Biregional division angles generate sharp apex and concave joints in leaves

Leaf apex, the distal end of the leaf blade, exhibits enormous shape variations across plant species. Among these variations, the sharp apex, characterized by its pointed tip, is important in species identification and environmental adaptation. Despite its taxonomic and ecological importance, the developmental mechanisms underlying the formation of a sharp apex remain unknown. The present study aims to investigate the curvature patterns and morphogenesis of the sharp apex to uncover these mechanisms using Triadica sebifera leaves. Our research revealed that the sharp apex marks the maximum positive curvature, and is flanked by concave joints with negative curvatures, suggestive of differential tissue growth and spatially regulated cellular behavior. Through a combination of wet experiments and numerical simulations, we demonstrated that biregional cell division angles, rather than locally differing cell expansion or division frequency, play a determining role in shaping distinct leaf morphology. Our study highlights the importance of spatiotemporal regulation of cell division angles during leaf development, suggesting that a biregional growth pattern and cellular behavior contribute to diversity in leaf apex morphology.