Cytoplasmic Streaming as an Intracellular Conveyer: Effect on Photosynthesis and H+ Fluxes in Chara Cells

Abstract

Giant-sized cells, such as the internodes of characean algae, demonstrate rapid (up to 100 μm/s) rotational cytoplasmic streaming that participates in long-distance intracellular interactions and coordinates the functional activity of organelles under a nonuniform light environment. The specific functions of intense cytoplasmic streaming remain poorly investigated. The lateral transport of photometabolites can be detected by combining pinhole illumination with measurements of chlorophyll fluorescence and external pH on microscopic cell regions located downstream of the locally illuminated area. The involvement of cyclosis in regulation of photosynthesis and plasmalemmal H+ transport was revealed by this means. In regions exposed to bright local light, the chloroplasts export reducing equivalents and triose phosphates into the streaming cytoplasm that spread over the cell and induce a transient rise of chlorophyll fluorescence in shaded cell areas located far from the site of photostimulus application. This review highlights the properties of cyclosis-mediated fluorescence changes, including the photoinduction of long-distance transmission, sensitivity to metabolic inhibitors, its nonuniform spatial distribution in illuminated cells, and gradual (1–5 min) inactivation of long-range signaling after transferring the cell to darkness. A stimulatory influence of the action potential on long-distance signal transmission is shown. The new method is suitable for studying the intercellular transport of metabolites and the permeability of plasmodesmata.