Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan.
J Plant Res. 2024 Jan;137(1):143-155. doi: 10.1007/s10265-023-01503-2. Epub 2023 Oct 13.
Arrangement of plant leaves around the stem, termed phyllotaxis, exhibits beautiful and mysterious regularities and has been one of the most attractive subjects of biological pattern formation. After the long history of studies on phyllotaxis, it is now widely accepted that the inhibitory effect of existing leaf primordia on new primordium formation determines phyllotactic patterning. However, costoid phyllotaxis unique to Costaceae of Zingiberales, displaying spiromonostichy characterized by a steep spiral with a small divergence angle, seems to disagree with the inhibitory effect-based mechanism and has remained as a "genuine puzzle". We developed a new mathematical model, hypothesizing that each leaf primordium exerts not only the inhibitory effect but also some inductive effect. Computer simulations with the new model successfully generated a spiromonostichous pattern when these two effects met a certain relationship. The obtained spiromonostichy matched the real costoid phyllotaxis observed with Costus megalobractea, particularly for the decrease of the divergence angle associated with the enlargement of the shoot apical meristem. The new model was also shown to be able to produce a one-sided distichous pattern that is seen in phyllotaxis of a few plants of Zingiberales and has never been addressed in the previous model studies. These results implicated inductive as well as inhibitory mechanisms in phyllotactic patterning, at least in Zingiberales.
植物叶子在茎上的排列方式，称为叶序，表现出美丽而神秘的规律性，一直是生物模式形成最吸引人的课题之一。经过对叶序的长期研究，现在人们普遍认为，现有叶原基对新原基形成的抑制作用决定了叶序的模式。然而，姜目姜科特有的 Costaceae 具有螺旋单生性，其特征是具有小发散角的陡峭螺旋，这似乎与基于抑制作用的机制不一致，并且一直是一个“真正的难题”。我们提出了一个新的数学模型，假设每个叶原基不仅发挥抑制作用，还发挥一些诱导作用。当这两种效应满足一定关系时，用新模型进行的计算机模拟成功地生成了螺旋单生性模式。得到的螺旋单生性与观察到的 Costus megalobractea 的实际 Costaceae 叶序相匹配，特别是与茎尖分生组织增大相关的发散角减小。新模型还能够产生单侧二列性模式，这种模式在姜目植物中的少数植物中可见，但在前一个模型研究中从未涉及过。这些结果表明，在姜目植物中，至少在叶序模式形成中存在诱导和抑制机制。
