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Lookup NU author(s): Professor Howard Griffiths,
Dr Wendy Elizabeth Robe,
Emerita Professor Anne Borland
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The diurnal regulation of Rubisco was compared for a range of crassulacean acid metabolism (CAM) species in the context of high carboxylation and electron transport capacities, which may be an order of magnitude greater than rates of net CO2 uptake. Early in the light period, Rubisco activity and electron transport were limited when phosphoenolpyruvate carboxylase (PEPC) may have been operating, and maximal extractable activities and activation state for Rubisco were achieved at the end of Phase III, prior to the direct atmospheric uptake of CO2 during Phase IV. The delayed activation was associated with levels of Rubisco activase protein, which reached a maximum at midday, and may account for this pattern of Rubisco activation. This regulation may be modified by environmental conditions - processes that tend to restrict PEPC activity, such as drought stress or incubation of leaves overnight in an oxygen-free atmosphere, release Rubisco from inhibition early in the light period. The quantum yield of light use also tracks Rubisco carboxylation, being particularly low at dawn when PEPC is active. The plasticity in expression of the CAM cycle is therefore matched by the regulation of key carboxylases, with extractable Rubisco activity maximal when drawdown of atmospheric CO2 to cells in succulent CAM tissues is most likely to limit photon utilization shortly after midday, during Phase IV.
Author(s): Griffiths H, Helliker B, Roberts A, Haslam RP, Girnus J, Robe WE, Borland AM, Maxwell K
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: Functional Plant Biology: 3rd International Congress on Crassulacean Acid Metabolism
Year of Conference: 2002
Publisher: CSIRO Publishing
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