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Shape, rhythms and growth heterogeneities of a leaf : unfurling and nutation of Averrhoa carambola

Abstract : In plants, growth is essential to the shape regulation of developing organs. It is also the key for every plant to adapt to its environment. At the cell level, growth relies on a competition between the inner pressure of the cell and the rigidity of its cell wall. Heterogeneities of these quantities across the tissue can result in differential growth and lead to motions of the whole organ. These macroscopic motions can thus be read as an outward signal of the cellular mechanisms underlying shape regulation and growth itself. Here, we propose to take benefit from this link between growth and motions to gain a new insight on growth through a multiscale approach, from the organ to the cell wall. We focus on the compound leaves of Averrhoa carambola which display two marked motions, unfurling and nutation, widespread among developing leaves. First, we show that the shape of the leaf results from an active regulation of its macroscopic mechanical properties. The kinematics of the two latter motions are then compared to the associated growth. Doing so, we put forward the specific patterns of growth and differential growth underlying the development of the leaf. Based on these results, we build a kinematic model for nutation which, accordingly with previous findings, suggests the occurrence of local contractions during growth. At the cell wall level, our results reveal spatial heterogeneities of both its rigidity and biochemical status within the leaf. These heterogeneities might be consistent with the direction of the nutation.
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Submitted on : Monday, October 29, 2018 - 3:42:10 PM
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Mathieu Rivière. Shape, rhythms and growth heterogeneities of a leaf : unfurling and nutation of Averrhoa carambola. Physics [physics]. Université Sorbonne Paris Cité, 2017. English. ⟨NNT : 2017USPCC040⟩. ⟨tel-01907869⟩

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