DNA sequence analysis of point mutations in traA, the F pilin gene, reveal two domains involved in F-specific bacteriophage attachment

Summary Six missense point mutations in traA (WPFL43,44,45,46,47 and 51), the gene encoding F pilin in the transfer region of the F plasmid, have been characterized for their effect on the transfer ability, bacteriophage (R17, QB and fl) sensitivity and levels of piliation expressed by the plasmid. The sequence analysis of the first five of these mutations revealed two domains in the F pilin subunit exposed on the surface of the F pilus which mediate phage attachment. These two domains include residues 14–17 (approximately) and the last few residues at the carboxy-terminus of the pilin protein. One of these mutants had a pleiotropic affect on pilus function and was thought to have affected pilus assembly. The sixthe point mutant (WPFL51), previously thought to be in traA, was complemented by chimeric plasmids carrying the traG gene of the F transfer region, which may be involved in the acetylation of the pilin subunit. A traA nonsense mutant (JCFL1) carried an amber mutation near the amino-terminus which is well suppressed in SuI⁺ (supD) and SuIII⁺ (supF) strains. Neither the antigenicity of the pilin nor the efficiency of plating of F-specific bacteriophages were affected when this plasmid was harbored by either suppressor strain. A second amber mutant (JCFL25) which is not suppressible, carried its mutation in the codon for the single tryptophan in F pilin, suggesting that this residue is important in subunit interactions during pilus assembly. Two other point mutants (JCFL32 and 44) carried missense mutations in the leader sequence (positions 9 and 13) which affected the number of pili per cell presumably by altering the processing of propilin to pilin.     

Cloning of hemA from Rhizobium sp. NGR234 and symbiotic phenotype of a gene-directed mutant in diverse legume genera

Summary The hemA gene which encodes -aminolaevulinic acid synthase (ALAS), was cloned and characterized from the broad host-range Rhizobium strain NGR234. A cosmid, identified by hybridization with the cloned gene of R. meliloti and complementation of an R. meliloti hemA mutant, was subcloned to yield a 5.5 kb fragment containing the entire NGR234 gene. A physical-genetic map was made and the interposon was introduced into a single EcoRI site which bisects the gene. The mutated gene was homogenotized into NGR234 to generate a hemA mutant, with a view to evaluating the role of rhizobial bacteroid ALAS activity for a wide variety of legume symbioses. The mutant strain formed an ineffective (Fix^–) symbiosis with all tested host plants. These included tropical legumes that produce either indeterminate (Leucaena) or determinate (Desmodium, Macroptilium, Lablab, Vigna) root nodules.Abbreviations ALA -aminolaevulinic acid - ALAS aminolaevulinic acid synthase - Lb leghaemoglobin - Lb-haem haem moiety of leghaemoglobin     

The marginal regions of thylakoid membranes: A partial characterization by polyoxyethylene sorbitan monolaurate (Tween 20) solubilization of spinach thylakoids

The detergent Tween-20 solubilized preferentially portions of the marginal regions of Spinacea oleracea L. thylakoid membranes and, thus, opened the inside of the grana to the external media. Differential centrifugation. following Tween-20 solubilization. enabled separate fractions of grana and stromal-exposed membranes to be isolated. Analysis of Tween-20 solubilized material, after pelleting all membrane material by centrifugation at 100 000 g, revealed polypeptides associated with the coupling factor (CF₁) particles, cytochrome b₆/f and photosystem II complexes, suggesting that the marginal membranes contain these proteins. Concomitantly, the 100 000 g pellet was depleted in cytochrome b₆/f and P700, determined spectroscopically, Thus. our results reveal the margin to be a distinct membrane region, which does not contain the light-harvesting centers of photosystem II (LHC II). The implication of these results, in terms of the energetic interaction of components of granal and stromalexposed membrane regions, is discussed.     

