Increased Respiratory Restriction during Phosphate-Limited Growth in Transgenic Tobacco Cells Lacking Alternative Oxidase

Abstract

We found that mitochondrial alternative oxidase (AOX) protein and the capacity for CN-resistant respiration are dramatically increased in wild-type tobacco (Nicotiana tabacum) suspensioncultured cells in response to growth under P limitation, and antisense (AS8) tobacco cells unable to induce AOX under these conditions have altered growth and metabolism. Specifically, we found that the respiration of AS8 cells was restricted during P-limited growth, when the potential for severe adenylate control of respiration (at the level of C supply to the mitochondrion and/or at the level of oxidative phosphorylation) is high due to the low cellular levels of ADP and/or inorganic P. As a result of this respiratory restriction, AS8 cells had altered growth, morphology, cellular composition, and patterns of respiratory C flow to amino acid synthesis compared with wild-type cells with abundant AOX protein. Also, AS8 cells under P limitation displayed high in vivo rates of generation of active oxygen species compared with wild-type cells. This difference could be abolished by an uncoupler of mitochondrial oxidative phosphorylation. Our results suggest that induction of non-phosphorylating AOX respiration (like induction of adenylate and inorganic P-independent pathways in glycolysis) is an important plant metabolic adaptation to P limitation. By preventing severe respiratory restriction, AOX acts to prevent both redirections in C metabolism and the excessive generation of harmful active oxygen species in the mitochondrion.

Extending Cassava Root Shelf Life via Reduction of Reactive Oxygen Species Production

“…The wild-type rates are within the range of previous cyanide-insensitive respiratory rates for cassava tuberous roots published by Passam (1976), ranging from 15 to 57 nmol oxygen mg 21 protein min 21 . Significantly, wild-type cassava has substantially lower AOX rates compared with other crops such as soybean (Glycine max; 66 nmol mg 21 protein min 21 ; Kearns et al, 1992) and tobacco (Nicotiana tabacum) under nutrient stress (60 nmol mg 21 protein min 21 ; Parsons et al, 1999). This may be due to the fact that the cassava storage root is metabolically less active compared with other plant roots.…”

Differential Expression of Alternative Oxidase Genes in Maize Mitochondrial Mutants

“…The high level of AOX apparently prevents oxidative stress in the NCS plants during their life cycle. Conversely, tobacco cell cultures with antisense suppression of AOX (AS8) were found to have excessive ROS levels in mitochondria (Maxwell et al, 1999), as well as altered growth under phosphate limitation (Parsons et al, 1999;Yip and Vanlerberghe, 2001). Thus, AOX appears to be vital for the survival and development of plant cells with high levels of mutant mitochondria.…”

Mitochondrial Reactive Oxygen Species. Contribution to Oxidative Stress and Interorganellar Signaling

“…Therefore, NO production could lead to increased mtROS formation. Many stresses cause oxidative damage in plant tissues, and increases in mtROS resulting from mtETC perturbations have been implicated as at least partly responsible for the damage and plant responses observed in several of these cases, including chilling (Prasad et al, 1994a(Prasad et al, , 1994bPurvis et al, 1995), salt stress (Hernández et al, 1993;Mittova et al, 2003), and phosphate deficiency (Juszczuk et al, 2001;Parsons et al, 1999;Malusà et al, 2002).…”