Analysis of the introgression of Solanum bulbocastanum DNA into potato breeding lines

Somatic hybrids have been obtained between potato and Solanum bulbocastanum PI 245310, a Mexican diploid (2n=2x=24) species. Through restriction fragment length polymorphism (RFLP) and randomly amplified polymorphic DNA (RAPD) analyses it was found that the somatic hybrids contain each chromosome of the diploid parent and that the synteny of RFLP markers noted with tomato, potato and S. brevidens is largely maintained in S. bulbocastanum. RFLP analyses of BC1 progeny of two different hybrids indicated that a substantial number of markers were either lost or were heterozygous, in marked contrast with results previously noted with S. brevidens. A RAPD map for all 12 chromosomes of S. bulbocastanum was prepared and marker transmission was followed in three BC2 populations. Results with chromosomes 3, 8 and 10 from these populations are compared.     

Cryomicroscopy of liposome sytems as simple models to study cellular freezing response

Liposomes represent an attractive model system to study the freeze/thaw-induced alterations in biological membranes primarily because liposomes may be custom-manufactured for a particular investigation.This paper has reviewed briefly the degree of flexibility possible in terms of manufacturing liposomes with desired membrane composition and intraliposomal markers.Earlier research using liposomes as a model to study the freezing response of biological cells demonstrated their usefulness in this respect. Combining these earlier results with new results obtained in our laboratory, many analogies between the responses of biological cells and liposomes have been demonstrated. These analogies are summarized in Table 3.It is significant to note that in virtually every category thus far examined the relevant cryobiological behavior of biological cells can be mimicked qualitatively (and in some cases quantitatively) by a pure lipid membrane system. This is not to say that protein components of the membrane are insignificant. They are likely to be quite important in some cases. The liposome model system offers some interesting possibilities of examining the relative importance of lipids and proteins in model systems.Cryomicroscopic observation of liposome systems represents a promising approach to an improved understanding of membrane-related phenomena which occur during freezing and thawing. Especially interesting are the observations of membrane instabilities (“popping”) which appear to be induced osmotically.Real-time observation of well-defined membrane bilayer systems subjected to computer-controlled freeze/thaw protocols should lead to valuable insights into the nature of membrane freezing injury in the future.     

Fragments of plastid DNA in the nuclear genome of tomato: prevalence, chromosomal location, and possible mechanism of integration

Summary We have undertaken a systematic search for plastid DNA sequences integrated in the tomato nuclear genome, using heterologous probes taken from intervals of a plastid DNA region spanning 58 kb. A total of two short integrates (202 and 141 nucleotides) were isolated and mapped to chromosomes 9 and 5, respectively. The nucelotide sequence of the integrates and that of the flanking regions were determined. The integration sites contain direct repeat elements similar in position (but not in length or sequence) to the direct repeats previously observed with another plastid integrate in the tomato nuclear genome. Based on these results, a model for the process of movement and integration of plastid sequences into the nuclear genome is discussed.