ИСТИНА

Cellular communication involving fluidic active transport play anessential role in functioning of living organisms. Transcellular permeation and long-distance transport of solutes are important in plants because they deliver the photosynthetic assimilates to growing cells. Cytoplasmic streaming has long been conjectured to aid in overcoming the slowness of diffusion, but its precise role in metabolic function remains still unclear. The cells of characean algae represent an excellent example of an interlinked living microfluidic system to study the relation between cytoplasmic streaming, long-distance intercellular communication and their physiological function. A new method employing modulated chlorophyll fluorometry was developed to study plasmodesmal permeation by naturally produced photometabolites and to elucidate physiological means for modulation of cell-to-cell conductance. The method is based on cyclosis-dependent distribution of metabolites produced in brightly illuminated chloroplasts and exported to the cytoplasmic flow. The products released from chloroplasts travel with the streaming liquid and enter the chloroplasts in shaded areas. The entry of reducing substrates into the chloroplast stroma modulates photosynthetic electron flows, thus causing a transient increase in chlorophyll fluorescence due to a temporal reduction of the primary quinone acceptor QA in photosystem II. The results show that the plasmodesmata are permeable to low-molecular photometabolites. The time required for crossing the intercellular barrier was determined and used to estimate the coefficient of metabolite diffusion inside plasmodesmata. The intercellular transport was highly sensitive to moderate changes in external osmolarity and cell turgor. The inhibition of cell-to-cell transport under osmotic treatments was reversible and specific.