Effects of calcium ions and cell wall deposition on the pollen viability of Paeonia lactiflora after cryopreservation

Main conclusion

Four cultivars of Paeonia lactiflora pollen have a different viability after cryopreservation, and that the difference of pollen viability is related to calcium ions and cell wall deposition.

Abstract

Cryopreservation is a vital technique for preserving germplasm resources, offering extensive application prospects. Understanding the factors influencing pollen viability after cryopreservation is crucial for the permanent preservation and exchange of pollen resources. This study investigated pollen from four Paeonia lactiflora cultivars with varying viability after cryopreservation, aiming to determine whether calcium ions (Ca²⁺) and cell wall deposition affect these viability changes. The results showed that Ca²⁺-ATPase activity and cytoplasmic Ca²⁺ of all four cultivars exhibited an increasing trend after cryopreservation; the calmodulin (CaM) content varied with cultivars. Correlation analysis showed that fresh pollen viability was significantly negatively correlated with cytoplasmic Ca²⁺ content and positively correlated with Ca²⁺-ATPase activity, while pollen viability after cryopreservation exhibited a significantly negative correlation with cytoplasmic Ca²⁺ content and a positive correlation with CaM content. The pollen cell wall of the cultivar ‘Zi Feng Chao Yang’ (ZFCY), which showed increased viability after cryopreservation, contained significantly higher levels of low-temperature tolerance-related phospholipids and proteins compared to other cultivars. Additionally, all cultivars maintained a clear Ca²⁺ gradient at the tips of pollen tubes after cryopreservation, without significant callose accumulation. These findings suggest that differences in Ca²⁺ signaling and cell wall components deposition influence changes in pollen viability after cryopreservation, and the Ca²⁺ gradient and callose at the tip of pollen tubes are not responsible for preventing pollen tube growth.