Changes in Morphometry and Elemental Composition of Robinia pseudoacacia Pulvinar Motor Cells During Leaflet Movements

Abstract

Changes in shape and size of Robinia pulvinar cortical cells in relation to leaflet movements have been investigated using an image processing system applied to drawings of transverse and longitudinal pulvinar sections. Both the size and shape of cell sections underwent change during movement. The dorsal-left side region of the cortex has been characterized as the extensor region which increases turgor during opening. Morphometric changes occur throughout the cortical motor cells except in the three or four inner layers. K, Cl, S, and Ca distribution in cell walls and protoplasts of inner and outer motor cells have been measured with X-ray microanalysis. The distribution pattern of K and Cl shows that these ions are mainly responsible for turgor changes. K and Cl were simultaneously depleted in apoplast and protoplast, which suggests that cell walls do not possess a high enough ionic reservoir during Robinia leaflet movements. Ca was always higher in flexor cell walls than in extensor regions of closed pulvini. This fact could be related to a lower ability to extend of flexor cells which underwent fewer morphomertic changrs during movement.