Two-step mechanism of spiral phyllotaxis

Takuya Okabe; Jin Yoshimura

doi:10.1016/j.jtbi.2020.110484

Two-step mechanism of spiral phyllotaxis

J Theor Biol. 2021 Jan 7:508:110484. doi: 10.1016/j.jtbi.2020.110484. Epub 2020 Sep 10.

Authors

Takuya Okabe¹, Jin Yoshimura²

Affiliations

¹ Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8561, Japan. Electronic address: okabe.takuya@shizuoka.ac.jp.
² Department of International Health and Medical Anthropology, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan; Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan; The University Museum, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan; Marine Biosystems Research Center, Chiba University, Uchiura, Kamogawa, Chiba 299-5502, Japan; Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, Syracuse, NY 13210, USA.

PMID: 32918923
DOI: 10.1016/j.jtbi.2020.110484

Abstract

Fibonacci numbers such as 5, 8, and 13 occur in the spiral arrangement of lateral organs at shoot tips in plants. While the cone scales of conifers are normally arranged in 5 and 8 (or 8 and 13) curved rows in opposite directions, other numbers such as 4 and 7 (or 7 and 11) are found anomalously. The observed numbers still obey the Fibonacci rule, with the next number being the sum of the preceding two. Although these observations have been made for centuries, the underlying mechanisms of the numerical relationship have not been investigated. Here, we show that this phenomenon is caused by a two-step mechanism: (1) maintenance of a constant angle between consecutive lateral organs and (2) strong canalization of this angle to a specific value. The first step of the mechanism precedes the second step of the mechanism because the Fibonacci-rule pattern is due to the first step, while the second step distinguishes normal, anomalous and unobserved types. The current dominance of the normal type is a result of the evolutionary process of the second step.

Keywords: Canalization; Convergent evolution; Epigenetics; Parallel evolution; Plant morphology.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Models, Biological*
Plant Leaves*
Plants