Differential effects of amino acid substitutions in the beta-sheet floor and alpha-2 helix of HLA-A2 on recognition by alloreactive viral peptide-specific cytotoxic T lymphocytes

Crystallographic studies of the HLA-A2 molecule have led to the assignment of a putative peptide binding site that consists of a groove with a beta-pleated sheet floor bordered by two alpha-helices. A CTL-defined variant of HLA-A2, termed HLA-A2.2F, differs from the common A2.1 molecule by three amino acids: a Leu to Trp substitution at position 156 in the alpha-2 helix, a Val to Leu substitution at position 95 in the beta-sheet floor of the groove, and a Gln to Arg substitution at position 43 in a loop outside of the groove. Another HLA-A2 variant, termed CLA, has a single Phe to Tyr substitution at position 9 that is sterically located adjacent to position 95 in the beta-sheet floor of the groove. We have determined which of the amino acid substitutions at positions 9, 43, 95, or 156 could individually affect recognition by panels of A2.1 allospecific and A2.1-restricted influenza viral matrix peptide-specific CTL lines, using a panel of site-directed mutants and CLA. Recognition by allospecific CTL lines was generally unaffected by any one of the amino acid substitutions, but was eliminated by the double substitution at positions 95 and 156. Allorecognition by some CTL lines was eliminated by a single substitution at position 9 or 95. In contrast, recognition by A2.1-restricted matrix peptide specific CTL was totally eliminated by a single substitution at position 9 or 156. The substitution at position 43 in a loop away from the peptide binding groove had no effect on allorecognition or matrix peptide recognition. These results indicate that amino acid residues in the floor or alpha-2 helical wall of the peptide binding groove of the HLA-A2 molecule can differentially affect allorecognition and viral peptide recognition.     

A small acidic protein 1 (SMAP1) mediates responses of the Arabidopsis root to the synthetic auxin 2,4-dichlorophenoxyacetic acid

2,4-dichlorophenoxyacetic acid (2,4-D), a chemical analogue of indole-3-acetic acid (IAA), is widely used as a growth regulator and exogenous source of auxin. Because 2,4-D evokes physiological and molecular responses similar to those evoked by IAA, it is believed that they share a common response pathway. Here, we show that a mutant, antiauxin resistant1 (aar1), identified in a screen for resistance to the anti-auxin p-chlorophenoxy-isobutyric acid (PCIB), is resistant to 2,4-D, yet nevertheless responds like the wild-type to IAA and 1-napthaleneacetic acid in root elongation and lateral root induction assays. That the aar1 mutation alters 2,4-D responsiveness specifically was confirmed by analysis of GUS expression in the DR5:GUS and HS:AXR3NT-GUS backgrounds, as well as by real-time PCR quantification of IAA11 expression. The two characterized aar1 alleles both harbor multi-gene deletions; however, 2,4-D responsiveness was restored by transformation with one of the genes missing in both alleles, and the 2,4-D-resistant phenotype was reproduced by decreasing the expression of the same gene in the wild-type using an RNAi construct. The gene encodes a small, acidic protein (SMAP1) with unknown function and present in plants, animals and invertebrates but not in fungi or prokaryotes. Taken together, these results suggest that SMAP1 is a regulatory component that mediates responses to 2,4-D, and that responses to 2,4-D and IAA are partially distinct.     

Effect of temperature, light and salinity on seed germination and radicle growth of the geographically widespread halophyte shrub Halocnemum strobilaceum