Measurement of light within thin plant tissues with fiber optic microprobes

Vogelmann, T. C., Knapp, A. K., McClean, T. M. and Smith, W. K. 1988. Measurement of light within thin plant tissues with fiber optic microprobes. - Physiol. Plant. 72: 623–630.
The measurement of light with fiber optic microprobes has been extended to thin (200–300 μm) plant tissue samples. To test the method, light measurements were made in thin aqueous films and paradermal sections from 10-day-old etiolated Cucurbita pepo L. cv. Fordhook cotyledons. The measurements obtained were highly reproducible. Paradermal sections of spongy mesophyll that were irradiated with collimated light scattered light more effectively than the palisade layer of intact cotyledons. These results demonstrate that different plant tissues have different light scattering characteristics. The successful extension of the fiber optic microprobe technique to thin systems makes it possible to examine the optical properties of different cell layers within leaves and other plant organs.     

Comparison of the seed germination effects of synthetic analogs of strigol,gibberellic acid,cytokinins, and other plant growth regulators

Four synthetic multiring analogs of strigol, a naturally occurring sesquiterpene lactone that promotes germination of dormant seeds ofStriga (witchweed), were found to stimulate germination of dormantLactuca (lettuce) seeds. The effects on light-sensitive and light-insensitive lettuce seeds were concentration-dependent and exceeded those produced by equimolar (0.1 mM) solutions of gibberellic acid. Strigol and epistrigol promoted lettuce seed germination to a lesser degree than did the synthetic analogs. The strigol group compounds had minimal effect on the germination of monocot seeds. The results indicate that the synthetic strigol analogs have plant growth regulatory activity in dormant seeds of genera beyondStriga in which germination stimulation by strigol and the synthetic analogs was first demonstrated.Names of companies of commercial products are given solely for the purpose of providing specific information; their mention does not imply recommendation or endorsement by the U.S. Department of Agriculture over others not mentioned.     

Blood glucose discrimination training in insulin-dependent diabetes mellitus (IDDM) patients

Self-management of insulin-dependent diabetes mellitus (IDDM) is dependent on a negative feedback loop of blood glucose (BG) fluctuations, which in turn directs treatment decisions to maintain normal BG. Although this feedback is typically accomplished by self-monitoring of blood glucose (SMBG), SMBG has limitations, and patients often rely on what their BG feels like. Two studies were performed to evaluate whether patients could learn to more accurately feel/discriminate their BG on the basis of internal cues or internal plus external BG cues. In Study I, BG Awareness Training significantly improved pre- to posttreatment BG estimation accuracy, relative to a control group. Study II replicated BG Awareness Training efficacy in improving BG estimation accuracy. Improvement in estimation accuracy was related only to initial accuracy; those who were initially less accurate improved the most. This improvement was represented in a 31% reduction in dangerous BG estimation errors and a 9% increase in accurate estimates. Resulting estimations were, however, still significantly less accurate than SMBG at the end of training.This research was supported by NIH grants AM282880, AM24177, AM22125, and RR00847 and by the Ames Company. The authors express their appreciation for the contribution made by trainers Leslie Butterfield and Linda Zimbelman, by the nursing staff at the University of Virginia's Clinical Research Center and the Diabetes and Nutrition Unit, and by Dr. James May from the Medical College of Virginia in soliciting subjects. We would also like to thank Andrea Snyder for her assistance.     

Daily relaxation modifies serum and salivary immunoglobulins and psychophysiologic symptom severity

This study investigated the effect of daily relaxation on concentrations of serum immunoglobulins A, G, and M and secretion rates of salivary immunoglobulin A (S-IgA). Twenty-four volunteers were randomly assigned to practice a relaxation technique daily for 3 weeks and 16 to a waiting list control condition. Blood and saliva samples were collected before and after a supervised 20-min relaxation session at the beginning and end of the 3-week practice period. S-IgA secretion rate increased significantly (p<.001) after 20 min of relaxation. A longer-term practice effect also occurred in that the increase in secretion rate in before to after relaxation samples was higher (p=.014) in subjects who had practiced relaxation once a day for 3 weeks than in waiting list control subjects practicing for the first time. Serum IgA (p<.001), IgG (p<.001), and igM (p<.05) increased significantly over the 3-week practice period. Relaxation may be a self-regulating strategy affecting both humoral and cellular divisions of the immune system.Parts of this paper were presented at the annual meeting of the Biofeedback Society of America, March 1987. Materials for the IgA assays were provided by Cooper Biomedical, Malvern, Pennsylvania.