- Pulvinus
A pulvinus (pl. "pulvini") is a
joint -like thickening at the base of a plantleaf or leaflet that facilitates nyctinastic and thigmonastic movements. It consists of a core ofvascular tissue within a flexible, bulky cylinder of thin-walledparenchyma cells.Pulvinar movement is caused by changes in
turgor pressure leading to a contraction or expansion of the parenchyma tissue. The response is initiated when sucrose is unloaded from thephloem into theapoplast . The increased sugar concentration in the apoplast decreases thewater potential and triggers the efflux ofpotassium ions from the surrounding cells. This is followed by an efflux of water resulting in a sudden change of turgor pressure in the cells of the pulvinus. The process is similar to the mechanism ofstoma tal closure.Common examples for pulvinar movements include the night closure movement of
legume leaves and the touch response of the sensitive plant ("Mimosa pudica "). Nyctinastic movements (sleep movements) are controlled by thecircadian clock and light signal transduction throughphytochrome . Thigmonastic movements (touch response) appear to be regulated through electrical and chemical signal transduction spreading the stimulus throughout the plant.References
*P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): "Biology of Plants", 7th Edition, W.H. Freeman and Company Publishers, New York, ISBN 0-7167-1007-2
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