Plant Physiology 99:60-66 (1992)
© 1992 American Society of Plant Biologists
Metabolism and Enzymology
Regulation of Mitochondrial Function and Biogenesis in Cucumber (Cucumis sativus L.) Cotyledons during Early Seedling Growth 1
Steven A. Hill2,
Christopher P. L. Grof,
James H. Bryce and
Christopher J. Leaver
Department of Botany, University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh EH9 3JH, United Kingdom,
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RA, United Kingdom,
Department of Biological Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, United Kingdom
The aim of this work was to characterize the respiratory metabolism of the greening cotyledons of cucumber (Cucumis sativus L.) during early seedling growth and to investigate how this is integrated with changes in mitochondrial biogenesis and function. In light-grown cotyledons, lipid mobilization extended from germination to 6 days postimbibition, reaching a maximum at 3 to 4 days postimbibition. The rate of dark oxygen uptake reached a maximum at 2 days postimbibition in dark-grown and 3 days postimbibition in light-grown cotyledons. Development of photosynthetic capacity occurred from 4 to 7 days postimbibition. In dark-grown cotyledons, lipid mobilization extended beyond 7 days postimbibition, and there was no greening or acquisition of photosynthetic competence. Measurements of mitochondrial function indicated that the respiratory capacity of the tissue changed such that during lipid mobilization there was a much greater capacity for the operation of the nondecarboxylating portion of the citric acid cycle (succinate to oxaloacetate), whereas during the development of photosynthetic function the activity of the remainder of the cycle (oxaloacetate to succinate) was induced. Comparison of the maximum capacities for mitochondrial substrate oxidations in vitro with the rates of in vivo substrate oxidations, predicted from the rate of lipid breakdown, indicated that mitochondria in this tissue operate at or below state 4 rates, suggesting limitation by both availability of ADP and substrate.
2 Present address: Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
1 This research was supported by the Gatsby Charitable Foundation (Sainsbury research studentship to S.A.H.) and the Agriculture and Food Research Council (grant No. PG43/516 to C.J.L.).
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