Effects of KCN and Salicylhydroxamic Acid on the Root Respiration of Pea Seedlings

Abstract

Polarography, using cylindrical platinum electrodes, proved suitable for measuring changes in the internal apical 02 concentration of the primary root of pea (Pisum sativum L. cv Meteor) effected by KCN and/or salicylhydroxamic acid (SHAM) in the bathing medium. An electrical rootaeration analog was used to help evaluate some of the results. Concentrations of KCN -0.05 millimolar had no significant effect. In response to 0.1 millimolar KCN, the 02 concentration rose substantially for approximately 2 hours, then declined, and after 10 hours had frequently fallen below the pretreatment level. Such changes suggest an initial inhibition of cytochrome oxidase-mediated 02 uptake followed by an induction of the alternative, cyanide-resistant respiratory pathway. These treatments proved nonlethal. Changes in 02 concentration similar to those described for 0.1 millimolar KCN were observed in response to 1 and 10 millimolar KCN but these treatments were lethal and the root apex became soft and often appeared flooded. Roots survived and showed no signifiant responses when treated with SHAM at concentrations -5 millimolar. However, when the alternative pathway had been (apparently) induced by 0.1 millimolar KCN, the addition of 5 mIllimolar SHAM to the bathing medium caused a substantial and persistent rise in the root apical 02 concentration, suggesting that this (nonlethal) concentration of SHAM could indeed inhibit 02 uptake via the cyanide-resistant pathway.It is concluded that while 02 uptake normally occurs by the cytochrome pathway in the primary pea root, the alternative, cyanide-resistant pathway can be induced by 0.1 millimolar KCN.Cyanide is a known inhibitor of Cyt oxidase yet the capacity to respire in its presence appears to be widespread throughout the plant kingdom (3, 5). There is now general agreement that cyanide-insensitive respiration is the result of an electron flow which bypasses the classical, Cyt pathway at the position of ubiquinone (20,21), 02 being ultimately reduced by an 'alternative' oxidase. Although the nature of the alternative oxidase has yet to be identified, it is known that electron flow to this terminal oxidase is insensitive to cyanide but sensitive to the hydroxamic acid group of compounds, e.g. SHAM2 (16).Despite the apparently widespread distribution of cyanide-insensitive respiration, its physiological significance remains uncertain. Several areas in which such respiration might be of importance have been reviewed by Lambers (7) and these include roles in heat production, fruit ripening, respiration ofplants that contain high levels ofcyanogenic glycosides producing HCN upon wounding, oxidation of NADH, and ion transport and osmoregulation.'To whom reprint requests should be sent. ' Abbreviations and trivial name: SHAM, salicylhydroxamic acid; ROL, radial oxygen loss; disulfiram, tetraethylthiuram disulfide.Also, Lambers suggests that cyanide-insensitive respiration might play an important role (at least in roots) in the oxidation of sugars that have been translocated to...

Coordinate Regulation of Cytochrome and Alternative Pathway Respiration in Tobacco

“…The concepts of growth and maintenance respiration are discussed elsewhere (1,13). Pea roots were also shown to remain viable but not to elongate after induction of AP respiration in response to inhibition of the CP by KCN (28). These observations and ours suggest that the AP may provide the maintenance respiration required for cells to survive during periods when the CP is suppressed.…”

“…For example, treatment of rice roots with low concentrations of KCN or NaN3 for 6 h resulted in increased CN-resistant respiration, although it was not shown whether this CN-resistant respiration was sensitive to SHAM (11). In pea roots, a CN-resistant and SHAM-sensitive component of respiration was induced after several hours of KCN treatment (28). From the above reports, it is not clear whether the KCN treatment increased the capacity or simply the engagement of the AP.…”

Variations in the Alternative Oxidase in Chlamydomonas Grown in Air or High CO2

“…In such cases measurements of V,,, were probably underestimated and the capacity of the alternative pathway (JV81t) may be overestimated. There are also reports that addition of 1 mm cyanide increased the rate of 02 uptake in Chlorella protothecoides (10) (16), by low concentrations of KCN in the roots of pea seedlings (23), and by sodium azide in soybean leaves (18). We observed that either salicylic acid or a low concentration of KCN also induced the alternative respiratory capacity in high C02-grown Chlamydomonas cultures, at the time when normally the alternative respiration capacity was low during the log phase of growth (Table II).…”

Regulation of respiration in rotenone-treated tobacco cell suspension cultures

“…Inhibition of the cytochrome pathway induces a large increase in the expression of the alternative pathway in higher plants (Kano and Kumazawa 1972;Webb and Armstrong 1983), yeast (Minagawa and Yoshimoto 1987) and tobacco cell cultures (Vanlerberghe and McIntosh 1992). Inhibition of mitochondrial protein synthesis by CAP also increases both the activity and protein level of alternative oxidase in wheat shoots, pea leaves (Zhang et al 1996), potato tuber callus (van der Plas et al 1981;van der Plas and Wagner 1983), Neurospora crassa (Edwards and Rosenberg 1976;Friedrich et al 1989), and in cell suspensions of Petunia hybrida (van Emmerik et al 1993).…”