AN OVERVIEW OF THE GENUS PYRRHOPAPPUS (ASTERACEAE: LACTUCEAE) WITH EMPHASIS ON CHLOROPLAST DNA RESTRICTION SITE DATA

The genus Pyrrhopappus in recent systematic treatments has comprised five taxa (four species, one with two varieties), which have now been studied anew using morphogeographical and chloroplast DNA restriction site data. Eight populations, representing all of the recognized taxa of Pyrrhopappus, were digested with 17 restriction enzymes. Only three restriction site differences were found from among 750 restriction sites and no length variations were observed. This contrasts with similar studies, using these same enzymes, on the closely related genus Krigia in which 173 mutation sites and 20 length variations were found among the seven species concerned. Nucleotide sequence divergence values among the species of Pyrrhopappus were extremely low (0.0012) compared to much higher values found in the closely related genus Krigia (0.1270). Three species of Pyrrhopappus are herein recognized: two diploids with 2n = 12 chromosomes, P. carolinianus and P. pauciflorus (including P. multicaulis, P. geiseri and P. rothrockii), and a tetraploid (2n = 24), P. grandiflorus. The tetraploid is partially sympatric with both diploids but is readily recognized by its perennial roots, which bear tuber-like enlargements. These three species presumably arose relatively recently, and the DNA data suggest that neither P. pauciflorus nor P. carolinianus gave rise to the tetraploid P. grandiflorus.     

Influence of clay minerals on sorption of bacteriolytic enzymes

Myxobacteria presumably produce extracellular bacteriolytic enzymes when they are growing in soil. In order to study their ecological significance, adsorption experiments were performed with lytic enzymes produced byMyxococcus virescens in casitone media. Different soils as well as montmorillonite and kaolinite can rapidly adsorb the bacteriolytic but not the proteolytic enzymes. About 1 gm of montmorillonite per liter of cell-free culture solution is enough for the adsorption of 97% of the bacteriolytic enzymes. The adsorption per unit weight is about 100 times greater on montmorillonite than on kaolinite. About 40% of the adsorbed enzymes can be eluted with solutions of high pH or high ionic strength. The only desorbed bacteriolytic enzyme is the alanyl-∈-N-lysine endopeptidase.     

AvrRps4 effector family processing and recognition in lettuce

During pathogenesis, effector proteins are secreted from the pathogen to the host plant to provide virulence activity for invasion of the host. However, once the host plant recognizes one of the delivered effectors, effector‐triggered immunity activates a robust immune and hypersensitive response (HR). In planta, the effector AvrRps4 is processed into the N‐terminus (AvrRps4^N) and the C‐terminus (AvrRps4^C). AvrRps4^C is sufficient to trigger HR in turnip and activate AtRRS1/AtRPS4‐mediated immunity in Arabidopsis; on the other hand, AvrRps4^N induces HR in lettuce. Furthermore, AvrRps4^N‐mediated HR requires a conserved arginine at position 112 (R112), which is also important for full‐length AvrRps4 (AvrRps4^F) processing. Here, we show that effector processing and effector recognition in lettuce are uncoupled for the AvrRps4 family. In addition, we compared effector recognition by lettuce of AvrRps4 and its homologues, HopK1 and XopO. Interestingly, unlike for AvrRps4 and HopK1, mutation of the conserved R111 in XopO by itself was insufficient to abolish recognition. The combination of amino acid substitutions arginine 111 to leucine with glutamate 114 to lysine abolished the XopO‐mediated HR, suggesting that AvrRps4 family members have distinct structural requirements for perception by lettuce. Together, our results provide an insight into the processing and recognition of AvrRps4 and its homologues.     

Staining of Some Specific Regions of Human Chromosomes,particularly the Secondary Constriction of No. 9

SEVERAL procedures have been described recently which produce specific patterns of differential staining in human chromosomes^1–9. Techniques which involve DNA denaturation and reannealing reveal deeply stained areas on centromere and secondary constriction regions which have been equated with constitutive heterochromatin⁹.     

The mode of action of thidiazuron: auxins,indoleamines, and ion channels in the regeneration of <Emphasis Type="Italic">Echinacea purpurea</Emphasis> L.

The biochemical mechanisms underlying thidiazuron (TDZ)-induced regeneration in plant cells have not been clearly elucidated. Exposure of leaf explants of Echinacea purpurea to a medium containing TDZ results in undifferentiated cell proliferation and differentiated growth as mixed shoot organogenesis and somatic embryogenesis. The current studies were undertaken to determine the potential roles of auxin, indoleamines, and ion signaling in the dedifferentiation and redifferentiation of plant cells. E. purpurea leaf explants were found to contain auxin and the related indoleamine neurotransmitters, melatonin, and serotonin. The levels of these endogenous indoleamines were increased by exposure to TDZ associated with the induction of regeneration. The auxin-transport inhibitor 2,3,5-triiodobenzoic acid and auxin action inhibitor, p-chlorophenoxyisobutyric acid decreased the TDZ-induced regeneration but increased concentrations of endogenous serotonin and melatonin. As well, inhibitors of calcium and sodium transport significantly reduced TDZ-induced morphogenesis while increasing endogenous indoleamine content. These data indicate that TDZ-induced regeneration is the manifestation of a metabolic cascade that includes an initial signaling event, accumulation, and transport of endogenous plant signals such as auxin and melatonin, a system of secondary messengers, and a concurrent stress response.     

Kinetic Monte Carlo simulation for the striation distribution of void defects in Czochralski silicon growth

Unique crystal-originated pit (COP) distribution, similar to a striation pattern, is well matched with the oxygen profile in experimental analysis. It shows the strong relationship between oxygen concentration and COP distribution. In this paper, we study the generation of void defects and the relationship between interstitial oxygen and vacancy using the kinetic lattice Monte Carlo (KLMC) method. The KLMC method has been applied extensively in various forms to the study of micro-defects in silicon wafers. It explained well the formation of void defects such as vacancy–oxygen complex and vacancy–vacancy complex. The formation of clusters is strongly affected by oxygen concentration, which showed the relationship between COP distribution and oxygen concentration. The unique COP distribution could be correctly explained with KLMC results, and this kind of meso-scale results has not yet been reported.