The occurrence and control of nitric oxide generation by the plant mitochondrial electron transport chain

Abstract

The plant mitochondrial electron transport chain (ETC) is bifurcated such that electrons from ubiquinol are passed to oxygen via the usual cytochrome path or through alternative oxidase (AOX). We previously showed that knockdown of AOX in transgenic tobacco increased leaf concentrations of nitric oxide (NO), implying that an activity capable of generating NO had been effected. Here, we identify the potential source of this NO. Treatment of leaves with antimycin A (AA, Q -site inhibitor of Complex III) increased NO amount more than treatment with myxothiazol (Myxo, Q -site inhibitor) despite both being equally effective at inhibiting respiration. Comparison of nitrate-grown wild-type with AOX knockdown and overexpression plants showed a negative correlation between AOX amount and NO amount following AA. Further, Myxo fully negated the ability of AA to increase NO amount. With ammonium-grown plants, neither AA nor Myxo strongly increased NO amount in any plant line. When these leaves were supplied with nitrite alongside the AA or Myxo, then the inhibitor effects across lines mirrored that of nitrate-grown plants. Hence the ETC, likely the Q-cycle of Complex III generates NO from nitrite, and AOX reduces this activity by acting as a non-energy-conserving electron sink upstream of Complex III.

Signaling interactions between mitochondria and chloroplasts in Nicotiana tabacum leaf

“…). Conversely, KD of AOX, which further reduces electron flow to oxygen when Complex III is inhibited (Alber et al ), enhanced the induction of these genes by AA, relative to WT (Fig. ).…”

“…The MDGs identified by Maxwell et al () appear to respond in a relatively specific manner in tobacco leaf to the capacity for respiratory electron flow to oxygen. First, OE of AOX, which acts to maintain electron flow to oxygen when Complex III is inhibited (Alber et al ), largely blocked the induction of these genes by AA, relative to WT (Fig. ).…”

“…OLIGO inhibits the mitochondrial ATP synthase, rather than directly inhibiting respiratory electron transport. While OLIGO only slightly reduces oxygen consumption in tobacco leaf (Alber et al ), it did intensively increase the transcript abundance of each of the MDGs. Unlike AA and MYXO, OLIGO treatment caused a considerably more pronounced induction of all the MDGs following 3 h in the dark than in the light.…”

Mitochondrial Energy Signaling and Its Role in the Low-Oxygen Stress Response of Plants

“…NO production by the plant mtETC is elevated under hypoxia (reviewed by Hebelstrup and Møller, 2015). Alber et al (2017) recently proposed that NO generation happens at complex III, while AOX dampens NO generation rate. Gibbs et al (2014) further showed that NO acts in the stabilization of RAP2.12, and this requires cytosolic nitrate reductase activity in vivo.…”

Nitrogen Depletion Blocks Growth Stimulation Driven by the Expression of Nitric Oxide Synthase in Tobacco

“…Mitochondria are tightly linked to N metabolism and assimilation in plants (Szal and Podgórska, 2012) and is also a source of NO generated from nitrite and cytochrome c oxidoreductase activity in complex III (Alber et al, 2017). Additionally, NO was shown to be able to partially inhibit mitochondrial respiration (Gupta et al, 2018).…”