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Sleep-like behaviour in a sentitive plant (Mimosa Pudica).

Topic: A. Basic Sleep Science - 5. Physiology
Track: Track 4: Sleep mechanisms and functions
Title: Sleep-like behaviour in a sentitive plant (Mimosa Pudica)
Author(s): S. Varani, T. Banfi, R. Biancotti, P. Orsini, L. Rocchi, P. d'Ascanio, U.
Institute(s): University of Pisa, Pisa, Italy
Text: Background: Sleep is behaviorally acknowledged as a vigilance state
characterized by a) a species-specific posture b) behavioral quiescence c) an elevated
arousal threshold d) state reversibility with stimulation (Campbell and Tobler, 1984).
Although this definition has been confined to animals, all features of sleep could be
applied to other organisms lacking a nervous system but still capable of movements,
and responsive to external stimuli. In this perspective, we investigated
whether Mimosa Pudica, also called Sensitive Plant, does fulfill the criteria for sleep.
The behavior of M.Pudica is characterized by nastic movements in response to light,
thermic and mechanical stimuli. Therefore, it seems a valid candidate to formally test
the presence of a sleep-like behavior.
Methods and Materials: 23 adult plants (1 year old) were kept indoor in constant
temperature and humidity conditions, under a 12h light/12h dark cycle (lights on at 8
a.m.). We constantly recorded the spontaneous movements of M. Pudica (n=10)
under continuous video-monitoring. Spontaneous movements were quantified by i) a
local manual index of single petiole tracking and i) a global automatic movement
index. In another set of experiments, the response threshold to mechanical stimuli
was tested via controlled air-puffs. For each plant (n=14) we set 3 different pressure
levels (low, medium and high) and visually scored the extent of the induced
Results: There was a significant difference between spontaneous movements
during the light (16.181±1.459 a.u.) and the dark phase (13.029±0.741 a.u, p=0.004,
Mann-Whitney), when the plant took a typical posture (upright state) raising its
petioles to the greatest extent. During this phase the spontaneous movements were
at their lowest value.
In parallel, the plant motor response to air puffs slowly decreased during the day.
From 8 a.m. to 2 p.m. M.Pudica showed its peak responsiveness (1.876±0,187 SE),
while at night (12 a.m.-8 a.m.) its lowest (0,421±0,104 SE), revealing a significant
difference in responsiveness between the night and every other period (p< 0.05,
Kruskal-Wallis). Moreover, in a subset of experiments (n=7) we observed an
increased response threshold at night (12a.m.-4 a.m.) as compared to the morning
(8 a.m.-2 p.m.; 1,5±0,4 versus 1,1±0,14 a.u., p=0.045, paired t-test).
Conclusion: In M. Pudica two of the criteria necessary to define sleep as a
behavioral state are satisfied.
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