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Sexual reproduction in flowering plants involves the production of male and female gametes crucial for successful fertilisation, yet molecular mechanisms in these processes are largely unknown. The goal of the research presented in this thesis is to understand more about these mechanisms. A novel pollen division mutant, duo pollen 4 (duo4), that fails to produce twin sperm cells was investigated. Genetic analyses revealed that duo4 acts post-meiotically and does not affect female gametophyte development. The majority of duo4 germ cells complete DNA replication and fail to enter mitosis, but mutant germ cell appears to differentiate normally when crossed to different cell fate markers. Map-based cloning defined the DUO4 locus to a 14.5 kb region containing the Cdh1/Fzr/Ste9- related, APC activator gene, CCS52A1. Molecular genetic approaches were combined to identify the cause of the germline defects in duo4. Gene expression analysis, misexpression and RNA interference (RNAi) experiments indicate that the duo4 phenotype results from misexpression of CCS52A1 in the male germline. This is persuasive evidence that CCS52 activity is subject to tight control during male germ cell cycle progression. DUO1 is a major transcription regulator of germ cell division and differentiation and the second major objective describes the validation of four native target genes in the DUO1 regulatory network. These target genes encode metabolic and transport-related proteins. The activity of these promoters was shown to be DUO1-dependent in the male gametophyte or the male germline, highlighting the importance of the DUO1 regulon in a range of functions required for sperm cell development. Collectively, these results advance understanding of how the male gametes are produced, and provide an improved molecular understanding of reproduction in higher plants.

Plant development continues post-embryonically throughout the life of the plant, and environmental conditions have a large influence on plant architecture and the timing of the switch from vegetative to reproductive growth. We could show that a key factor involved in transmitting environmental Information within the plant is FT. FT" is expressed in the leaf vasculature in response to floral inductive cues. FT protein is then transported through the vasculature to the shoot apex, where it builds an activating complex with the transcription factor FD to promote flowering. In this way FT expression provides temporal information, while the spatial information of where flowers are to be made is provided by the expression domain of FD.

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Rigorous control of ethylene inside storage atmosphere is cardinal to maintain quality of climacteric fruit, including avocado cv. Hass. This can be achieved using the ethylene action inhibitor, 1-methylcyclopropene (1-MCP). The recent development of a novel palladium (Pd)-based ethylene scavenger, e+® Ethylene Remover, provides a new opportunity to delay avocado fruit ripening. A new method was developed to sequentially extract and quantify both lipids and sugars from the same avocado mesocarp tissue sample. Extraction by homogenization with hexane yielded slightly less oil than the standard Soxhlet technique whilst the fatty acid profiles of the oil extracts were similar. Extraction of the resulting filter residue with methanol (62.5%, v/v) better recovered sucrose, perseitol and mannoheptulose as compared to ethanol (80%, v/v). The new method has a shorter extraction time, lower extraction temperature and requires less solvent. Presence of e+® Ethylene Remover in storage atmosphere removed all ethylene and accordingly delayed the ripening of avocado cv. Hass stored at low temperature. 1-MCP also inhibited ripening, yet, unlike e+® Ethylene Remover it impaired subsequent ripening. It was possible to slow down the ripening rate after the climacteric has been induced by removing ethylene below 1 μL L-1 in presence of e+® Ethylene Remover, and the scavenger was effective in combination with modified atmosphere packaging (MAP). Blocking ethylene action or removing ethylene did very slightly affect the fatty acid composition of the mesocarp oil. Depending on the origin and maturity of the fruit, 1-MCP and e+® Ethylene Remover better maintained seven-carbon sugars concentrations in mesocarp. Results support the view that mannoheptulose and perseitol could be important features of the avocado ripening process but more research is necessary to elucidate their exact function. Mesocarp abscisic acid (ABA) was quantified using a newly developed LC-ESIMS/ MS method. ABA increased as fruit ripened but appeared to be at least partly regulated by ethylene. Whether ABA influences the ethylene-associated ripening in avocado cv. Hass remains to be determined in future.