PROMOTION OF PLANT GROWTH BY SOIL BACTERIA THAT REGULATE PLANT ETHYLENE LEVELS

摘要

One of the central the mechanisms used by many soil bacteria to directly promote plant growth is the production of the enzyme 1-aminocyclopropane-l-carboxylate (ACC) deaminase. This enzyme facilitates plant growth as a consequence of the fact that itsequesters and cleaves plant-produced ACC (the immediate precursor of ethylene in plants), thereby lowering the level of ethylene in the plant. In turn, decreased ethylene levels allow the plant to be more resistant to a wide variety of environmental stresses, all of which induce the plant to increase its endogenous level of ethylene; stress ethylene exacerbates the effects of various environmental stresses. Thus, ACC deaminase-containing soil bacteria decrease a significant portion of the physiologicaldamage to plants following environmental stresses including phytopathogen infection, exposure to extremes of temperature, high salt, flooding, drought, exposure to metals and organic contaminants, and insect predation. ACC deaminase-containing Rhizobiaspp. are also significantly more efficient at nodulating their legume hosts than are rhizobial strains that lack the activity of this enzyme. The results of a wide range of studies using several different plants and soil bacteria are discussed in the context of a previously proposed model for the functioning of ACC deaminase-containing bacteria. In addition, the plant genes that are expressed as a consequence of the interaction with ACC deaminase-containing soil bacteria, and some of the bacterial regulatory factors involved are also discussed.