Induced Tetraploid <i>Lilium leichtlinii</i> Sustains Generative Cell Division in Pollen Tubes under Heat Stress

Double fertilization is essential for sexual reproduction in flowering plants. However, with ongoing global climate change, the increasing frequency of abiotic stresses such as extreme heat and cold has posed significant challenges to plant reproductive development. Temperature fluctuations significantly impact key stages of male gametophyte development, including pollen germination, pollen tube growth, and generative cell division. Disruptions to these processes can lead to reduced fertilization efficiency, thereby impairing fertility and crop yield. Although polyploid plants generally exhibit enhanced tolerance to abiotic stress, the mechanisms by which pollen from polyploid plants regulate reproductive cell division under temperature stress remain poorly understood. In this study, we investigated the dynamics of pollen tube development and generative cell division in diploid and tetraploid Lilium leichtlinii ‘Hakugin’ under various temperature treatments including 12°C, 17°C, 22°C, 27°C, 32°C, and 37°C. Flow cytometry was employed to monitor changes in nuclear DNA content during pollen tube elongation, allowing assessment of generative cell division. The results revealed that high-temperature exposure at 37°C markedly suppressed the generative cell division process in diploids, suggesting possible heat-induced cell cycle arrest. In contrast, after 24 h of incubation at 37°C, the completion rate of generative cell division in pollen tubes from tetraploid plants was consistently higher than that in their diploid counterparts. These findings demonstrate that polyploid plants have advantages in cell cycle regulation under heat stress. This trait may help them better cope with heat conditions during reproductive development. Our results provide new insights into the robust reproductive development of polyploid plants under heat stress.