Plant senescence- or PCD-associated nucleases share significant homology with nucleases from different organisms.However,knowledge of their function is limited.Intracellular localization of the Arabidopsis senescenceand PCD-associated nuclease BFN1 was investigated.Analysis of BFN1-GFP localization in transiently transformed tobacco protoplasts revealed initial localization in filamentous structures spread throughout the cytoplasm,which then clustered around the nuclei as the protoplasts senesced.These filamentous structures were identified as being of ER origin.In BFN1GFP-transgenic Arabidopsis plants,similar localization of BFN1-GFP was observed in young leaves,that is,in filamentous structures that reorganized around the nuclei only in senescing cells.In late senescence,BFN1-GFP was localized with fragmented nuclei in membrane-wrapped vesicles.BFN1’s postulated function as a nucleic acid-degrading enzyme in senescence and PCD is supported by its localization patt.Our results suggest the existence of a dedicated compartment mediating nucleic acid degradation in senescence and PCD processes.