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    Physiological aging in taewa Māori (Māori potatoes, Solanum tuberosum) and the suitability of different cultivars for short season cropping : a thesis in partial fulfilment of the requirements for the degree of Master of Agriscience in Horticulture at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Hutchins, Daniel
    Altering the storage regime of potato (Solanum tuberosum) seed tubers alters the performance of crops grown from those tubers. The size and nature of these effects are cultivar specific. Potato seed tubers progress through a number of stages during storage, a process known as physiological aging. The rate of aging is affected by many factors the most significant of which is the amount of warming (thermal time) the seed is exposed to during storage. Having seed tubers of an appropriate age can increase early crop growth and improve early yields. With the recent establishment of the Tomato-Potato Psyllid (Bactericera cockerelli, TPP) in New Zealand, shorter growing seasons have become desirable, as ongoing costs of controlling TPP on potatoes and other crops are significant. Taewa Māori (Māori potato; Solanum tuberosum ssp. tuberosum & andigena) have been grown in New Zealand for over 220 years and have developed into a range of potato cultivars unique to New Zealand. Taewa hold significant cultural value and are part of the story of early colonial New Zealand. Seed tubers from three cultivars of taewa, Moemoe, Kowiniwini and Waiporoporo, were exposed to different periods of warming (thermal time, degree-days) prior to planting. All three cultivars displayed some level of resistance to the effects of physiological aging over the range of thermal time studied. However some effects were observed. There was an increase in tuber number with an increased thermal time in the cultivar Moemoe, but no change in tuber fresh weight in any treatment. The tuber dry matter in Waiporoporo was highest in tubers exposed to 728 degree- days indicating there may be an optimal amount of degree-days in terms of this parameter. The resistance of these taewa to physiological aging means growers might save on cool-storage costs by reducing storage time. The early harvests and physiology of the three cultivars were assessed for their suitability to a short (90 day) season. The cultivar Waiporoporo showed the best yield characteristics for a table potato crop over a 90-day season. Waiporoporo set fewer tubers than the other two cultivars but the tubers it produced were larger and more suited to the table market. Waiporoporo had a higher tuber fresh weight than Kowiniwini and greater leaf area than Moemoe at 90 days after planting (DAP). Moemoe showed the best potential in terms of the salad potato, new potato and gourmet markets that require smaller tubers than the table market. Taewa growers looking to shorten their cropping season should consider using the cultivar Waiporoporo for the table market, and Moemoe for markets that require smaller potatoes.
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    Phytochemical-rich potato extracts and potential for risk reduction in tamoxifen treatment of breast cancer : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Chong, Esther Swee Lan
    Existing data suggest an inverse correlation between breast cancer risk and vegetable consumption, and the anticancer effects of vegetables are attributed to the diversity and abundance of phytochemicals. Standard endocrine therapies for breast cancer are associated with significant side effects and not always effective. Undoubtedly, there is a need for improved treatment of breast cancer. In the quest for better breast cancer treatments with fewer side effects, food and nutrition represent a logical strategy to explore. Potato (Solanum tuberosum L.) was chosen for the present project as the target vegetable for investigation. Pigmented potato has recently attracted research attention because of its potential health benefits. Two potato extracts were prepared from a white and purple variety (‘Urenika’) and referred to as WPE and PPE respectively. Tamoxifen and estradiol exhibited paradoxical effects: each of them was inhibitory at high doses but stimulatory at low to moderate doses, on proliferation of two breast cancer cell lines, MCF-7 and T-47D. In contrast, both PPE and WPE inhibited cell proliferation in a dose-dependent manner without paradoxical effects. The potato extracts also blocked estradiol- or tamoxifeninduced cell proliferation of these two cell lines. These findings imply that both potato extracts may have a role to play in prevention of breast cancer, or complementing tamoxifen to achieve desirable treatment efficacy. Since both PPE and WPE were equivalent in efficacy, one (PPE) was selected for further study, given the intention of developing a nutraceutical or therapeutic product of New Zealand proprietary value. Phytochemical compositions of the potato extracts were identified and quantified using ultra high performance liquid chromatography-mass spectrometry, many of which were reported for the first time in variety ‘Urenika’. Several compounds were found at doses which have been reported individually to exert bioactive effects against cancer. It is possible the antiproliferative effects of potato extracts resulted from more than one of these bioactive compounds working together. Dose-dependent apoptotic effects of PPE were observed in T-47D culture, and a combined effect seems to exist between PPE and tamoxifen in modulating the S and G2/M phase. In summary, the key contributions and significance of current thesis are: (1) demonstration of the “risk” zone for tamoxifen (10-8 to 10-6 M) and estradiol (10-10 to 10-8 M) concentrations which may stimulate breast cancer cell growth. Note that these concentrations of tamoxifen or estradiol are physiologically achievable. Furthermore, one key novel finding is regarding the estradiol dependency of tamoxifen action. Specifically, at low to moderate doses (10-9 to 10-8 M) of tamoxifen, there is a threshold of estradiol (> 10-8 M) which allows a significant inhibitory action to occur. The stimulatory action of tamoxifen and complex interaction between tamoxifen and estradiol observed in vitro may partially explain the failure of tamoxifen treatment in some patients. Owing to the vast differences between cell culture experiments and the human body, a more systematic in vivo investigation of clinical effects of tamoxifen over a range of different doses under various estradiol concentrations is warranted; (2) pioneering data on the efficacy of ‘Urenika’ extract against breast cancer in vitro; (3) a metastatic breast cancer animal model which successfully generated metastasis to distant sites (lymph nodes, lungs, livers and spleens), mimicking advanced stage of breast cancer in humans. This model could be used in future testing of the effect of PPE and the combined treatments (PPE with tamoxifen) on establishment and metastasis; and (4) a ‘refined’ non-invasive feeding methodology, which is more ethical than oral gavages, for tamoxifen administration in mice was developed and results obtained were comparable to the method of intraperitoneal injection. Using this model and the non-invasive feeding method, a dose-dependent stimulatory effect of tamoxifen on growth of 4T1 tumours was observed in mice. The current thesis has derived a new hypothesis which may be worth clinical investigation: tamoxifen may induce excessive leukocytosis which contributes to tumour invasiveness and growth. This thesis also represents a significant contribution to the potential use of potato extracts in reducing the risk of tamoxifen in stimulating cancer growth.