The Use of ACC Deaminase-Containing Plant Growth-Promoting Bacteria to Protect Plants Against the Deleterious Effects of Ethylene

Abstract

Plant growth-promoting bacteria can affect plant growth and development in two different ways: indirectly or directly (Glick 1995; Glick et al. 1999). Indirect promotion of plant growth occurs when these bacteria decrease or prevent some of the deleterious effects of a phytopathogenic organism by any one or more of several different mechanisms. In general, bacteria can directly promote plant growth by providing the plant with a compound that is synthesized by the bacterium or facilitating the uptake of nutrients. There are several ways in which plant growth-promoting bacteria can directly facilitate the proliferation of their plant hosts. They may fix atmospheric nitrogen; produce siderophores which can solubilize and sequester iron and provide it to plants; synthesize phytohormones, including auxins, cytokinins, and gibberellins which can enhance various stages of plant growth; solubilize minerals such as phosphorus; and synthesize enzymes that can modulate plant growth and development (Brown 1974; Kloepper et al. 1986, 1989; Davison 1988; Lambert and Joos 1989; Patten and Glick 1996; Glick et al. 1999). A particular bacterium may affect plant growth and development using any one, or more, of these mechanisms. Moreover, many plant growthpromoting bacteria possess several properties that enable them to facilitate plant growth and, of these, may utilize different ones at various times during the life cycle of the plant. The mechanism most often invoked to explain the various effects of plant growth-promoting bacteria on plants is the production of phytohormones, most notably auxin (Brown 1974; Tien et al. 1979; Patten and Glick 1996). Since plants as well as plant growth-promoting bacteria can synthesize auxin, it is important when assessing the consequences of treating a plant with a plant growth-promoting bacterium, to distinguish between the bacterial stimulation of plant auxin synthesis and bacterial auxin synthesis (Gaudin et al. 1994). To complicate matters, the response of plants to auxin-producing