Soil flooding increased 1 -aminocyclopropane-1 -carboxylic (ACC) acid oxidase activity in petioles of wild-type tomato (Lycopersicon esculentum 1.) plants within 6 to 12 h in association with faster rates of ethylene production. Petioles of flooded plants transformed with an antisense construct to one isoform of an ACC oxidase gene (ACO1) produced less ethylene and had lower ACC oxidase activity than those of the wild type. Flooding promoted epinastic curvature but did so less strongly in plants transformed with the antisense construct than in the wild type. Exogenous ethylene, supplied to well-drained plants, also promoted epinastic curvature, but transformed and wild-type plants responded similarly. Flooding increased the specific delivery (flux) of ACC to the shoots (picomoles per second per square meter of leaf) in xylem sap flowing from the roots. The amounts were similar in both transformed and wild-type plants. These observations demonstrate that changes in ACC oxidase activity in shoot tissue resulting from either soil flooding or introducing ACC oxidase antisense constructs can influence rates of ethylene production to a physiologically significant extent. They also implicate systemic root to shoot signals in regulating the activity of ACC oxidase in the shoot.In this paper we examine the possible role of ACC oxidation in regulating ethylene biosynthesis in vegetative shoots of flooded tomato (Lycopersicon esculentum) plants.We also assess whether changes in ethylene production attributable to different levels of ACC oxidase activity are of physiological significance for the shoots of flooded plants. During soil flooding, the root environment becomes depleted of oxygen (Grable, 1966). In response, shoot systems show a wide range of physiological and biochemical changes. Some of these changes, such as petiole epinasty in tomato, may be adaptive (Armstrong et al., 1994). Epinasty can be observed within 6 to 12 h of flooding (Jackson and Campbell, 1975) and is brought about by the action of ethylene, following enhanced accumulation (Kawase, 1972) and production (Bradford and Dilley, 1978;

No abstract

No abstract

No abstract