Suppressed expression of the apoplastic ascorbate oxidase gene increases salt tolerance in tobacco and Arabidopsis plants

Abstract

Transgenic tobacco plants expressing the ascorbate oxidase (AAO) gene in sense and antisense orientations, and an Arabidopsis mutant in which the T-DNA was inserted into a putative AAO gene, were used to examine the potential roles of AAO for salt-stress tolerance in plants. AAO activities in the transgenic tobacco plants expressing the gene in sense and antisense orientations were, respectively, about 16-fold and 0.2-fold of those in the wild type. Under normal growth conditions, no significant differences in phenotypes were observed, except for a delay in flowering time in the antisense plants. However, at high salinity, the percentage germination, photosynthetic activity, and seed yields were higher in antisense plants, with progressively lower levels in the wild type and the sense plants. The redox state of apoplastic ascorbate in sense plants was very low even under normal growth conditions. Upon salt stress, the redox state of symplastic and apoplastic ascorbate decreased among the three types of plants, but was lowest in the sense plants. The hydrogen peroxide contents in the symplastic and apoplastic spaces were higher in sense plants, progressively lower in the wild type, followed by the antisense plants. The Arabidopsis T-DNA inserted mutant exhibited very low ascorbate oxidase activity, and its phenotype was similar to that of antisense tobacco plants. These results suggest that the suppressed expression of apoplastic AAO under salt-stress conditions leads to a relatively low level of hydrogen peroxide accumulation and a high redox state of symplastic and apoplastic ascorbate which, in turn, permits a higher seed yield.

Ascorbate oxidase: The unexpected involvement of a ‘wasteful enzyme’ in the symbioses with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi

“…Therefore, the function of an enzyme catalyzing the waste (oxidation) of ascorbate (AsA) to reduce oxygen to water is quite hard to explain. AO over-expressing plants are prone to ozone [3] and salt [4] stresses, whereas lower expression apparently confers resistance to unfavorable environmental conditions [4]. Therefore, AO activity appears at best not necessary, if not even dangerous, and the silencing of AO genes seems a valuable strategy to increase AsA content in crops [5].…”

Spermidine affects the transcriptome responses to high temperature stress in ripening tomato fruit

“…Numerous reports have shown that different pathways are interconnected and together regulate the plant response to biotic and abiotic stresses (Ludwig et al, 2005;Ma et al, 2006). Abscisic acid and ethylene play an important role in the complicated story of abiotic stress and, consequently, cross-talk between these two kinds of plant hormone has been reported (Yamamoto et al, 2005). The relationship between polyamine and ethylene was complex.…”

Cloning and Expression Analysis of an Ascorbate Oxidase (AO) Gene from Strawberry (Fragaria×ananassa cv. Toyonaka)

“…Thus it is concluded that AO plays important role in modulating and maintaining the redox state and ratio of AA pool (Pignocchi et al, 2006). Besides, it was found that depressed expression of AO gene promoted AA accumulation in tomato fruit (Yamamoto et al, 2005).…”