IntroductionCertain rhizosphere pseudomonads contain the enzyme 1-aminocyclopropane-1-carboxylate deaminase (ACCd; EC 4.1.99.4)(Ali et al. 2014; Belimov et al. 2007; Glick et al. 1994; Kamala-Kannan et al. 2010). This cytoplasmic enzyme hydrolyzes plant ACCthat includes cyclopropane ring to ammonia and – ketobutyrate(Honma and Shimomura 1978). In turn, ACC is the immediateprecursor of the plant hormone ethylene, an important mediatorof stress responses and plant growth and development (Morganand Drew 1997). The substrate for this enzyme is usually exudedby roots or seeds, actively taken up by bacteria, and then cleavedby their deaminase (Penrose and Glick 2001). These microor-ganisms utilize the ammonia, liberated from ACC, as a source ofnitrogen. Moreover, microbial uptake of rhizospheric ACC stimu-lates its secretion by plant tissues and thereby reduces ethylene