium and by 1mm quinidine, but not by 4-aminopyridine, nor by 1mm Ba²⁺ added to the outer side. Using the whole-cell configuration, we find that most of the cationic conductance of the membrane is constituted by a K-specific one (maximum K conductance 32.1±3.9 nSvs. a leak conductance of 1.01±0.17 nS). Comparisons of the maximum K conductance with that of a single K channel indicates that an MDCK cell has an average of 145 such channels. The membrane capacity is 24.5±1.4 pF.     

Cloning and sequencing of the Escherichia coli gyrA gene coding for the A subunit of DNA gyrase

The gene gyrA of Escherichia coli, which encodes the A subunit of DNA gyrase (topoisomerase II), has been cloned and a region of approximately 3300 base-pairs sequenced. An open reading frame of 2625 nucleotides coding for a protein of 97,000 Mr is located. The peptide weight of the subunit predicted from this open reading frame is in close agreement with previously published estimates of that of the A subunit. There is a "TATAAT" promoter motif located 44 bases upstream from the first "ATG" of the open reading frame. The amino acid sequence derived from the nucleotide sequence is about 50% homologous with that derived from the Bacillus subtilis gyrA gene sequence, with several regions showing greater than 90% homology.     

Influence of microgravity on cellular differentiation in root caps of Zea mays

We launched imbibed seeds of Zea mays into outer space aboard the space shuttle Columbia to determine the influence of microgravity on cellular differentiation in root caps. The influence of microgravity varied with different stages of cellular differentiation. Overall, microgravity tended to 1) increase relative volumes of hyaloplasm and lipid bodies, 2) decrease the relative volumes of plastids, mitochondria, dictyosomes, and the vacuome, and 3) exert no influence on the relative volume of nuclei in cells comprising the root cap. The reduced allocation of dictyosomal volume in peripheral cells of flight-grown seedlings correlated positively with their secretion of significantly less mucilage than peripheral cells of Earth-grown seedlings. These results indicate that 1) microgravity alters the patterns of cellular differentiation and structures of all cell types comprising the root cap, and 2) the influence of microgravity on cellular differentiation in root caps of Zea mays is organelle specific.     

兜兰胚胎学的研究

云南兜兰花药壁有五层细胞,绒毡层细胞具双核,属分泌型。小孢子母细胞减数分裂为同时型。四分体中四个小孢子呈四面体或左右对称式排列。成熟花粉为二细胞型。单粒分散的花粉包裹于黄色粘性物质中。生殖细胞最初形成的壁为胼胝质的,待游离到营养细胞质中时,具一层很薄的 PAS 正反应的壁,直到花药开裂时这层壁仍存在。成熟花粉无特化的萌发孔,只具薄壁区。胚珠为薄珠心,具一层珠被,胚囊发育为葱型,成熟胚囊为6—8核,胚发育过程中,具2—4细胞胚柄。胚乳具二核。种子成熟时胚柄及胚乳核都消失。成熟种子只具单层细胞的种皮和一个未分化的球形胚。     

三尖杉属受精作用的研究

三尖杉属的精原细胞有一类似银杏生毛体的星状体结构,它分裂产生的2个精子,在大小与形态上都基本相同,而且在精子细胞质中具有拟核仁颗粒存在。上述结构是三尖杉属的重要特点之一。本属植物的成熟卵细胞特别长,细胞质中有丰富的拟核仁结构,卵核下方具2—3团浓稠的细胞质团,这些结构很像穗花杉的卵细胞。三尖杉属的受精作用,属于有丝分裂后类型,这种类型只在松科和三尖杉科中发现。受精后,卵细胞发生强烈的极性分化,上部细胞质变成高度液泡化;相反,下部细胞质则聚集大量蛋白泡和拟核仁颗粒。     

高等植物花粉母细胞内肌动蛋白的聚丙烯酰胺凝胶电泳分析

采用聚丙烯酰胺凝胶电泳技术分析了黑麦、蚕豆和百合花粉母细胞内肌动蛋白的存在与动态,结果表明高等植物的花粉母细胞在细胞融合期内的确存在一定量的肌动蛋白,并且,这种蛋白在早偶线期时出现,到四分体时期后消失。文章讨论了肌动蛋白的存在及其与细胞融合现象的联系。     

扁苞蕗蕨和长柄蕗蕨的细胞分类学研究

本文首次报道了四川产扁苞蕗蕨和长柄蕗蕨的染色体及孢子发生情况。它们的染色体数目分别为 n=26和n=28,都是有性生殖的二倍体。染色体基数26在蕗蕨属的发现进一步证明了它和膜蕨属、厚壁蕨属的密切亲缘关系。这两种蕗蕨的孢子囊通常形成128个孢子及少数256个孢子的情况被描述,它们应该被看成是有性生殖真蕨,尤其是在膜蕨科和薄囊真蕨中的其他较原始的类群中的正常的孢子发生路线。     

