School of Botany - Theses

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    Role of Ribulose-1,5-Bisphosphate Carboxylase
    Kelly, Michael (Michael Ernest) (University of Melbourne, 1998)
    Physiological adaptations by plants in order to better utilise sunflecks were studied using plants from the rainforest understorey. Transgenic Rubisco and wild-type Nicotiana tabacum L., from the Solanaceae family, were used to model these adaptations and to better characterise the light induced activation kinetics. Tobacco plants with varying Rubisco concentrations were used to obtain plants with differing Activase to Rubisco stoichiometry. An increase in the stoichiometry caused proportional changes in the rate of Rubisco activation. This was reflected in a decrease in the relaxation times from 2.5 to 3 minutes down to 35 to 40 seconds. This faster rate of activation lead to a reduction in the amount of C02 assimilation effectively forgone due to the activation process. In wild-type tobacco this amount of forgone photosynthesis was found to be, on average, 23.5 ?mol C02 m-2 compared to 6.0 ?mol C02 m-2 for Rubisco mutant tobacco plants. Understorey plants from the rainforest of Cape Tribulation National Park (QLD) were examined to see if they adjusted their stoichiometry of Activase and Rubisco in order to increase C02 assimilation in sunflecks. Gas exchange analysis of the rainforest plants showed them to behaved in a similar fashion to the Rubisco mutant tobacco. Examination of the kinetics of Rubisco activation in rainforest and Rubisco mutant tobacco plants found, on average, comparable relaxation times (58 and 67 seconds, respectively) and similar initial activation rates (46.6 and 46.1 nmol active sites m-2 s-1, respectively). When compared to wild-type tobacco, the rainforest plants on average were found to have over 5.5 times the ratio of Activase to Rubisco. This leads to a reduction in the average amount of forgone photosynthesis from 23.5 ?mol C02 m-2 for wild-type to 4.2 ?mol C02 m-2 for rainforest plants. These results suggest that plants grown under fluctuating light environments alter their stoichiometry in order to better utilise sunflecks for carbon gain.
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    Collected papers submitted for the degree of Doctor of Science in the University of Melbourne
    Neales, Tom Finnis. (University of Melbourne, 1978)
    The two major themes of this thesis of published work reflect my interest in the function of the trace element boron in plant nutrition and also my later, and present, involvement with the whole-plant aspects of photosynthesis and carbon nutrition, including that of crop species. In the 1950's there was,in Australia, great interest in the plant physiology of the plant trace elements - Mn, Zn, Cu, Mo and B. This interest derived from the findings of the 1940's that the correction of trace element deficiencies (in plants, cattle and sheep) increased agricultural production in existing pastoral areas, and also allowed hitherto unproductive regions to be cultivated (see, Anderson, 1971 and Underwood, 1962). My interest in the function of boron in plant nutrition originated under these influences in 1956, when I arrived in Melbourne University on an appointment whose brief was to teach plant and crop physiology to Agricultural Science students. This research interest widened in the early 1960 ' s in include aspects of the photosythetic and gas-exchange behaviour of leaves and intact plants. This was prompted by several influences including an interest in the physiological aspects of crop production and plant adaptation, the horizons that were opened by Gaastra's (1959) pioneering paper, and the availability of infrared absorption instruments (IRGAs) that allowed the accurate and instantaneous measurement of carbon dioxide and water vapour in an air stream. These involvements were much stimulated by the, initially apparently disparate, work of the 1960's on the physiology and biochemistry of photosynthesis in which some intellectual coherence was achieved in 1969-1970. This was the realisation that there existed in plants at least three distinct 'modes' of photosynthesis - C^, C4 and CAM (see: Bj�rkmann, 1973). My continuing association with Agricultural Science, and with its students and problems, also lead to work in crop physiology, mainly using the ideas and techniques associated with the investigation of photosynthesis and growth.