Reactive Oxygen Species Homeostasis Regulates Pistil Development and Pollination in Salix linearistipularis

During the development of the gametophyte in angiosperms, a series of processes occurs, including pollination, pollen recognition, adhesion, hydration, germination, pollen tube growth, and the guidance of the pollen tube toward the ovule for the delivery of sperm cells to the female gametophyte. These processes require a substantial energy supply, which is provided by cellular respiration in the plant. Throughout this sequence, the generation of reactive oxygen species (ROS) is concomitantly observed. At present, the mechanisms underlying ROS production remain incompletely understood, especially in plant trees such as Salix linearistipularis. In this study, pistils of S. linearistipularis were used as experimental materials, and pistils were divided according to their development into three stages-S1, S2, and S3. Transcriptome sequencing (RNA-Seq) was performed for the three developmental stages, and the results indicated that metabolic pathways associated with oxidoreductase activity were highly significant during pistil development in S. linearistipularis. During pistil development, the levels of ROS accumulated rapidly. After pollination, with the adhesion and germination of pollen, the levels of ROS decreased significantly. Moreover, bidirectional regulation of ROS levels revealed that treatment with ROS inducers and scavengers led to increased and decreased ROS accumulation, which were accompanied by the inhibition and promotion of pollen tube number and length. These two opposite results indicate that ROS are the key factor regulating pistil development and pollen tube germination in S. linearistipularis.