Regulation of aldehyde oxidase and nitrate reductase in roots of barley (Hordeum vulgare L.) by nitrogen source and salinity

Abstract

The barley (Hordeum vulgare) mutant Az34 which exhibited a low basal level of ABA also had a reduced capacity The molybdenum cofactor (MoCo) is a component of to produce abscisic acid during water stress ( Walkeraldehyde oxidase (AO EC 1.2.3.1), xanthine dehydro- Simmons et al., 1989). The mutation is located in one of genase (XDH EC 1.2.1.37) and nitrate reductase (NR, the genes controlling the expression of MoCo (Mendel, EC 1.6.6.1). The activity of AO, which catalyses the 1997), a constitutive component of Mo-enzymes such as last step of the synthesis of abscisic acid (ABA), was NR, XDH and AO. This mutant was found to lack studied in leaves and roots of barley (Hordeum vulgare aldehyde oxidase activity in the presence of several subL.) plants grown on nitrate or ammonia with or without strates such as abscisic aldehyde and heptaldehyde. salinity. The activity of AO in roots was enhanced in Wilting mutants of tomato (Lycopersicon esculentum), plants grown with ammonium while nitrate-grown sitiens and flacca, which do not produce ABA have been plants exhibited only traces. Root AO in barley was shown to lack the capacity to oxidize abscisic aldehyde enhanced by salinity in the presence of nitrate or ( Taylor et al., 1988; Sindhu et al., 1990). Recently it has ammonia in the nutrient medium while leaf AO was been found that the flc mutant of tomato lacks aldehyde not significantly affected by the nitrogen source or oxidase and xanthine dehydrogenase but not nitrate salinity of the medium.