SummaryPlant transformation via Agrobacterium frequently results in formation of multiple copy T-DNA arrays at one target site of the chromosome. The T-DNA copies are arranged in repeats, direct or inverted around one of the T-DNA borders. A Ti plasmid-derived transformation vector has been constructed enabling direct selection of transformants carrying at least two linked copies of T-DNA in the same orientation. The selection is based on expression of a promoterless neomycin phosphotransferase gene on one T-DNA copy from a promoter located on the other T-DNA copy. After co-cultivation of tobacco protoplasts with Agrobacterium, as many as 30% of regenerated transformed plants carried directly repeated T-DNA copies. The junction regions between two T-DNAs were amplified and 13 amplified fragments were cloned and sequenced. The involvement of T-DNA left and right border sequences in direct repeat junctions was determined. In some junctions, additional filler DNA was detected. The length of filler DNA varied from a few up to almost 300 bp. The longer filler DNAs from two clones were found to be T-DNA fragments in direct or reverse orientation. We discuss the recently suggested models for T-DNA integration and propose that the formation of direct repeats in genomes does not necessarily result from ligation of intermediates (i.e. T-strands), but more likely from the co-integration of several intermediates into one target site.

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To overcome low, genotype dependent regeneration capacity of some commercially important potato cultivars, two alternative treatments of stem primary explants were employed: modification of the hormonal composition of inductive MS medium and insertion of some Agrobacterium oncogenes. A replacement of 6-BAP with zeatin in the inductive MS medium stimulated bud/shoot formation in only two of three tested cultivars with naturally low regeneration capacity. GA 3 did not affect the bud initiation phase (i.e. regeneration capacity of cultivars), it only stimulated shoot development. The insertion of some bacterial oncogenes (in particular genes 4, rolB, C and 5) enhanced bud/shoot formation, especially in the case of low-regenerating cultivars.

Dactylaria pyriformis Juniper and Dactylaria thaumasia Drechsler are predacious fung forming three-edimensional sticky reticula in which nematodes are captured. It was shown by methods developed in our laboratory that in submerged cultivations both of these fungi produce substances attracting nematodes and compounds having nematicidal activity.

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