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Regeneration of cucumber plants from leaf explants resulted in a new species phenotype designated mosaic (msc). It is characterized by two types of spots on the leaves (zucchini-like and chlorophyllous) and has many altered morphological and physiological properties including slower growth, smaller organs, poorly germinating or empty seeds and a smaller number of flowers per node. In msc plants the shape of the first leaf is always altered, and in about 76% of the flowers the crown is reduced and distorted to a varying degree. Chloroplasts of the zucchini-like sectors are filled with large starch grains, and some of the embryos die at various stages of development. The msc phenotype is transmitted uniparentally only by the male plant and no segregation is observed in the F2 and subsequent generations. Possible mechanisms responsible for the msc phenotype and its transmission are discussed.
Somaclonal variation commonly occurs during in vitro plant regeneration and may introduce unintended changes in numerous plant characters. In order to assess the range of tissue-culture-responsive changes on the biochemical level, the metabolic profiles of diploid and tetraploid cucumber R₁ plants regenerated from leaf-derived callus were determined. Gas chromatography and mass spectrometry were used for monitoring of 48 metabolites and many significant changes were found in metabolic profiles of these plants as compared to a seed-derived control. Most of the changes were common to diploids and tetraploids and were effects of tissue culture. However, tetraploids showed quantitative changes in 14 metabolites, as compared to regenerated diploids. These changes include increases in serine, glucose-6P, fructose-6P, oleic acid and shikimic acid levels. Basing on this study we conclude that the variation in metabolic profiles does not correlate directly with the range of genome changes in tetraploids.
A study was designed to obtain hapolid and double haploid (DH) plants from cucumber cultivars tolerant to Pseudoperonospora cubensis. The main goal was to identify RAPD molecular markers associated with downy mildew resistance. On average, 20% of embryos generated in two experiments, were converted to haploid plants. RAPD markers that differentiated susceptible and resistant H and DH plants were identified. Somaclonal variation in DH lines was seldom detected.
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