Autophagy is associated with male sterility in pistillate flowers of Maytenus obtusifolia (Celastraceae)

Programmed cell death (PCD) is defined as a sequence of genetically regulated events leading to controlled and organised cellular degradation. It plays a vital role in plant development; however, little is known about the role of PCD in reproductive development. Sterility in pistillate flowers of Maytenus obtusifolia Mart. has been shown to be related to cytoplasmic male sterility (CMS) based on reproductive biology and anatomical analysis. The recurrent PCD led us to investigate changes in the tapetum and sporogenic tissue during the establishment of male sterility using light and transmission electron microscopy combined with the use of TUNEL (terminal deoxynucleotidyl transferase mediated dUDP end-labelling) assay. The interruption of pollen development in pistillate flowers is a result of premature PCD in the tapetum and consequently in the sporogenic cells. Autophagy, via macroautophagy, occurs in the sporogenic cells and involves the formation of autophagosomes, through rough endoplasmic reticulum, and of complex macroautophagic structures. In the final stage of PCD, massive autophagy takes place. Male sterility in female individuals is thus reasonably interpreted as sporophytic CMS associated to autophagy.