BACKGROUND AND AIMS: The small leafy succulent shrub Halocnemum strobilaceum occurs in saline habitats from northern Africa and Mediterranean Europe to western Asia, and it is a dominant species in salt deserts such as those of north-west China. The effects of temperature, light/darkness and NaCl salinity were tested on seed germination, and the effects of salinity were tested on seed germination recovery, radicle growth and radicle elongation recovery, using seeds from north-west China; the results were compared with those previously reported on this species from 'salt steppes' in the Mediterranean region of Spain. METHODS: Seed germination was tested over a range of temperatures in light and in darkness and over a range of salinities at 25 degrees C in the light. Seeds that did not germinate in the NaCl solutions were tested for germination in deionized water. Seeds from which radicles had barely emerged in deionized water were transferred to NaCl solutions for 10 d and then back to deionized water for 10 d to test for radicle growth and recovery. KEY RESULTS: Seeds germinated to higher percentages in light than in darkness and at high than at low temperatures. Germination percentages decreased with an increase in salinity from 0.1 to 0.75 M NaCl. Seeds that did not germinate in NaCl solutions did so after transfer to deionized water. Radicle elongation was increased by low salinity, and then it decreased with an increase in salinity, being completely inhibited by > or = 2.0 M NaCl. Elongation of radicles from salt solutions < 3.0 M resumed after seedlings were transferred to deionized water. CONCLUSIONS: The seed and early seedling growth stages of the life cycle of H. strobilaceum are very salt tolerant, and their physiological responses differ somewhat between the Mediterranean 'salt steppe' of Spain and the inland cold salt desert of north-west China.     

Ecology of two geographically restricted Astragalus species (Fabaceae), A. bibullatus and A. tennesseensis, of the eastern United States

Astragalus bibullatus is endemic to limestone glades in the Central Basin of Tennessee, and except for one population in Illinois,A. tennesseensis is endemic to limestone glades in the Central Basin and in the Moulton Valley of Alabama. However,A. tennesseensis has been extirpated from four counties in Illinois, from its only known site in Indiana, from one county in Tennessee, and from one county in Alabama.Astragalus bibullatus is closely related to the geographically wide-spread Great Plains taxonA. crassicarpus var.crassicarpus (sectionSarcocarpi), whereasA tennesseensis is the only taxon in sectionTennesseensis. Both species are shallow-rooted, hemicryptophyte perennials without vegetative reproduction, have no effective means of seed dispersal, form long-lived seed banks, have similar life cycle phenologies, are intolerant of heavy shade, and have moderate amounts of genetic diversity. Much. additional information is available on the autecology ofA. tennesseensis. Its primary habitat is the transition zone between open glades and glade woods, where physical environmental factors are intermediate between those of the adjacent zones. Seedling-juvenile survival is low. Plants flower first in their second to fifth year and only a few times before dying, are self-incompatible, respond to drought by shedding leaves and by accumulating large amounts of proline, and compete poorly. Populations exhibit high fluctuations in number of individuals and have high turnover rates. A greenhouse study ofA bibullatus andA crassicarpus var.crassicarpus did not identify any difference in responses of these species to light or soil moisture that could account for the great differences in geographic ranges. Thus, historical factors were also considered to explain the narrow endemism ofA. bibullatus. Finally, we present previously unpublished data on the effect of light level and of competition with the cedar glade dominantSporobolus vaginiflorus in several watering regimes on growth ofA. tennesseensis. The role of these factors in restriction of this species to its transition zone microhabitat is discussed.     

IL-1 beta modulation of spontaneous autoimmune diabetes and thyroiditis in the BB rat

Long term effects of in vivo treatment with human rIL-1 beta on diabetogenesis and thyroid disease were determined in the Biobreeding rat. Administration of high dose (10 micrograms/kg) IL-1 beta accelerated the onset of insulin-dependent diabetes mellitus compared to saline-injected controls. High dose treatment resulted in goiter development, pronounced LT, reduced serum T4 levels, and overall growth reduction. In contrast, low dose IL-1 beta (0.5 microgram/kg) administration significantly reduced the frequency of insulin-dependent diabetes mellitus (48%) compared to placebo (86%) and high dose IL-1 beta (93%) treatment groups. Rats protected by low dose IL-1 beta had unaffected growth rates and minimal to no pancreatic and thyroid pathology. Our results demonstrate that exogenous administration of IL-1 beta modulates Biobreeding rat idiopathic autoimmune diabetes and thyroid disease in a dose-dependent manner.     

Rigorous analysis of light diffraction by a striated muscle fibre.

