Programmed cell death during rice leaf senescence is nonapoptotic.

•  The cellular events associated with programmed cell death during leaf senescence in rice (Oryza sativa) plants are reported here. •  The cytological sequence of senescence-related changes in rice leaves was studied by transmission electron microscopy, in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling (TUNEL) assay and DNA ladder assay. •  Cell death in senescing mesophyll cells was marked by depletion of cytoplasm in a tightly controlled manner. However, no apparent morphological feature associated with apoptosis was observed. Nuclear DNA fragmentation was detectable as early as during leaf unfolding and the subsequent developmental and senescent stages. The occurrence of DNA fragmentation correlated well with the size-shift of chromosomal DNA on agarose gel after electrophoresis. However, DNA fragmentation was not accompanied by generation of oligonucleosomal DNA fragments. •  These features of cell death occurring during leaf senescence in monocot rice are quite different from features characteristic of apoptosis in animals. The implications of these results for cellular events associated with rice leaf senescence are discussed.