Effect of paclobutrazol on accumulation of organic acids and total phenols in apple wood

Apple trees (Malus domestica Borkh Spartan grafted on MM 106 rootstock) planted in 1976 in an orchard at Beltsville, Maryland, were treated with paclobutrazol (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-1,2,4-triazol-1-yl-pentan-3-ol) using a foliage spray in 1982 and by trunk banding in 1983. Paclobutrazol did not inhibit shoot growth in 1983; however, shoot growth was significantly retarded in 1984. Increases in organic acids, including succinic, malic, citric, and quinic, and also in total phenols, occurred in wood produced in 1983 on paclobutrazol-treated trees when growth was not inhibited and in wood produced in 1984 when growth was inhibited. The organic acid content of both paclobutrazol-treated and untreated wood tended to decrease from the winter dormant period through growth resumption in the spring. However, the content of total phenols remained nearly the same throughout this sampling period.Mention of a trademark, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Metabolic changes associated with bud break induced by thidiazuron

Bud break in apple (Golden Delicious,Malus domestica Borkh) was induced by thidiazuron (N-phenyl-N-1,2,3-thidiazol-5-ylurea). In control and thidiazuron-treated shoots, higher amounts of soluble carbohydrates (sorbitol, fructose, glucose, sucrose) and galacturonic acid were found in the phloem, but higher amounts of starch and cell wall polysaccharides, including cellulose and xylose, were found in the xylem. A decrease in soluble carbohydrates and starch in both phloem and xylem was associated with induction of bud break by thidiazuron. However, little change in cell wall polysaccharides was found. Total carbohydrates were higher in the upper than in the lower portion of shoots. The breaking of dormancy by thidiazuron was also associated with an increase in organic acid content and respiration in buds. KCN inhibited bud respiration during all stages of development. Organic acid content was inversely related to carbohydrate content in developing buds. Axes contained more carbohydrates and organic acids than did scales.     

Sequence dependent conformations of oligomeric DNA's in aqueous solutions and in crystals

In order to determine the sequence dependence of the conformation of deoxynucleotides, Raman spectra have been obtained for the following oligodeoxynucleotides in aqueous salt solutions and in crystals: d(CpG)(I), d(TGCGCGCA)(II), d(CACGCGTG)(III), d(CGTGCACG)(IV), d(CGCATGCG)(V), d(ACGCGCGT)(VI), d(CGCGTACGCG)(VII), d(CGCACGTGCG)(VIII) and d(CGTGCGCACG)(IX), d(GCTATAGC) (X), d(GCATATGC) (XI), d(GGTATACC) (XII) and d(GGATATCC) (XIII). The normal B type conformation is observed for all the oligomer DNA's at low salt (0.1-1.0 M NaCl) concentration in the temperature range of 0-25 degrees C. It was considered possible that all of the first nine oligomers could go into the Z form in aqueous high salt (5.0-6.0 M NaCl) solutions, and under these conditions the last four were considered candidates to go into the A form. The B-type conformation was found to exist in high salt solutions for (I), (IV), (V), (VI), (X), (XI) and (XIII); the Z or partial Z conformation appears in high salt solution for the oligomers, (II), (III), (VII), (VIII) and (IX); an A or partial A conformation appears in high salt solution for (XII). In the crystalline state, (IV), (VIII), (X), and (XI) stay in the B-form and all of the other oligomers adopt the complete Z-form except for (XII) which crystallizes in the A form. In both the crystal and in aqueous solutions, the identification of the conformation genus was made by means of Raman spectroscopy. In the crystal of (I), grown at pH7.0, guanosine is found to be in C3'-endo/syn conformation and cytidine in C2'-endo/anti, which may be taken as the ideal building block of the typical Z conformation. At pH4, (I) crystallizes in a conformation similar to the B genus. A study of the thermally induced B to Z transition has been carried out for (II) and (III). Based on the analysis of Raman spectra of the alternating pyrimidine-purine oligomers which might be expected to go into the Z form, the tendency for these oligonucleotides to adopt the Z form can be ranked as: d(CGCGCGCG) greater than (II) greater than (III) greater than (V) approximately (VI) greater than (IV) for octamers and (VII) greater than (VIII) greater than (IX) for the decamers. Similarly, those oligomers which might have a tendency to go into the A form could be ranked as (XII) greater than (XIII) approximately (X) greater than (XI). These data should provide help in formulating rules for predicting the sequence dependence of the B to A and B to Z transitions. Some possible rules are explored, but precautions should be taken.