This project investigated a molecular strategy for the improvement of buffel grass (Cenchrus ciliaris) pastures with respect to digestibility. In other pasture plants, reduced lignin content has been associated with greater digestibility (Cherney et al, 1991). The isolation of appropriate target genes in the lignin biosynthetic pathway and development of a gene transfer system are two requirements for genetic manipulation of lignification in buffel grass. Work described in this thesis contributes to these research goals. A peroxidase catalyses the last step in the synthesis of lignin and a reduction in the activity of this enzyme should result in altered lignification. However, peroxidases constitute a multigene family. In addition to cell wall biosynthesis, they are involved in auxin catabolism, ethylene biosynthesis, chlorophyll catabolism, phenol oxidation and defence and wound healing responses (Campa, 1991; van Huystee, 1991; Walter, 1992). The first part of this work involved the isolation and characterisation of peroxidases from buffel grass. A cDNA library was constructed and screened with a peroxidase cDNA from wheat, WIR3 (Schweizer et al, 1989) and an oligonucleotide derived from a conserved region of plant peroxidases. Nine cDNA clones showed sequence homology to plant peroxidases in the GenBank and EMBL databases (Chapter 2). Two full length cDNA clones derived from different genes, PX7 and PX18, were completely sequenced (Chapter 3). They contained the characteristic features of peroxidases and have between 38% and 77% total amino acid homology to other plant peroxidases. All available plant peroxidase sequences in the databases were compared in an investigation of potential structure-function relationships. However, biological roles need to be ascribed to the cloned genes before a valid grouping can be justified (Chapter 3). A peroxidase involved in developmental lignification would typically be abundantly expressed in stem tissue and not show a wound response. With this in mind, a preliminary investigation of the expression characteristics of several cloned buffel grass peroxidases was undertaken (Chapter 4). The peroxidases encoded by PX7, PX18 and PX39 were expressed preferentially in leaves and a wound response was detected for PX35, PX39 and to a lesser degree for PX7. This preliminary characterisation suggests that these clones probably are not involved in developmental lignification and more buffet grass peroxidases need to be isolated and characterised. Microprojectile bombardment was investigated as a means of genetic transformation. This required the development of a tissue culture system for buffet grass that was amenable to both transformation and plant regeneration (Chapter 5). Embryogenic callus was initiated from surface sterilised mature seeds of buffet grass when cultured on Murashige and Skoog's nutrient medium supplemented with 3% sucrose, 5% coconut water and 4 mg 1-1 2,4-D. Shoots regenerated on 20% to 50% of embryogenic calli after transfer to hormone-free medium and incubation in the light. The ability to regenerate shoots was lost after approximately 20 weeks in culture. This frequency may be limiting for recovery of transgenic plants following particle bombardment. Conditions were readily established for gene transfer by particle bombardment into this callus type. These conditions yielded up to several hundred transiently expressing cells per bombardment. This is a promising system for production of transformed buffel grass plants.