Changes in apoptosis-like programmed cell death and viability during the cryopreservation of pollen from Paeonia suffruticosa

Pollen after cryopreservation has a variety of change trends in viability, with most pollens showing decreased viability. The role of apoptosis-like programmed cell death (AL-PCD) in changing viability is not exactly clear. AL-PCD is an important biological activity of cells that plays a key role in the normal development of plants, maintenance of homeostasis and resistance to interference from various environmental factors. However, a relationship between the diverse changes in pollen viability after liquid nitrogen (LN) preservation and AL-PCD has rarely been reported. The results of this study show that after cryopreservation, the viability of pollen from six cultivars of Paeonia suffruticosa presents different changes, and the occurrence of AL-PCD in pollen of these six cultivars varies. When the viability of the cultivars was significantly higher than that of fresh pollen or the viability showed no significant difference from that of fresh pollen, intracellular reactive oxygen species (ROS) generation was not significantly changed and the activity of the caspase-3-like enzyme was relatively low. When the viability of the cultivars after cryopreservation was significantly lower than that of fresh pollen, ROS generation significantly increased and the caspase-3-like enzymatic activity was higher than the control level. The pollen apoptosis rate increased for all three viability change types, and correlation analysis results demonstrated a significant negative correlation between the apoptosis rate and pollen viability (P