Introduction, maintenance and utilization of male sterility in leek (Allium ampeloprasum L.) = [Inductie, handhaving en gebruik van mannelijke steriliteit in prei (Allium ampeloprasum L.)]

This thesis describes research work performed in leek in relation to efforts to obtain or exploit a male sterility system for hybrid leek breeding. Male sterile plants can be found in every leek cultivar. The male sterility trait can be explained by a nuclear monogenic inheritance or by a nucleo-cytoplasmic inheritance. The existence of a nucleo-cytoplasmic inheritance remains speculative unless the maintainer genotype will be identified. No source of CMS has been found, sofar, in leek or related forms of A. ampeloprasum L.Mutation breeding experiments during an extended period of time, using chemicals or somaclonal variation, did not result in the induction of cytoplasmic male sterile mutants in leek.The small chances for fixation of a mutation in a mitochondrial genome population and problems concerning the identification and recovery of the cytoplasmic mutation at the plant level may have been the major obstacles in obtaining a cytoplasmic male sterile mutant.An efficient callus regeneration system and the selection of leek plants with improved regeneration ability are described in this thesis. The availability of a regeneration system is an essential step in the application of somatic hybridization, somaclonal variation and transformation techniques in leek.Vegetative propagation of nuclear male sterile genotypes remains up till now the most realistic option for producing leek hybrids. A new in vitro method for mass clonal propagation of leek, based on flower stalk explants, was developed and is described in this thesis. This method offers a realistic opportunity to leek breeders for producing leek hybrids, until a less expensive genetic system for producing male sterile lines would become available

Matrix-Assisted Laser Desorption Ionization-Mass Spectrometry Signal Enhancement of Peptides after Selective Extraction with Polymeric Reverse Micelles

Extraction of peptides by reverse micelle-forming amphiphilic homopolymers and subsequent matrix-assisted laser desorption ionization-mass spectrometry (MALDI-S) detection of these peptides in the presence of these polymers can significantly enhance peptide ion signals. Here, the mechanism of this MALDI signal enhancement is investigated. We find that the signal enhancement is caused by coalescence of polymer-peptide conjugates into "hotspots" on the MALDI target. Hotspot formation is observed only on hydrophilic surfaces and not hydrophobic surfaces. With the use of an Anchorchip MALDI target, which contains very small hydrophilic spots surrounded by a larger hydrophobic area, we find that this hotspot formation can be further exploited for ultrasensitive MALDI-MS analyses of peptides and peptide mixtures. MALDI-MS signals can be enhanced by 3-5 orders of magnitude when peptides are extracted by the amphiphilic homopolymers and detected on the Anchorchip MALDI target. This signal enhancement combined with the extraction selectivity of these reverse micelle-forming homopolymers makes these materials promising tools for sensitive detection of peptides in complex mixtures