CEL I enzyme from celery, as a member of S1 family of nucleases, is known for its high specific activity in recognition and cleavage of base-substitution mismatches on heteroduplex DNA molecules. Despite valuable applications of the enzyme in mutation screening studies, little is known about its function at cellular level. In the present study, we investigated the pattern of CEL I expression in ethyl methanesulfonate (EMS) treated celery plants. An abnormal growth pattern along with wide and clear lesions were observed on the treated plants. A considerable increase in the level of CEL I protein happened in vegetative and generative parts of EMS-treated plants compared with controls. Despite such induction, the enzyme is not expected to be involved in DNA repair during EMS treatment due to the absence of any known nuclear localization signal in the deduced sequence of CEL I protein. Considering the fact that CEL I orthologs are induced during programmed cell death, the high expression of CEL I upon EMS treatment could be due to the stress and necrotic cell death created by the treatment

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