Regulatory Function of Ethylene in Plant Responses to Drought, Cold, and Salt Stresses

Unlike animals, plants cannot move, so they are forced to adapt to a changing environment. Abiotic stresses such as drought, cold, and salinity affect plant growth and development. Plants have evolved complex protective mechanisms to prevent the damage initiated by harsh stressors. Plant-emitted ethylene has been shown to be involved in plant responses to various stresses, acting as a signal molecule at low concentrations, and, in cooperation with other signaling compounds conferring protection against various stresses. As the simplest unsaturated hydrocarbon, ethylene regulates many diverse processes throughout the plant's lifetime, ranging from seed germination, growth, formation of apical hook, to organ senescence, fruit ripening, abscission, and stress responses. As a gaseous hormone, ethylene is produced in most plant tissues and cell types, freely diffusing in air and from cell to cell across membranes, and easily reaching target cells of either the same organ, organs other than those responsible for its biosynthesis, or even the target cells of neighboring plants. This chapter mainly focuses on the recent studies of ethylene-regulated plant responses to drought, salt, and low temperature stresses. Functional roles, importance, and molecular mechanisms underlying stress responses including ethylene biosynthesis, signaling, and transcriptional regulations will be analyzed. Studies on ethylene-regulated plant responses to environmental stresses have greatly advanced our understanding of plant stress tolerance and will potentially benefit us in engineering plants of economic importance.