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"Morphogenesis" refers to the formation of intricate patterns in nature
out of flat and symmetrical conditions; it appears on a wide range of
phenomena, from sand dunes to snowflakes and flowers. While biological
factors like genetics play a major role in biological morphogenesis,
physical forces also have a crucial impact on pattern formation. This
applies to the particular case of plants that we will look at with a
physicist eye. If one observes the development of organs in plants such
as leaves, the final shape will be perfectly regulated. For example,
most simple leaves will end up being perfectly flat, and most compound
leaves will end up growing perfectly straight. This posture regulation
is visually striking. How to explain it?
The originality of our approach lies in the observation of growth
induced plant movements. Although they were already observed as early as
400 years before common era by Androsthenos of Thasos, an admiral of
Alexander the Great who reported about the ``sleep movements'' of the
tamarind's leaflets, and later popularized by Darwin, the active motions
of plants have never been carefully exploited. In this talk, we will
focus on the slow growth induced movements observed for two model
plants: one simple leaf, and one compound leaf. By comparing our data to
simple phenomenological and geometrical models, we will show in both
cases that plant motions associated to mechanosensitivity are key
phenomena to explain posture regulation in plant development. |