Chromosome mapping of low-temperature induced Wcs120 family genes and regulation of cold-tolerance expression in wheat

 Low-temperature (LT) induced genes of the Wcs120 family in wheat (Triticum aestivum) were mapped to specific chromosome arms using Western and Southern blot analysis on the ditelocentric series in the cultivar Chinese Spring (CS). Identified genes were located on the long arms of the homoeologous group 6 chromosomes of all 3 genomes (A, B, and D) of hexaploid wheat. Related species carrying either the A, D, or AB genomes were also examined using Southern and Western analysis with the Wcs120 probe and the WCS120 antibody. All closely related species carrying one or more of the genomes of hexaploid wheat produced a 50 kDa protein that was identified by the antibody, and a Wcs120 homoeologue was detected by Southern analysis in all species. In the absence of chromosome arm 6DL in hexaploid CS wheat no 50 kDa protein was produced and the high-intensity Wcs120 band was missing, indicating 6DL as the location of Wcs120 but suggesting silencing of the Wcs120 homoeologue in the A genome. Levels of proteins that cross-reacted with the Wcs120 antibody and degrees of cold tolerance were also investigated in the Chinese Spring/Cheyenne (CS/CNN) chromosome substitution series. CNN chromosome 5A increased the cold tolerance of CS wheat. Densitometry scanning of Western blots to determine protein levels showed that the group 5 chromosome 5A had a regulatory effect on the expression of the Wcs120 gene family located on the group 6 chromosomes of all three hexaploid wheat genomes. Received: 10 July 1996 / Accepted: 30 September 1996     

Genetic analysis of sterile mutants in the dpy-5 unc-13 (I) genomic region of Caenorhabditis elegans

Essential genes were identified in the 1.5-map unit dpy-5 unc-13 region of chromosome I in the Caenorhabditis elegans genome by rescuing lethal mutations using the duplication sDp2. In this paper, we report the mapping and complementation testing of lethal mutations, 45 of which identify 18 new, essential genes. This analysis brings the number of essential genes defined by the sDp2 rescue of lethal mutants to 97; 64 of these map between dpy-5 and unc-13. 61% of these essential genes are identified by more than one allele. Positioning of the mutations was done using the breakpoints of six duplications. The mutant phenotypes of 14 loci essential for fertility were characterized by Nomarski microscopy and DAPI staining. None of the mutants were rescued by wild-type male sperm. The cytological data showed that four genes produced mutants with defects in gonadogenesis, let-395, let-603, let-605 and let-610. Mutations in seven genes, let-355, let-367, let-384, let-513, let-544, let-545 and let-606, affected germ cell proliferation or gametogenesis. Mutants for the remaining three genes, let-370, let-599 and let-604, produced eggs that failed to develop or hatch, thereby acting as maternal effect lethals. We observed a nonrandom distribution of arrest phenotypes with regard to map position. Received: 8 May 1996 / Accepted : 27 January 1997     

Highly independent olfactory receptor sites for naturally occurring bile acids in the sea lamprey, Petromyzon marinus

(1) Electro-olfactogram recording was used to determine whether the olfactory epithelium of adult sea lamprey is specifically sensitive to bile acids, some of which have been hypothesized to function as pheromones. Ten bile acids were selected from 38 which had already been pre-screened for olfactory activity. These compounds were first tested on their own, then as adapting stimuli, and finally as components of mixtures (2) The lamprey-specific bile acids, petromyzonol sulfate and allocholic acid, were the most potent compounds tested. Five other bile acids were also detectable at picomolar concentrations. Petromyzonol sulfate had a distinctive dose-response curve. (3) Cross-adaptation demonstrated that sensitivity to bile acids is attributable to at least four independent classes of olfactory receptor sites and that both the nature and position of conjugating group(s) are critical to receptor specificity. Notably, petromyzonol sulfate has its own highly specific and independent receptor site. The situation for unconjugated bile acids was more complex and there appeared to be several sub-classes of receptor sites for these compounds. (4) Mixture studies largely confirmed the cross-adaptation results, describing receptor site independence for the same four sets of odorants. Mixture enhancement was also seen when expected and there was no evidence of mixture suppression. (5) Together, these data demonstrate that conspecific bile acids are discriminated by the olfactory epithelium of the sea lamprey, supporting the possibility that these compounds may function as migratory pheromones. Accepted: 23 November 1996     

