Autophagy and Apoptosis Associated with Abortive Pollen Development in the Cytoplasmic Male-sterile Line GP1BC1-12 of Platycodon grandiflorum

Platycodon grandiflorum (balloon flower) is widely cultivated for medicinal, edible, and ornamental purposes. The cytoplasmic male-sterile line GP1BC1-12 of P. grandiflorum has been used to produce hybrids, but its mechanism of sterility has not been studied. In this work, the mechanism was evaluated by a combination of transmission electron microscopy (TEM) and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling assay. Observations showed that autophagy and apoptosis were simultaneously present in the abortive anthers. Autophagy was indicated by the autophagic vesicles, abnormal arrangement of endoplasmic reticulum, and the vacuole’s invagination. Apoptosis was characterized by chromatin aggregation and DNA cleavage. It was concluded that programmed cell death is one of the direct reasons for cytoplasmic male sterility in P. grandiflorum . This study first noted the simultaneous presence of the features of apoptosis, microautophagy, and macroautophagy in the abortive anthers of P. grandiflorum.