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United States Department of Agriculture

Agricultural Research Service

Title: Where Do All the Electrons Go after a Chill? Estimating the Size of the Chloroplast Mehler-Ascorbate Peroxidase (Water-Water) Flux

item Allen, Damian
item Ort, Donald

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 2, 2001
Publication Date: N/A

Technical Abstract: Analyses of relative rates of photosystem II electron transport with CO2 uptake frequently imply that chilling leads to an increase in alternative, non-CO2, electron sinks. It has been argued that exploiting oxygen as a terminal electron acceptor, in both Rubisco oxygenase photorespiration and Mehler-ascorbate peroxidase (APX) pathway, protects plants from photodamage in bright light. Thylakoid electron transport is intrinsically vulnerable to producing active oxygen species. To prevent calamitous damage to component proteins and lipids, plants have numerous antioxidant systems. Regeneration of these antioxidants, by Mehler-APX cycle, may be an important and variable electron sink. To date quantification of this sink has utilized the addition of **18O2 to a leaf and a mass spectrometer to differentiate the **18O2 uptake fluxes from that of **16O2 PSII evolution. These are not steady-state measurements and require expensive equipment. Only 8 of the 104 most recent papers discussing this reaction actually measured its flux. We describe the simultaneous use of a new high resolution differential O2 analyzer with steady-state leaf CO2 and H2O gas exchange and chlorophyll fluorescence. This provides a simple method to quantify the size of O2 sink for electrons, and determine whether the Mehler-APX cycle is the major additional sink for electrons observed following a chill.

Last Modified: 4/22/2015
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