Cloning and genetic mapping of wheat telomere-associated sequences

Wheat telomere-associated sequences (TASs) were cloned using a Vectorette approach and sequenced. Reverse primers specific to the TASs were combined with labelled degenerate telomere primers in PCR reactions containing total genomic DNA as template. Amplification products were separated on sequencing gels. In total, seventeen primer combinations provided 47 polymorphic fragments. Nine of these mapped beyond the most distal RFLP markers and defined the ends of seven chromosome arms. Seven of the nine terminal fragments were derived from a 118-bp tandem repeat, indicating that subtelomeric tandem repeat sequences provide an efficient means to target chromosome ends. A telomere cloning strategy and the terminal and interstitial location of TASs are discussed. Received: 13 September 1996 / Accepted: 22 January 1997     

Patch clamp study and kinetic modeling on the most abundant chloride channel on distal fibers of crayfish opener muscle

Whereas the inhibitory innervation of the deep extensor abdominal muscle in crayfish is mediated by a weakly acting common inhibitor, the opener muscle exhibits a stronger inhibition. In the present study the most abundant γ-aminobutyric acid-activated chloride channel on distal fibers of crayfish opener muscle was characterized by measuring the current responses after applying pulses of γ-aminobutyric acid to outside-out patches. The results were compared to those obtained earlier with the chloride channel on the deep extensor abdominal muscle of the same species. The double logarithmic plot of the dose-response relationship had a slope of n _H = 2.2 in contrast to n _H = 5.3 for the channel on the deep extensor abdominal muscle. The rise time of the current response declined to 1 ms at a γ-aminobutyric acid concentration of 50 mmol · l⁻¹. With lower concentrations the rise time increased to a maximal value of 280 ms. No peak of the rise time at low γ-aminobutyric acid concentrations, as observed for the channel on the deep extensor abdominal muscle, was obvious. The open and closed times were similar to those of the channel of the deep extensor abdominal muscle. Different reaction schemes were discussed to describe the kinetics of the chloride channel of the opener muscle. Accepted: 12 August 1996     

Effects of plant hybridization on herbivore-parasitoid interactions

We studied the effects of host plant hybridization on the survival and mortality of the leaf-mining moth Phyllonorycter salicifoliella on hybrid and parental willow plants in the field and in a common garden experiment. P. salicifoliella survival differed significantly among three willow taxa in the field in 1994 but not in the field in 1995 or in the common garden. Parasitism by eulophid wasps differed significantly among taxa in 1994 and appeared to account for the variation in their survival. In the field in 1995, host feeding predation varied significant among taxa. The theory of tritrophic interactions predicts that plant genotype can affect natural enemy impact, and this study supports this prediction. Significant variation in survival and eulophid parasitism was also found among genotypes within taxa in the field in both years and in the common garden experiment. The common garden results show that genetic differences in plants affect the herbivore-parasitoid interaction. Variation among years in the patterns of survival and causes of mortality among field plants suggest that genotype by environment interactions may be important. Received: 1 March 1996 / Accepted: 4 November 1996     

Shade-induced changes in the branching pattern of a stoloniferous herb: functional response or allometric effect?

Shade-induced changes in the branching pattern of clonal plants can lead to conspicuous modifications of their growth form and architecture. It has been hypothesized that reduced branching in shade may be an adaptive trait, enabling clonal plants to escape from unfavourable patches in a heterogeneous environment by allocating resources preferentially to the growth of the main axis (i.e. linear expansion), rather than to local proliferation by branching. However, such an adaptionist interpretation may be unjustified if (1) branching frequency is a function of the ontogenetic stage of plants, and if (2) shading slows down the ontogenetic development of plants, thereby delaying branch formation. In this case, architectural differences between sun- and shade-grown individuals, harvested at the same chronological age, may not represent a functional response to changes in light conditions, but may be a by-product of effects of shade on the rate of plant development. To distinguish between these two alternatives, individuals of the stoloniferous herb Potentilla reptans were subjected to three experimental light conditions: a control treatment providing full daylight, and two shade treatments: neutral shade (13% of ambient PPFD; no changes in light spectral composition) and simulated canopy shade (13% PPFD and a reduced red:far-red ratio). Plant development was followed throughout the experiment by daily monitoring primary stolon growth as well as branch and leaf initiation. Biomass and clonal offspring production were measured when plants were harvested. At the end of the experiment shaded plants had produced significantly fewer branches than clones grown in full daylight. In all three treatments, however, initiation of secondary stolons occurred at the same developmental stage of individual ramets. Shading significantly slowed down the ontogenetic development of plants and this resulted in the observed differences in branching patterns between sun- and shade-grown individuals, when compared at the same chronological age. These results hence provide evidence that shade-induced changes in the branching pattern of clonal plants can be due to purely allometric effects. Implications for interpreting architectural changes in terms of functional shade-avoidance responses are discussed. Received: 16 August 1996 / Accepted: December 1996