Apoplastic transport of ions in the motor organ of Samanea

Abstract

Turgor-mediated leaf movements of the legume Samanea saman are associated with the migration of K' and Cl between opposing sides of the motor organs (pulvini). We have investigated the pathway of this ion migration by localizing K+ and Cl-within the secondary pulvinus at various times during leaf movements. Ion distributions in freeze-dried cryosections of pulvini were determined by scanning electron microscopy/x-ray microanalysis. The results indicate that the apoplast is a major pathway for the migration of K+ and Cl-within the pulvinus.Circadian and light-modulated leaflet movements of Samanea and other nyetinastic legumes result from massive rhythmic migrations of K+ and Cl-between opposing sides ofspecialized motor organs, the pulvini (1-4). These ion movements mediate localized changes in the volume of motor cells, causing the pulvinus to alter its shape. In the daytime position, pinnae (leaflets) of the bipinnate leaves of Samanea are separated from each other in a horizontal plane (open). At night the pinnae are folded together in a vertical position (closed). Leaflet closure occurs when cells on the flexor side of a pulvinus increase in volume while those on the opposite (extensor) side lose volume (5). These motor cell-volume changes are reversed when leaves reopen in the morning. The leaflet movements and the causal ion migrations are controlled by an endogenous clock and its interaction with light absorbed by the photo-convertible pigment phytochrome (1,3,(6)(7)(8)(9).The shuttling of K+ and Cl-between the extensor and flexor regions of pulvini has been documented by the use of an electron microprobe (1-3). However, the technique lacked the spatial resolution necessary to assess the pathway of this solute redistribution. Because plasmodesmata (intercellular cytoplasmic bridges) were present in all examined regions ofthe motor tissue (10), the symplast (the living continuum) and the apoplast (the nonliving continuum ofcell walls and intercellular spaces) both apparently are available for the lateral movement of ions in the pulvinus. Determining the relative importance of these two possible pathways would further our understanding of the mechanism of leaf movements.We have investigated the route of ion migration by using scanning electron microscopy/x-ray analysis to measure the K+ and Cl-contents of the symplast and apoplast at various stages of leaf movements. Cryotechniques. Freeze-dried thin sections of pulvini were prepared by using methods designed to minimize redistribution ofdiffusible ions during sample preparation. Secondary pulvini, which join pinnae to the rachis, were excised from plants, trimmed to a size of about 1 mm3, and mounted on the heads of silver pins (LKB 94-92-0592) with a drop of Tissue-Tek. The pins were then inserted into a spring-loaded gun (LKB) and shot into supercooled Freon-22 (-1500C) prepared according to Somlyo et al. (11). Total elapsed time from pulvinus excision to freezing was 30 sec or less. The frozen samples were stored in liquid nitrogen until they co...

Anatomia e ultra-estrutura do pulvino primário de Pterodon pubescens Benth. (Fabaceae - Faboideae)

“…(Satter et al 1982) e Robinia pseudoacacia L. (Moysset & Simón 1991). A ausência de barreiras apoplásticas, especialmente lignificação das paredes celulares e a abundância de plasmodesmos indicam que ambas as vias, apoplástica e simplástica, são usadas na redistribuição de íons durante os movimentos foliares, como sugerido por diversos autores (Morse & Satter 1979, Campbell et al 1981, Satter et al 1982, Moysset & Simón 1991.…”

Polyamine Oxidase in Oat Leaves: A Cell Wall-Localized Enzyme

“…What possible role could polycationic polyamines have in the apoplast? It is significant that cellulosic walls with high negative charge densities can bind large quantities of cations (6), and that such an apoplastic continuum probably serves as a pathway for ion transport between flexor and extensor motor cells of leguminous pulvini (3). Thus, metabolism of polycationic polyamines might furnish a regulable and variable parameter for influencing and changing the flux of such important ions as Ca2+ and K+ in cell walls.…”

Extensor and Flexor Protoplasts from Samanea Pulvini

“…However, even with high resolution techniques that distinglish between elements in the wall and the protoplasm (4,20), there is a danger of ion migration during specimen preparation. In experiments that measure ion extrusion or uptake by excised strips of tissue (10), the wall can act as a buffer that affects the magnitude and kinetics ofobserved changes.…”