Alternative Respiratory Pathway Component Genes (AOX and ND) in Rice and Barley and Their Response to Stress.

Plants have a non-energy conserving bypass of the classical mitochondrial cytochrome c pathway, known as the alternative respiratory pathway (AP). This involves type II NAD(P)H dehydrogenases (NDs) on both sides of the mitochondrial inner membrane, ubiquinone, and the alternative oxidase (AOX). The AP components have been widely characterised from Arabidopsis, but little is known for monocot species. We have identified all the genes encoding components of the AP in rice and barley and found the key genes which respond to oxidative stress conditions. In both species, AOX is encoded by four genes; in rice , , and representing four clades, and in barley, , , and , but no . All three subfamilies of plant genes, , and are present in both rice and barley, but there are fewer genes compared to Arabidopsis. Cyanide treatment of both species, along with salt treatment of rice and drought treatment of barley led to enhanced expression of various AP components; there was a high level of co-expression of and , along with during the stress treatments, reminiscent of the co-expression that has been well characterised in Arabidopsis for and .