Precocious programmed cell death and tapetal dysfunction cause pollen abortion in Lycium barbarum male-sterile line ningqi-5.

Male sterility is a valuable trait in plant breeding that enables efficient hybrid seed production by eliminating the need for manual emasculation. In Lycium barbarum, the male sterile line Ningqi-5 exhibits complete pollen abortion, but the underlying cytological mechanisms remain unclear. In this study, we systematically compared anther development between the fertile line Ningqi-1 and the male sterile line Ningqi-5 using light microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and TUNEL assays to elucidate the cellular basis of male sterility. Our results revealed that microspore abortion in Ningqi-5 occurs at the tetrad stage, characterized by delayed callose wall degradation, failure of microspore release, and progressive degeneration of tetrads. TEM and SEM analyses showed abnormal tapetal ultrastructure in Ningqi-5, including thickened cell walls, absence of Ubisch bodies, aggregated and adherent secretions, and disrupted sporopollenin transport. Furthermore, TUNEL assays demonstrated premature initiation of programmed cell death (PCD) in the tapetum of Ningqi-5 during the tetrad stage. These defects collectively disrupt nutrient supply, exine formation, and microspore maturation. We conclude that male sterility in L. barbarum Ningqi-5 results from a synergistic interplay of three key factors, include failure to degrade the callose wall, impaired tapetal secretion function, and precocious tapetal PCD. This study provides a comprehensive cytological framework for understanding pollen abortion in L. barbarum.