Analysis of Type II NAD(P)H Dehydrogenases.

Plant mitochondria contain at least four type II NAD(P)H dehydrogenases that link NAD(P)H oxidation to the inner membrane electron transport chain and bypass proton pumping at Complex I, hence ATP synthesis. These activities have been found in mitochondria isolated from all plant species analyzed to date. In this chapter, methods are presented to analyze the expression of genes encoding these dehydrogenases and to detect protein levels in mitochondria isolated from Arabidopsis (Arabidopsis thaliana).

Alterations in the mitochondrial alternative NAD(P)H Dehydrogenase NDB4 lead to changes in mitochondrial electron transport chain composition, plant growth and response to oxidative stress.

The branched respiratory electron transport chain of plants contains a non-phosphorylating alternative pathway consisting of type II NAD(P)H dehydrogenases on both sides of the inner membrane linked through the ubiquinone pool to an alternative oxidase (AOX). T-DNA and RNA interference (RNAi) were used to reduce gene expression to characterize the external NAD(P)H dehydrogenase NDB4 in Arabidopsis. The ndb4 lines showed different levels of suppression of NDB4 protein, leading to increases in NBD2 and AOX1a mRNA and protein levels in all lines.

Manipulation of alternative oxidase can influence salt tolerance in Arabidopsis thaliana.

The growth and development of plants can be limited by environmental stresses such as salinity. It has been suggested that the non-phosphorylating alternative respiratory pathway in plants, mediated by the NAD(P)H dehydrogenase [NAD(P)H DH] and alternative oxidase (AOX), is important during environmental stresses. The involvement of this alternative pathway in a stress response may be linked to its capacity to uncouple carbon metabolism from adenylate control and/or the minimization of the formation of destructive reactive oxygen species (ROS).