[C02] Developmental Biology

[C02-04] Morphogenesis of Sharp Tip in Leaf: an integrated experiment and simulation research

*Zining Wang¹, Atsushi Mochizuki², Yasuhiro Inoue², Hirokazu Tsukaya¹ (1. The University of Tokyo (Japan), 2. Kyoto University (Japan))

Keywords:

plant organ morphogenesis,Cell division,Cell expansion,sharp apex,vertex model,Triadica sebifera,plant development

Leaf shape is important for photosynthesis, and its tip region may hold the key to environmental adaptation. Prior experimental studies have mainly focused on the leaf tip function with limited understanding of its morphogenesis. To study this morphogenesis, we quantified leaf tips by curvature analysis, finding that tip regions were represented by exceptionally steep positive curvatures, with negative curvatures at the boundary between tips and bases. Such discontinuity in curvature indicated a spatial difference in tissue growth and cell behaviors. To date, leaf shape with such a heterogeneous system has not been studied. To tackle this, Triadica sebifera leaves were chosen as research materials, for their acute tips and impressive negative curvature connect tips and rounded bases. We examined the cell expansion and cell division in both tip and base part at different developmental stages. We first suspected an elongated cell expansion pattern like in roots, but surprisingly we did not observe it. Instead, we found a spatial pattern of biased cell division angles: cells in tip region divided in vertical direction and cells in basal part divided in random direction. We name it as biregional cell division angles, which has not been proposed in previous research. And with vertex model simulation, we proved that such biregional cell division angles were enough to generate sharp tips. Further simulations and experiments were conducted to assess the generality of this tip formation mechanism.