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Experimental and modelling data contradict the idea of respiratory down‐regulation in plant tissues at an internal [O 2 ] substantially above the critical oxygen pressure for cytochrome oxidase
Author(s) -
Armstrong William,
Beckett Peter M.
Publication year - 2011
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.2010.03537.x
Subject(s) - respirometer , alternative oxidase , respiration , respirometry , cytochrome c oxidase , oxygen , cytochrome , chemistry , biology , biophysics , biochemistry , botany , enzyme , organic chemistry
Summary• Some recent data on O 2 scavenging by root segments showed a two‐phase reduction in respiration rate starting at/above 21 kPa O 2 in the respirometer medium. The initial decline was attributed to a down‐regulation of respiration, involving enzymes other than cytochrome oxidase, and interpreted as a means of conserving O 2 . As this appeared to contradict earlier findings, we sought to clarify the position by mathematical modelling of the respirometer system. • The Fortran‐based model accommodated the multicylindrical diffusive and respiratory characteristics of roots and the kinetics of the scavenging process. Output included moving images and data files of respiratory activity and [O 2 ] from root centre to respirometer medium. • With respiration at any locus following a mitochondrial cytochrome oxidase O 2 dependence curve (the Michaelis‐Menten constant K m = 0.0108 kPa; critical O 2 pressure, 1–2 kPa), the declining rate of O 2 consumption proved to be biphasic: an initial, long semi‐linear part, reflecting the spread of severe hypoxia within the stele, followed by a short curvilinear fall, reflecting its extension through the pericycle and cortex. • We conclude that the initial respiratory decline in root respiration recently noted in respirometry studies is attributable to the spread of severe hypoxia from the root centre, rather than a conservation of O 2 by controlled down‐regulation of respiration based on O 2 sensors.