Ethylene and plant responses to stress

When plants are subject to a variety of stresses they often exhibit symptoms of exposure to ethylene. Although this relationship usually results from induction of ACC synthase thus raising the concentration of the precursor of ethylene, it is now apparent that there are numerous other ways that stresses produce ethylene-like symptoms. This complex relationship between stress and ethylene-like symptoms is here termed the stress ethylene syndrome. ACC synthase exists as a multi-gene family whose individual members are differentially regulated, many by various stresses. In addition, ACC oxidase. AdoMet synthetase, enzymes in the Yang methionine cycle, and enzymes that conjugate ACC are regulated by stress. In more unusual cases, ethylene production is not increased by stress or may be reduced. There is evidence for stress effects on perception of ethylene and the potential exists that some steps of the ethylene signal transduction pathway may be influenced by stress. Because of the variability possible in the stress ethylene syndrome, it continues to be studied for a number of stresses and species. In particular, attention is being given to wounding, mechanical stress, drought, heat and water deficit stress, chilling, air pollution, chemical and salt stress, and low O₂stress. It is becoming more apparent that a number of stress responses involve interactions with other hormones.