Characterization of theEgeria densa leaf symplast: Response to plasmolysis, deplasmolysis and to aromatic amino acids

Summary

The fluorescent dyes 6-carboxyfluorescein and fluorescein glutamylglutamic acid, which move freely in theEgeria densa leaf symplast, fail to move from cells subjected to plasmolysis, demonstrating that plasmolysis disrupts symplastic continuity. Dye movements begins again within 10 minutes of removal of the osmoticum and becomes more extensive with increasing recovery time. The re-established symplastic links show a number of distinctive features compared to untreated leaves: dyes of up to 1678 dalton can pass, compared to the normal limit of 665 dalton; and Ca²⁺ ions, which completely inhibit dye movement in untreated cells, only reduce the extent of dye movement. Aromatic amino acids and their fluorescein conjugates prevent intercellular movement in untreated cells. In deplasmolysed cells the aromatic conjugates move freely. The increased symplast permeability persists for at least 20 hours. Thus, after plasmolysis followed by deplasmolysis, the symplast shows a marked increase in permeability associated with an increased molecular exclusion limit, indicating an increase in pore size, and symplast permeability becomes relatively insensitive to Ca²⁺ ions or to the aromatic conjugates.