Migration of Calcium and Its Role in the Regulation of Seismonasty in the Motor Cell of Mimosa pudica L.

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Abstract
Volume and conformational changes of the contractile tannin vacuoles of the abaxial motor cells of the primary pulvinus of Mimosa pudica L. parallel the seismonastic leaf movement. Since such changes in cells and organelles of animal systems are often regulated by calcium, we studied Ca2+ movement in the motor cells and tissue. By fixation with Lillie's neutral buffered formalin, followed by staining with alizarin red sulfate (ARS), calcium was localized in the tannin vacuoles of the motor cells of the primary pulvinus. After treatment with ethylenediaminetetraacetate, 8-hydroxyquinoline, and several other calcium-complexing or extracting agents, the color reaction due to alizarin red sulfonate was no longer present. By using an analytical method, it was shown that the effluent from stimulated pulvini has significantly more Ca2+ than that from unstimulated controls. Ten millimolar LaCl3 inhibits recovery of the tannin vacuole in vivo in 10 mm CaCl2 or in distilled water. Quantitative data obtained by microspectrophotometry demonstrated calcium migration during the bending movement of the primary pulvinus. In the adaxial motor cells a small amount of calcium migrates from the tannin vacuole, and calcium on the cell wall moves to the central vacuole. In the abaxial half, a large amount of calcium from the tannin vacuole moves to the central vacuole of the motor cell. It is probable that the calcium binds to the microfibrillar contents of the central vacuole. These observations support the contention that Ca2+ migrates between the surface of the tannin vacuole and the inside of the central vacuole. The recovery and maintenance of the tannin vacuole in the spherical form may play a role in maintaining turgor in the motor cells of the abaxial half of the primary pulvinus of Mimosa.