The anatomy and ultrastructure of Pterodon pubescens primary pulvinus were studied to verify if slow leaf movements are associated with pulvinus cells features. Pulvini samples deriving from leaf with open and closed leaflets were prepared following usual techniques using light and electron microscopy. The pulvinus has a unisseriated epidermis covered by a thick cuticle and many trichomes, cortex with several layers of parenchyma cells (motor cells), a central vascular core surrounded by septate fibers, and a reduced pith. Cortical cells features change with the turgescence degree, showing alteration in the cell size and shape, cell wall thickness, frequency and arrangement of plasmodesmata, vacuole content and number and cytoplasm density. Septate fibers around the phloem were described for the first time in pulvini. The wide occurrence of plasmodesmata, the apoplastic barriers absence and the lignification scarcity (only present in xylem vessels) indicate a continuity, both simplastic and apoplastic, from the epidermis to the vascular tissue of the pulvinus. In Pterodon pubescens, primary pulvinus features are compatible with slow movement pulvini; the features shared to speedy movement pulvini are the presence of vacuoles with phenolic substances in the cortical cells and amiloplasts in the endodermal cells. Movements caused by P. pubescens primary pulvinus are associated with changes in both the apoplastic (wall infoldings) and symplastic (vacuolar reorganization).
anatomy; Fabaceae; Pterodon pubescens; primary pulvinus; ultrastructure
