Induction and activation of the alternative oxidase of potato tuber mitochondria

Abstract

1993. Induction and activation of the alternative oxidase of potato tuber mitochondria. -Physiol. Plant. 87: 134-141.Potato tubers (Sotanum tuberosum L. cv. Grata) were stored for at least 1 week at room temperature and then incubated with an equal amount of apples {Mains domestica L.) for 2 days. After this treatment, intact tuber mitochondria isolated by Percoll gradient centrifugation showed a high degree of induction of the alternative oxidase. measured as cyanide-resistant, salicylhydroxamic acid-sensitive respiration. With succinate as substrate an activity of more than 130 nmol O, (mg protein) ' min ' was obtained. An assay of the alternative oxidase using duroquinol as an electron donor was developed. To become reliable the assay required the presence of defatted bovine serum albumin (BSA) and catalase (EC I.II.1.6). Furthermore, a lowering of the assay temperature to 15°C improved the stability of the duroquinoi-based activity. One remarkable finding was that with duroquinol (or external NADH) as substrate the alternative oxidase was synergistically activated by succinate (as well as by malate) even in the presence of the succinate dehydrogenase inhibitor malonatc. Our interpretation is that succinate and maiate (indirectly) activate the alternative oxidase and that this activation is part of a physiological mechanism for regulation of the alternative oxidase.

Mitochondrial Electron Transport Regulation of Nuclear Gene Expression (Studies with the Alternative Oxidase Gene of Tobacco)

“…This is consistent with numerous studies on both isolated mitochondria and whole tissue that suggest that the AP is engaged in Oz consumption only when the CP becomes limiting or restricted (Theologis and Laties, 1978;Day and Lambers, 1983). It should be noted that partitioning between the two pathways may also be dependent on the substrates being oxidized by the mitochondria (Day et al, 1991;Wagner et al, 1992a), the level of potential allosteric activators of the AOX (Lidén and Akerlund, 1993;Millar et al, 1993), and possibly the oxidation state of an AOX sulfhydryl residue (Umbach and Siedow, 1993). More work is required to determine the significance of these regulatory mechanisms.…”

Specificity of the Organic Acid Activation of Alternative Oxidase in Plant Mitochondria

“…The very small concentrations of pyruvate needed to stimulate AOX (Fig. 1) and the high levels of ME in mitochondria from sweet potato (Table 11) and potato (Day et al, 1984) exacerbate this effect, especially when respiration is measured at acid pH, as was the case in the studies by Wagner et al (1989Wagner et al ( , 1995 and Lidén and Akerlund (1993). The latter authors recognized the need for succinate and malate to be metabolized to achieve their stimulating effect on AOX.…”

“…Succinate stimulated NADH oxidation even in the presence of the succinate dehydrogenase inhibitor malonate (Wagner et al, 1989;Lidén and Akerlund, 1993). Wagner et al (1989Wagner et al ( , 1995 showed that L-malate and its supposedly unmetabolized isomer, D-malate, stimulated AOX activity in potato callus mitochondria.…”

A role for active oxygen species as second messengers in the induction of alternative oxidase gene expression in Petunia hybrida cells

“…An increase of the 02 uptake via the alternative pathway can be caused either by extra protein synthesis or by activation (via organic acids [13][14][15][16] and/or thiol modifications in the enzyme [17,18]). However, after 1 h in the presence of 10 mM H202, CN-resistant respiration was not different from the control cells (data not shown), indicating that extra protein synthesis and not activation of already existing protein is involved in the increase in activity.…”

“…In this view, both the activation of the alternative pathway and induction of alternative oxidase gene expression contribute to the protection of the plant against active oxygen species. When substrate supply to the mitochondria is too high for the (impaired) cytochrome pathway, accumulating organic acids lower the K m of the oxidase for ubiquinol [13][14][15][16]18], and the increased activity of the pathway will prevent an increase of reduction levels of the respiratory components, which would lead to the formation of harmful active oxygen species. Whenever the (activated) capacity of the alternative oxidase is not sufficient and active oxygen species like H202 do accumulate, these products themselves induce the expression of extra alternative oxidase protein.…”