Partitioning of Electrons between the Cytochrome and Alternative Pathways in Intact Roots

Abstract

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 p plots (pcyt) 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 cosfiniana Vick., and Poa fawcettiae Vick.). Although the cytochrome pathway was saturated in a number of species (i.e. pcyt values were 1 A), several others exhibited pcvt values of less than 0.5. Alternative pathway capacity correlated negatively with pcyt, with pCyt values of less than 1 .O occurring in tissues in which the alternative pathway capacity was greater than 25 to 30% of total respiration. l h e 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.

2,6-Dichloro-phenol Indophenol Prevents Switch-over of Electrons between the Cyanide-Sensitive and -Insensitive Pathway of the Mitochondrial Electron Transport Chain in the Presence of Inhibitors

“…1). It has been shown that e Ϫ can be diverted to either of the pathways when one of the pathways is saturated or restricted (10,11,22), and it leads to a higher rate of oxygen uptake than what should have been in the absence of inhibitors. Apparent inhibition by DCPIP in the presence of CN or SHAM suggested that e Ϫ , rather than being diverted to another oxidase (AO or cytochrome oxidase), are being captured by DCPIP.…”

“…This would mean that under uninhibited conditions e Ϫ are being partitioned between the cyt pathway and APR and none of the pathways is fully saturated (22). Addition of CN would restrict the cyt pathway leading to increased reduction poise of the Q pool (12).…”

Respiration of turions and winter apices in aquatic carnivorous plants

“…RD was measured in the turions after a 3-h exposure (20±1 • C, darkness, thoroughly shaken) to either 0.5 mM KCN, or 5 mM salicylhydroxamic acid (SHAM), or 0.5 mM KCN + 5 mM SHAM. The latter mixed solution is known to inhibit cyanide-resistant respiration (e.g., Kapulnik et al 1992;Atkin et al 1995;Millar et al 1998). The inhibitors were added to the basic diluted mineral nutrient solution.…”

Ecophysiological characterization of carnivorous plant roots: Oxygen fluxes, respiration, and water exudation

“…s -1 , Loveys et al 2003), or 8 meadow species (2.5 -3.4 µmol kg -1 (f.m.) s -1 , Atkin et al 1995). Relatively high RRs in Drosera rotundifolia and Dionaea muscipula correspond to high rates of water exudation in these species (cf.…”