pulvinus

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pulvinus

a mass of thin-walled cells at the base of the leaf petiole in certain plants, forming a swollen area surrounding the vascular tissue. The pulvinus is subject to large changes in TURGOR. For example, in the runner bean the pulvinus is turgid during the day and supports the petiole, so that the leaf is held outwards. At night the pulvinal cells loose turgidity and the leaf droops. These diurnal leaf positions are sometimes called sleep movements. The sudden change in leaf posture observed in Mimosa sensitiva when touched is also controlled by pulvinal cells.
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For light-harvested pulvini, the terminal and lateral pulvini from the second through sixth trifoliolate leaves were separately excised with a razor one to three hours into the light period and frozen in liquid nitrogen; dark-harvested pulvini were harvested one to two hours prior to the end of the dark period.
Table 1: Differentially Expressed Proteins in Light and Dark Harvested Soybean Pulvini
Vegetative flushes are the most abundant infection sites for the witches' broom pathogen (Sreenivasan and Dabydeen, 1989); however, petioles, pulvini, and stems are also susceptible to infection (Cronshaw and Evans, 1978).
The leaflet movements are brought about by motor organs (or "pulvini") localized at the leaflet bases and are induced by transferring leaves from light to darkness (scotonasty) or from darkness to light (photonasty).
While there are a number of long-appreciated examples of gravitropism involving intact higher plants (Larsen, 1962; Firn & Myers, 1987; Salisbury, 1993) and higher fungi (Moore, 1991), and even explanted organs such as the pulvini of grasses (Kaufman et al., 1995), that may be identified as candidate test systems for studying differences after exposure to changes in gravity, there is relatively little known about cells outside the plant body (Moroz, 1984; Todd, 1989, 1991).