No abstract

Pollen is an important vector of gene flow in maize (Zea mays L.). Experiments were conducted to investigate the duration of pollen viability and the effectiveness of isolation distance for controlling gene flow. Pollen longevity was tested by collecting pollen at dehiscence and exposing it in a thin layer in the open air and sunshine for prescribed time periods before assessing pollen viability by measuring seed set after pollination and scoring visual appearance. Isolation distance efficacy was evaluated by growing 12.8‐m2 plot of maize at various distances from a 4000‐m2 pollen source. The pollinator contained either a genetic leaf or seed marker that allowed pollen flow to be measured. Pollen maintained viability for 1 to 2 h after dehiscence depending on atmospheric water potential. The theoretical, maximum distance viable pollen could move was 32 km, assuming pollen was transported linearly at the maximum average afternoon windspeeds for our location, viability was maintained for 2 h, and pollen settling rate was ignored. Cross pollinations occurred at a maximum distance of 200 m from the source planting, and only a limited number of cross pollinations occurred at the shortest distance (100 m). No cross pollinations occurred at 300 m from the source planting. The results are consistent with conclusions that maize pollen is desiccation intolerant and has a high settling rate. The results indicate isolation distance can be a useful tool for controlling gene flow via pollination in research scale plantings.

Helicobacter pylori is involved in gastritis, gastric and duodenal ulcers, gastric adenocarcinoma, and mucosaassociated lymphoid tissue lymphoma. Earlier studies already suggested a role for autoimmune phenomena in H. pylori-linked disease. We now report that lipopolysaccharides (LPS) of H. pylori express Lewis y, Lewis x, and H type I blood group structures similar to those commonly occurring in gastric mucosa. Immunization of mice and rabbits with H. pylori cells or purified LPS induced an anti-Lewis x or y or anti-H type I response, yielding antibodies that bound human and murine gastric glandular tissue, granulocytes, adenocarcinoma, and mucosa-associated lymphoid tissue lymphoma cells. Experimental oral infections in mice or natural infection in humans yielded anti-Lewis antibodies also. The ␤ chain of gastric H ؉ ,K ؉ -ATPase, the parietal cell proton pump involved in acid secretion, contained Lewis y epitopes; gastric mucin contained Lewis x and y antigenic determinants. Growth in mice of a hybridoma that secretes H. pylori-induced anti-Lewis y monoclonal antibodies resulted in histopathological evidence of gastritis, which indicates a direct pathogenic role for anti-Lewis antibodies. In conclusion, our observations demonstrate that molecular mimicry between H. pylori LPS and the host, based on Lewis antigens, and provide understanding of an autoimmune mechanism for H. pylori-associated type B gastritis.

In addition to the major encapsidated DNA species found in preparations of cassava latent virus (genomic DNAs 1 and 2) there are minor DNA populations of twice (dimeric) and approximately half genome length. Both minor species resemble the genomic DNAs in that they are composed of predominantly circular single-stranded DNA. All of these size groups have a corresponding covalently-closed circular double-stranded DNA form in infected tissue. Infectivity studies using cloned DNAs 1 and 2 show that dimeric DNA routinely appears, suggesting it to be an intermediate in the DNA replicative cycle that can be encapsidated at low efficiency. In contrast, half unit length DNA has not yet been detected after multiple passaging of virus derived from the cloned DNA inoculum. Half unit length DNAs appear to be derived exclusively from DNA 2 and consist of a population of molecules exhibiting a relatively specific deletion. As they have an inhibitory effect on virus multiplication, their encapsidated forms are analogous to defective interfering particles associated with other eukaryotic DNA containing viruses. Small primer molecules associated with the genomic single-stranded DNAs, as reported for another geminivirus, have not been detected in CLV.

