Comparative analysis to investigate a possible mechanism for cell enlargement in succulent leaves of Crassothonna capensis (Asteraceae)

Succulent plants, characterized by the presence of water-storage tissues, often exhibit distinctive leaf morphology. However, their developmental mechanisms remain largely unknown, partly due to the lack of an appropriate model plant. In this study, we evaluated the potential of Asteraceae species as a model system for investigating the mechanisms underlying leaf succulence. First, we analyzed the leaf anatomical and cellular characteristics of succulent plants in the genera Caputia, Crassothonna, Curio, Othonna, and Senecio. To explore a potential mechanism involved in succulent leaf development, we focused on endoreduplication-genome replication without mitosis-and measured the ploidy levels of leaf cells in each species using flow cytometry (FCM) to assess the relationship between leaf succulence and endoreduplication. The FCM data indicated that succulent leaves of Caputia, Curio, Senecio, and Othonna were not associated with endoreduplication. In contrast, endoreduplication was detected in enlarged leaf cells of Crassothonna capensis, while no endoreduplication was observed in the peduncles, which did not appear succulent, or in ligules, which are the lateral organs homologous to leaves. These results suggest that unknown mechanisms other than endoreduplication contribute to leaf succulence in certain genera, and that endoreduplication is regulated in an organ-specific manner in Cr. capensis. Additionally, even if endoreduplication is involved in leaf succulence, it may serve as a supplementary mechanism for cell enlargement. Collectively, these findings highlight Crassothonna and its related genera in Asteraceae as a promising group for studying the mechanisms of leaf succulence.