Lettuce, in its cultivated form (Lactuca sativa L.), is a crop of economic importance with several characteristics which make it well suited for biochemical and genetic studies. Biochemical traits such as proteins and enzymes have been studied extensively in many plant species and constitute an important experimental approach to physiological, evolutionary, taxonomic and breeding studies. Seed proteins were extracted from an array of lettuce cultivars. Polyacrylamide gel electrophoresis was employed in a comparative analysis of the soluble protein and isozyme characteristics of seed from each cultivar. Some fall-desert, winter-desert, and coastal cultivars were distinguishable based upon variation in soluble proteins or esterase isozymes. Multiple forms of the carboxylic ester hydrolases or esterases have been shown to occur in a wide variety of plants; their role in the plant cell is still however poorly understood. The inheritance of the esterase isozymes was analyzed by a microelectrophoresis technique which enabled the analysis of individual seeds in the progeny from a cross involving two winter-desert cultivars of contrasting banding phenotypes. Two distinct banding patterns were observed in single seeds of these cultivars; their F₁ hybrid showed a summation of parental patterns, the F₂ segregated in a 1:2:1 phenotypic ratio for these esterase patterns, and backcross segregation ratios were 1:1. Banding pattern differences could be accounted for by the segregation of a single gene with codominant action. Quantitative as well as qualitative differences in esterase activity were observed between the parental lines from two different years of production. Some esterase isozymes were developmentally regulated. Molecular weight determination experiments verified the presence of two gene products of 56 and 62.5 Kd.

Bibliography: leaves 143-150. / xxii, 150 leaves : col. ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Isozyme analysis was carried out on sweet cherry (Prunus avium) leaves. Cultivars were identified and compared. Progeny from controlled hybridisations were examined to determine inheritance patterns of isozymes. Isozymes were also used to determine gene flow in cherry orchards and to determine pollen donors of selected cultivars. / Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, (1996?)

Includes bibliographical references

Giardia lamblia, an enteric protozoan parasite, infects a large number of individuals worldwide. In South Africa prevalences ranging between 4 and 63% are documented, however, the impact of giardiasis is underreseached in this country. Giardia infections vary from asymptomatic carriage or a self-limiting acute symptomatic illness to chronic, debilitating malabsorption syndrome. The factors responsible for development of symptomatic versus asymptomatic infection are poorly understood. It is believed by some that host factors determine the clinical outcome of infection. On the other hand, the possibility of the existence of pathogenic and non-pathogenic strains (a situation akin to Entamoeba spp.) remains to be explored. One requirement for investigation of the potential contribution of strain differences to pathogenecity of infection is establishment of laboratory cultures of different strains isolated from symptomatic and asymptomatic patients. The present study was undertaken to develop and modify existing methods for: (i) establishment of laboratory cultures of Giardia trophozoites from excystation of faecal cysts, (ii) long-term maintenance and cryopreservation of the cultures and (iii) preliminary characterisation methodology. One thousand and twenty-three stool specimens were collected from day care centres, hospital wards and Hlabisa hospital laboratory. A further 6246 were retrieved from the Microbiology Laboratory at King Edward VIII Hospital and screened by direct wet preparation. Giardia was detected by light microscopy following formol-ether concentration (127 of 1023 samples) or direct examination of wet preparations (78 of 6246 samples). Cysts were purified from the positive specimens by sucrose gradient separation. Viability was assessed by a dye-exclusion method (eosin). Three in vitro excystation techniques were employed in an attempt to obtain trophozoites for initiation and establishment of viable cultures thereof. Culture conditions were optimised using two reference strains of Giardia, WB & H7 (obtained from the National Institutes of Health, USA). The percentage excystation ranged between 0-42% with all the in vitro methods of excystment. Excysted trophozoites remained viable in TYI-S-33 culture medium for periods ranging between 12-72 hours or up to 9 days, and gradually died, hence viable trophozoite cultures could not be established. Some culture initiates (overall 65%) were lost through overwhelming bacterial and!or fungal contaminants. An animal model was subsequently set up in which C57BL/6 and Praomys (Mastomys) coucha mice were used for in vivo excystation experiments. 1-3 day old suckling mice were intragastrically injected with 10,5 -cysts/ ml in 0,1 ml distilled water. Trophozoites were retrieved from the stomachs of infected mice 7-10 days after inoculation and cultivated in TYI-S-33 medium. Six local isolates were axenised using the in vivo excystation method. They have been maintained for more than 15 months in culture after stabilates and Iysates of confluent growths had been cryopreserved in Liquid Nitrogen. Successful (100%) retrieval of the cryopreserved cultures has been achieved. Seven isoenzyme electrophoresis systems have been set up and optimised. Reproducible results were obtained in six of the enzymes. Some differences in banding patterns of the enzymes were demonstrated. / Thesis (M.Med.Sc.)-University of Natal, Durban, 1999.