Rubisco in planta kcatis regulated in balance with photosynthetic electron transport
Site turnover rate (k cat ) of Rubisco was measured in intact leaves of different plants. Potato (Solanum tuberosum L.) and birch (Betula pendula Roth.) leaves were taken from field-growing plants. Sunflower (Helianthus annuus L.), wild type (wt), Rubisco-deficient (–RBC), FNR-deficient (–FNR), and...
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Published in | Journal of experimental botany Vol. 60; no. 14; pp. 4077 - 4088 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Oxford University Press
01.01.2009
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Subjects | |
Online Access | Get full text |
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Summary: | Site turnover rate (k cat ) of Rubisco was measured in intact leaves of different plants. Potato (Solanum tuberosum L.) and birch (Betula pendula Roth.) leaves were taken from field-growing plants. Sunflower (Helianthus annuus L.), wild type (wt), Rubisco-deficient (–RBC), FNR-deficient (–FNR), and Cyt b 6 f deficient (–CBF) transgenic tobacco (Nicotiana tabacum L.) were grown in a growth chamber. Rubisco protein was measured with quantitative SDS-PAGE and FNR protein content with quantitative immunoblotting. The Cyt b 6 f level was measured in planta by maximum electron transport rate and the photosystem I (PSI) content was assessed by titration with far-red light. The CO 2 response of Rubisco was measured in planta with a fast-response gas exchange system at maximum ribulose 1,5-bisphosphate concentration. Reaction site k cat was calculated from V m and Rubisco content. Biological variation of k cat was significant, ranging from 1.5 to 4 s -1 in wt, but was >6 s -1 at 23 °C in –RBC leaves. The lowest k cat of 0.5 s -1 was measured in –FNR and –CBF plants containing sufficient Rubisco but having slow electron transport rates. Plotting k cat against PSI per Rubisco site resulted in a hyperbolic relationship where wt plants are on the initial slope. A model is suggested in which Rubisco Activase is converted into an active ATP-form on thylakoid membranes with the help of a factor related to electron transport. The activation of Rubisco is accompanied by the conversion of the ATP-form into an inactive ADP-form. The ATP and ADP forms of Activase shuttle between thylakoid membranes and stromally-located Rubisco. In normal wt plants the electron transport-related activation of Activase is rate-limiting, maintaining 50–70% Rubisco sites in the inactive state. |
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ISSN: | 0022-0957 1460-2431 |