The methylation status of DNA derived from potato plants recovered from slow growth

The in vitro conservation of potato using tissue culture medium supplemented with the growth retardant mannitol causes morphological changes in the propagated material. These culture conditions seem to have an affect on the DNA extracted from the regenerated plants, when it is digested by the methylation sensitive restriction enzymes Hpa II/Msp I and Eco RII/Bst NI, compared to the control material. In most of these plants, there appears to be preferential methylation of nuclear domains that contain Eco RII/Bst NI recognition sites in contrast to those that contain Hpa II/Msp I sites. The refractory nature of the isolated DNA to these restriction enzymes was attributed to hypermethylation of genomic DNA and the ribosomal RNA genes. These findings indicate that methylation of DNA sequences may be an adaptive response to conditions of high osmotic stress. The importance of these results for the conservation of potato germplasm and international exchange is discussed.     

The evolutionary origin of the 35 kb circular DNA of Plasmodium falciparum: new evidence supports a possible rhodophyte ancestry

In common with other Apicomplexan parasites, Plasmodium falciparum carries two extrachromosomal DNAs, one of which, the 6 kb element, is undoubtedly mitochondrial. The second, generally referred to as the 35 kb circle, is of unknown provenance, but the nature and organization of its genetic content makes a mitochondrial association unlikely and the molecule has features reminiscent of plastid genomes. We now report the occurrence on the circle of an open reading frame specifying a predicted 470 amino acid protein that shares more than 50% identity with a gene currently known only on the plastome of red algae. This high degree of conservation confirms the 35 kb circle's plastid ancestry, and we speculate that it may have originated from the rhodoplast of an ancient red algal endosymbiont in the progenitor of the Apicomplexa.     

A minichromosome-like structure in wheat embryos

A crude nuclear fraction of resting wheat embryos was used as the source of putative plant minichromosomes: unique DNA sequences the size of genes and flanked by telomere-type repeats. Preliminary separation of low-molecular-weight DNA species from chromosomal DNA (Hirt's method), velocity sedimentation, and isopycnic centrifugation were followed by PCR amplification of minichromosome-like sequences. The most abundant PCR product was cloned and sequenced. In addition to telomeric repeats (defined by a PCR primer), which were the expected sequences, the linear DNA molecule (637 pb) contained an ARS-like element, RAP1-binding site, and two relatively long ORFs. The whole sequence seems to represent a naturally occurring plant minichromosome.     

Cytological and molecular characterization of a chromosome interchange and addition lines in Cadet involving chromosome 5B of wheat and 6Ag of Lophopyrum ponticum

Efforts to transfer wheat curl mite (Eriophyes tulipae Keifer) resistance from Lophopyrum ponticum 10X (Podb.) Love to bread wheat (Triticum aestivum L.) have resulted in the production of a number of cytogenetic stocks, including an addition line of 6Ag, a ditelo addition line, and a wheat-Lophopyrum translocation line. Characterization of these lines with C-banding, in situ hybridization with a Lophopyrum species-specific repetitive DNA probe (pLeUCD2), and Southern blotting with pLeUCD2 and a 5S ribosomal DNA probe (pScT7) confirmed that the distal portion of the short arm of 6Ag was translocated onto the distal portion of 5BS (5BL. 5BS-6AgS). It was also determined that the ditelo addition was an acrocentric chromosome of 6AgS.     

Multilocus DNA fingerprints in the plant Cynoglossum officinale L. and their use in the estimation of selfing

We have developed a nonradioactive oligonucleotide multilocus DNA fingerprinting method for Cynoglossum officinale . Of the 19 probes tested, six probes yielded banding patterns for all restriction enzymes used. All but one of the informative probes are repeats with a four-base motif. Approximately 60% of the loci appeared to be polymorphic. The sensitivity of the nonradioactive method was equal to that of the radioactive method. In addition, a new simple calculation method is presented to estimate selfing rates and approximate 95% confidence limits from the DNA fingerprint profiles avoiding 'between-gel' comparisons. The selfing rates differed significantly (as determined from 95% confidence intervals) between naturally pollinated individuals of C. officinale within the experimental population. The estimates ranged from 0 to 70% selfing.     

Multiple paternity in the red-eyed treefrog Agalychnis callidryas (Cope)

DNA fingerprinting of tadpoles from two different ‘one female-two male’ matings of the red-eyed treefrog, Agalychnis callidryas, revealed multiple paternity of offspring. Offspring were assigned paternity based on bands shared with the putative father, but not shared between putative fathers or with the mother. Paternity was split 44/56% and 36/64% in two matings. These results do not support a hypothesis of sperm priority in access to unfertilized eggs by primary males. Multiple paternity may be commonplace in species of anurans with matings by multiple males.     

Two cDNA clones coding for the legumin protein of Pisum sativum L. contain sequence repeats

The sequence of two cDNA clones coding for the whole of the -subunit and most of the -subunit of legumin are presented together with a considerable amount of protein sequence data to confirm the predicted amino acid sequence. A unique feature shown by these cDNAs is the presence of three 56 base pair tandem repeats in the region encoding the C terminal of the polypeptide. The tandem repeats are also exhibited in the predicted polypeptide sequence as three 18 amino acid repeats which contain extremely high proportions of polar, mainly acidic, residues. The new sequences are compared to the previously published sequence of some shorter legumin cDNAs (Nature 295: 76–79). In the region where the sequences overlap, the previous cDNAs differ from the new ones by only a few base substitutions but most of the repeated region is not present though the sequences on either side are. The possibility that the absence of the repeats may reflect the difference between two types of legumin gene, rather than an artefact of the cloning of the cDNAs, is discussed.     

Molecular and cytological characteristics of nuclear DNA and chromatin for angiosperm systematics: DNA diversification in the evolution of four orchids

The species- and genus-specific DNA content, average base composition of nuclear DNA, presence or absence of satellite DNA, the percentage of heterochromatin and other characteristics of nuclear DNA and nuclear structure allow to deduce the molecular changes which accompanied, or more probably caused, cladogenesis in the orchids studied. It is suggested that saltatory replication (generative amplification) of certain DNA sequenes, diversification of reiterated DNA sequences, and loss of DNA play an important role in the evolution of orchids.—The relationship between changes of genome composition and of nuclear structure and ultrastructure is discussed on the basis of cot curves, heterochromatin staining with Giemsa (C banding), electron microscopy of nuclei, and molecular hybridization in situ.Some aspects of this paper have been presented at the Helsinki Chromosome Conference, August 1977 (Nagl & Capesius 1977).