The nucleotide sequences of infectious cloned DNAs 1 and 2 of a Kenyan isolate of cassava latent virus (CLV) have been determined. Five virus‐specific polyadenylated transcripts have been identified and mapped either to the viral or complementary sense DNAs of both components of the CLV genome, confirming that transcription is bidirectional on both DNAs. A major mRNA has been translated in vitro to yield a 30 000 mol. wt. product, which is precipitated by antibodies raised against whole virus, and has been mapped by both the S1 nuclease procedure and hybrid‐arrested translation to the long open reading frame (ORF) in the viral sense of DNA 1 which encodes the coat protein. Other transcripts were of sufficient size and appropriate origin to encode at least five potential products.

Intact recombinant DNAs containing single copies of either component of the cassava latent virus genome can elicit infection when mechanically inoculated to host plants in the presence of the appropriate second component. Characterisation of infectious mutant progeny viruses, by analysis of virus-specific supercoiled DNA intermediates, indicates that most if not all of the cloning vector has been deleted, achieved at least in some cases by intermolecular recombination in vivo between DNAs 1 and 2. Significant rearrangements within the intergenic region of DNA 2, predominantly external to the common region, can be tolerated without loss of infectivity suggesting a somewhat passive role in virus multiplication for the sequences in question. Although packaging constraints might impose limits on the amount of DNA within geminate particles, isolation of an infectious coat protein mutant defective in virion production suggests that packaging is not essential for systemic spread of the viral DNA.

A non-helical strain of Spiroplasma citri from little-leaf diseased oranges was subcultured over 40 times in different media without producing helical cells. It was non-motile and produced colonies of a characteristic morphology on soft agar plates. Serology, DNA hybridization and toxin production confirmed that it was a strain of S. citri but its membrane protein pattern after polyacrylamide gel electrophoresis differed from those of other S. citri strains in that one band was absent. The organism caused symptoms in plants identical to those produced by a pathogenic helical strain of S . citri. I N T R O D U C T I O NSpiroplasmas differ from other Mollicutes in shape and motility. All those isolated are typically helical during at least part of their growth phase and show rotary or 'screw'-like motility as well as flexing movements. The helical shape is apparently maintained without the assistance of a rigid cell wall or axial filaments (Cole et al., 1973).Spiroplasma citri was isolated and characterized by Saglio et al. (1973) and is the leafhopper-transmitted agent of little-leaf disease of citrus (Markham et al., I 974). We have isolated a pathogenic strain of S. citri, which lacks the characteristic helical morphology, from diseased citrus material. M E T H O D SIsolation and culture. A non-helical spiroplasma and six normal strains of S. citri were isolated from 'lop-sided' fruits of little-leaf diseased sweet orange trees by the method of Daniels et al. (1973). Isolates were subcultured twice in complete sorbitol medium (SMC; Saglio et al., 1973) without arginine and tryptone, before 0.1 ml samples were plated on SMC solidified with I % (w/v) agar (Oxoid no. I). After incubation for 7 days at 32 "C, colonies showing unusual morphology were picked off into SMC medium. One of these isolates was cloned three times and designated ASP-I. All cultures were maintained in SMC at 32 "C. Characterized strains of S. citri ~8 -~2 (type strain) and c189 were kindly supplied by Dr P. Saglio, and the pathogenic strain SP-A was isolated in this laboratory (Daniels et al., 1973).Media and incubation conditions. The colony and cell morphologies of strains SP-A and ASP-I were compared under different conditions. Plates of SMC solidified with 0.75 % and I % (wlv) agar were spread with 0-1 ml of diluted spiroplasma culture and incubated at 32 "C for 7 days in air or in N2/C02 (95 : 5, v/v). Cultures in SMC were incubated at 25, 28, 2 M I C 100

Totipotent leaf mesophyll protoplasts of Nicotiana plumbaginifolia, Viviani were inoculated with cassava latent virus (CLV) or with full length copies of CLV genomic DNAs 1 and 2 excised from replicative forms of M13 clones. Virus specific DNAs began to appear 48-72h after inoculation with virus or cloned DNAs, coincident with the onset of host cell division. Infected cells accumulated supercoiled forms of DNAs 1 and 2 as well as progeny single-stranded (ss) virion (+) sense DNAs representing each component of the genome. Both supercoiled and ss molecules were synthesised by cells inoculated with cloned DNA 1 alone but DNA 2 failed to replicate independently.