A rigorous theory describing the diffraction of light by a muscle fibre has been formulated. The basis of this analysis is the rigorous coupled-wave approach of T. K. Gaylord & M. G. Moharam (Proc. IEEE 73, 894 (1985)); however, we obtain here a closed-form analytical result that is both mathematically simple and physically easy to understand. We have compared our results on striated muscle fibres with the analytical results obtained by A. F. Huxley (Proc. R. Soc. Lond. B 241, 65 (1990)) using the normal mode approach, and with those obtained by R. A. Thornhill, N. Thomas & N. Berovic (Eur. Biophys. J. 20, 87 (1991)) using a multiwave first-order coupled-wave approximation. For an equivalent set of assigned fibre parameters, our results are consistent with these mentioned. Extension of this analysis to a fibre with different structures showed that the differences in diffraction efficiencies of different orders for a frog skeletal fibre and for an insect flight fibre are clear; the sensitivity to distinct structural organization of the fibre is very good.     

Does dormancy protect seeds against attack by the pathogenic fungus <Emphasis Type="Italic">Fusarium tricinctum</Emphasis> in a semiarid grassland of Northwest China?

Aims

Soil fungal pathogens can result in the failure of seedling establishment, but the effects of fungicide applications on seed/seedling survival have differed among studies. We assumed that the variation may relate to seed dormancy/germination characteristics and hypothesized that nondormant germinating seeds are more likely to be killed by fungal pathogens than dormant seeds.

Methods

Dormant and nondormant seeds of Stipa bungeana and Lespedeza davurica were inoculated with a pathogenic fungus Fusarium tricinctum under laboratory and field conditions. The outcomes of seed/seedling fate and other parameters were evaluated.

Results

In the laboratory, nondormant seeds inoculated with F. tricinctum developed white tufts of mycelium on the radicles of germinating seeds causing them to quickly die, but dormant seeds remained intact. In contrast, in the field inoculation with F. tricinctum did not cause higher mortality of nondormant than dormant seeds but resulted in higher percentages of seedling death before they emerged from soil than the controls.

Conclusions

Our results suggest that dormancy protects seeds from being attacked by some pathogens by preventing germination, but the protection is lost once germination has commenced. Further study involving various plant species with more seeds is needed to assess the generality of this pathogen-seed interaction hypothesis.

     

The inactivation of rhodanese by nitrite and inhibition by other anions in vitro

Cyanide detoxification in mammals occurs, in part, by sulfur transfer by rhodanese to form the less toxic thiocyanate. Thiosulfate and nitrite are often used in combination for the treatment of cyanide intoxication. This report shows that nitrite can inhibit the rate of sulfur transfer by rhodanese in vitro. Nitrate, chloride, sulfate, and acetate were also examined as inhibitors. Inhibition by nitrite appeared to be more complex than for the other anions tested. Closer examination showed that nitrite can inactivate the sulfur-free rhodanese. Our observation leads to the suggestion that, in vivo, either rhodanese is maintained in its more stable sulfur-substituted form or cellular compartmentalization prevents inactivation by nitrite.     

Evaluation of the anthracene-benzene chemical light meter for ecological research

Summary The anthracene-benzene chemical light meter is used in ecological studies to measure solar radiation. The meter absorbs only in the ultraviolet (UV) and, in principle, relies on the conversion, by solar UV, of anthracene to dianthracene. In practice, the investigator uses a calibration curve to convert decrease of anthracene in solution to solar radiation received. Our results show that significant errors occur when a calibration curve is used under different atmospheric conditions than those under which it is prepared. The reason is that the ratio of solar UV to other portions of the solar spectrum reaching the earth's surface is modified by atmospheric conditions. Furthermore, percentage of UV in the solar spectrum is modified by latitude, season, time of day, atmospheric pollutants and layers of water and vegetation. Thus, successful use of light meters that utilize chemical conversions by solar UV to measure other portions of the solar spectrum are dependent on the preparation of a calibration curve for each condition under which the meter is used.