Successful sexual reproduction of flowering plants requires precise inter-cellular communications between male and female cells. Pollen germination, pollen tube guidance and reception, and double fertilization are achieved by molecular dialogues among male and female cells, which are species-preferential and potentially induce speciation. However, these reproductive processes occur deep within the pistil tissue. Dynamics of cellular behaviors and molecular interactions remains elusive. It is also unknown whether reproductive barriers in these molecular interactions drive actual speciation. We have been taking approaches of live-cell analysis mainly using two models, Torenia and Arabidopsis. For example, two-photon deep-imaging analysis in Arabidopsis suggested sporophytic and gametophytic directional ques and rapid polytubey blocking in in vivo ovular guidance (Mizuta et al., EMBO Rep., in press). Bioassays lead to identification of non-proteinous molecules involved in competency controls of pollen tubes (e.g., Matsuura-Tokita et al., in submission; Mizukami et al., bioRxiv, 2024), which are rather general compared to species-preferential ovular guidance cues including LURE-type attractant peptides. We are now developing Torenia species models to study signaling molecules and reproductive barriers in various combinations including populations in the field. In this talk, our recent results in Torenia and Arabidopsis will be introduced to discuss the molecular mechanisms of sexual reproduction, as well as reproductive barriers potentially driving speciation.