Tea (Ozmellia sinensis) aroma is tmderpinned by two stresses, withering and wounding, which are part of the tea manufacturing process. A cross-species approach has been employed, where the tea DNA was hybridised to the Affymetrix ATHI chip, which extended coverage beyond Unilever's 3()(X) tea-gene rnicroarray to a potentia118,509 probes. This filter was then used for subsequent microarray analyses of both a factory trial. and a more robust laboratory trial. The observed changes in gene expression were consistent with the stress responses, adding confidence to the cross-species approach. The same RNA samples were used on the Unilever Agilent microarray as a comparison, and found that both platforms followed a similar trend, though there were too many ambiguities to draw firm conclusions. Arabidopsis drought and wounding microarray datasets were analysed and compared with the tea data, revealing a set of 90 core genes both conserved between species and common to the two stresses. The mapping of the microarray data onto KEGG pathways was informative in terms of aroma metabolism, however this was limited. This prompted the merging of Arabidopsis protein interaction, gene regulatory, coexpression and metabolic networks as a way to increase our understanding of the interactions taking place in Arabidopsis and tea. Firstly, a network was filtered based on the sets of core genes. This revealed that in Arabidopsis the lipoxygenase path• way (to hexenol and jasmonate) and 4-cownerate ligase (of phenylpropanoid pathway) appear to be regulated by the same mechanism, as they have well correlated coexpression across NASCArrays. Their high-level expression in tea suggests they may be coregulated in this plant as well. Other aspects of stress mediated gene regulation and cell Signalling were also uncovered. The merged network was also filtered for genes with GO-terms for "response to stress" and "aroma metabolism", and revealed further connections between parts of the processes linking stress with aroma metabolism. nus PhD has used transcriptomics linked with network biology as a way for us to understand tea withering and wounding, and generated a resource for further investigation of the links between stress and tea metabolism. This could be applied to flavour, colour and the stimulatory effects of tea.

Thesis (M.Sc. (Horticulture)) --University of Limpopo, 2007 / Bush tea (Athrixia phylicoides DC) has been used for many years by the people of South Africa for medicinal purposes. The herbs was only harvested from the wild, therefore data on the effects of mineral nutrition on total antioxidant activity had not been established. The objective of this study was to determine the seasonal effect of nitrogen (N), phosphorus (P) and potassium (K) nutrition on total antioxidant activity (TAA) in cultivated bush tea leaves. Treatments consisted of 0, 100, 200, 300, 400 or 500 kgha-1 N, P or K in a randomized complete block design with four replications under 50 % shade nets. Three (N, P and K) parallel trials were conducted per season (autumn, winter, spring and summer). TAA was determined using 2,2-diphenyl-1-picrylhydrazyl-hydrate (DPPH) method and analyzed in a spectrophotometer. Results of this study demonstrated that regardless of season, the application of N, P and K fertilizers increased quadratically levels of TAA in bush tea with most of the increase occurring between 0 and 300 N, 300 P and 200 K kgha-1. Therefore, for improved total antioxidant content in bush tea leaves, 300 N, 300 P and 200 K kgha-1 N are recommended. / National Research Foundation (NRF), Agricultural Research Council(ARC-LNR)