PLANT PHYSIOLOGY , Vol 108, Issue 3 1179-1183, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Partitioning of Electrons between the Cytochrome and Alternative Pathways in Intact Roots
O. K. Atkin, R. Villar and H. Lambers
Department of Plant Ecology and Evolutionary Biology, Utrecht University, P.O. Box 800.84, 3508 TB Utrecht, The Netherlands
To test the hypothesis that the cytochrome pathway is not invariably
saturated when the alternative pathway is engaged, we titrated root
respiration of several species with KCN (an inhibitor of the cytochrome
pathway), both in the absence and presence of an inhibitor of the
alternative pathway (salicylhydroxamic acid, SHAM). The slopes of the
resultant KCN [rho] plots ([rho]cyt) were then used to determine whether
the cytochrome pathway was saturated in each species. The species used were
Festuca ovina ssp. ovina L., Phaseolus vulgaris L., and six Poa species
(Poa pratensis L., Poa compressa L., Poa trivialis L., Poa alpina L., Poa
costiniana Vick., and Poa fawcettiae Vick.). Although the cytochrome
pathway was saturated in a number of species (i.e. [rho]cyt values were
1.0), several others exhibited [rho]cyt values of less than 0.5.
Alternative pathway capacity correlated negatively with [rho]cyt, with
[rho]cyt values of less than 1.0 occurring in tissues in which the
alternative pathway capacity was greater than 25 to 30% of total
respiration. The species that did not show full engagement of the
cytochrome pathway rarely exhibited SHAM inhibition in the absence of KCN.
We conclude that this lack of SHAM inhibition is not due to a lack of
alternative pathway engagement but rather to the diversion of electrons
from the alternative pathway to the unsaturated cytochrome path following
the addition of SHAM.
