A study of conduction velocity in nonmyelinated nerve fibers.

By treating a nonmyelinated nerve fiber as a continuous cable consisting of three distinct zones (Resting, transitional, and excited), the following mathematical expression was derived: (formula: see text) where v is the conduction velocity, d the diameter of the fiber, R the resistance of the membrane of unit area at the peak of excitation, rho the resistivity of the medium inside the fiber, and C the capacity of membrane per unit area. The validity of this expression was demonstrated by using squid giant nerve fibers intracellularly perfused with dilute salt solutions. The relationship between these results and previous theories and experiments on conduction velocity is discussed.     

Microtubules inside the plasma membrane of squid giant axons and their possible physiological function

Summary The effects of application of the microtubule-disassembling reagents to squid giant axons upon resting potential, the height of the propagated action potential, and the threshold to evoke action potential were studied using colchicine, podophyllotoxin, vinblastine, griseofulvin, sulfhydryl reagents including NEM, diamide, DTNB and PCMB, and Ca²⁺ ions. At the same time, the effects of concentrations of K halides and K glutamate on the above physiological properties were studied in comparison within vitro characteristics of microtubule assembly from purified axoplasmic tubulin.It was found that there was good correlation between conditions supporting maintenance of membrane excitability and microtubule assembly. The experiments suggest that associated with the internal surface of the plasma membrane there are microtubules which regulate in part both resting and action potentials.     

Relationship between hormone content and autonomy in various autonomous tobacco cells cultured in suspension

Various autonomous cultured tobacco cells including crown gallwere examined for their contents of growth regulators by meansof Avena curvature test, cell-division induction test, and tobaccopith callus test. The crown gall cells derived from cv. Hicks produced auxin andcytokinin in the high levels of 300–500 µg IAA equivalentsand 40–80 µg kinetin equivalents per kg, respectively.The major auxin was identified as indole-3-acetic acid basedon mass spectrometry and gas chromatography. These cells alsoproduced methyl indole-3-acetate as a minor component. One ofthe cytokinins was identified as ribosyl-trans-zeatin by meansof both gas chromatography-mass spectrometry and high performanceliquid chromatography. Auxin and cytokinin activities were not detected in the followingthree suspension cultured tobacco cells: cells requiring neithercytokinin nor auxin derived from the callus of N. tabacum cv.Bright Yellow and cells requiring auxin but not cytokinin derivedfrom the calluses of cv. Bright Yellow and cv. Hicks. Theirauxin and cytokinin contents per kg were less than 1 µgIAA equivalent and less than 0.1 µg kinetin equivalent,respectively. The results obtained in this study indicate that enhanced hormonalcontent is not the only reason for autonomous growth. (Received August 16, 1979; )     

Two distinct intervening sequences in different ribosomal DNA repeat units of Sciara coprophila.

We have prepared a partial gene library of sheared DNA from the fungus fly, Sciara coprophila, by dA-T tailing and insertion into pBR322. Two ribosomal DNA clones which differ from the usual ribosomal DNA organization in this organism were studied in detail. Clone pBc 1L-1 has an intervening sequence of 1.4 kb, and clone pBc 6D-6 has an intervening sequence of 0.9 kb. These intervening sequences occur in about the same position in 28S rDNA, but do not appear to share sequence homology with one another. Previously we found that 90% of Sciara ribosomal DNA is homogenous and lacks an intervening sequence, and our present data explains the size heterogeneity found in most of the remaining 10%. We have found no evidence of size heterogeneity in the nontranscribed spacer.     

Clinical isolate of Pseudomonas aeruginosa that degrades salicylate by the ortho pathway

A clinical isolate of Pseudomonas aeruginosa was found capable of utilizing salicylate by the salicylate hydroxylase and beta-ketoadipate pathway.     

Mutagenic activity of amino acid pyrolyzates in Salmonella typhimurium TA 98.

Pyrolyzates of 25 amino acids and 5 indole derivatives were tested for mutagenicity in the histidine-requiring mutant Salmonella typhimurium TA 98. Significant mutagenic activity was detected with pyrolyzates of most of the amino acids. These pyrolyzates required a liver microsomal fraction, as representative of mammalian metabolism, to be detected as mutagens. Among the pyrolyzates tested, the highest mutagenic activity was observed with that of L-tryptophan. As little as 10 microgram of the pyrolyzate of L-tryptophan had detectable mutagenic activity toward TA 98. The optimal pyrolysis temperatures for the formation of mutagenic products were shown to be 500 degrees C for L-tryptophan and 600 degrees C for the other amino acids. The results from pyrolyses of some indole derivatives suggest that an amino group at the alpha-position to the carboxyl group of L-tryptophan plays an important role in the formation of mutagens.     

Binding of aluminium to DNA of DNP in pea root nuclei

The association of absorbed aluminium (Al) with nuclei in Alaskapea roots was shown by zonal centrifugation of isolated nuclei.In nuclei, 73% of the total incorporated Al was detected inthe DNP fraction. Furthermore, Al in DNP was found to be boundspecifically to DNA by gel filtration of dissociated DNP. (Received March 19, 1977; )     

Effect of auxins on the formation of ubiquinone by tobacco plant cells in suspension culture

Ubiquinone (UQ) formation in BY-2 tobacco cells was especially promoted by a high concentration of 2,4-D. 2,4,5-T, MCP and NAA also promoted UQ formation in these cells. The UQ content in the cells cultured at high concentrations of 2,4-D was higher than that of controls throughout the culture period. The addition of 2,4-D at an early period in cell growth was very effective in promoting UQ formation, but addition at the stationary phase was ineffective. Cell growth was improved by adding phosphate to the medium but UQ content was decreased. UQ content decreased slowly during subculturing, whereas cell growth recovered gradually.