Giant fluctuations in strain rate as part of normal leaf growth
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Giant fluctuations in strain rate as part of normal leaf growth Michal Sahaf, Eran Sharona The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, Israel Received: 10 January 2020 / Accepted: 26 September 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We report the effects of abrupt transitions of light intensity on the growth patterns and mechanical properties of young tobacco leaves. Changes in light intensity induce large variations in the leaf strain rate, which can be an order of magnitude larger than the average growth rates, and include both tissue expansion and shrinkage. These are accompanied by large changes in the tissue’s mechanical properties. Similar effects are observed in response to wind. We show evidence supporting the hypothesis that these effects originate from hydraulic mechanisms, i.e., variations in turgor pressure. In the context of growth patterns and growth regulation, we show giant fluctuations in strain rate to be a normal part of the growth process of leaves, which should be taken into account as a means for redistributing the stresses accumulated during the process of growth.
1 Introduction Leaf growth is known to be a noisy process [1], in which the local strain rates of epidermal cells vary in space and time. The epidermis cells are attached to their neighbors, so a single cell is unable to change its surface area dramatically, since the space it occupies also affects the size and shape of its neighbors. Still, fluctuations are observed, but they are evened out by mechanical and geometrical constraints, mediated through biological mechanisms, and resulting in a smooth average growth rate and reproducible shapes [2–4]. Therefore, in a healthy leaf and under normal conditions, only a relatively narrow range of average strain rates is considered possible. It is also well known that extreme conditions, such as drought, can influence growth rate [5], [6]. However, for plants which enjoy a constant supply of water and nutrients, major changes in the plant’s water content are not considered to be part of their normal growth process. Turgor pressure provides the driving force needed for growth, as formulated in the Lockhart equation [8] and more complex models [9], [10]. During the normal growth process, turgor pressure is considered to be in homeostasis, regulated to be either constant or following a periodic pattern [7]. Sudden, naturally occurring changes in water pressure and their possible effect on growth and morphogenesis have not been a focus of study so far.
Electronic supplementary material The online version of this article (https://doi.org/10.1140/epjp/s1336 0-020-00813-x) contains supplementary material, which is available to authorized users. a e-mail: [email protected] (corresponding author)
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Eur. Phys. J. Plus
(2020) 135:836
Plants in nature are exposed to changing light and wind conditions. Light intensity may change gradually, as the sun
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