A second route via the desmotubule potentially involves diffusion along the ER membrane. Hydrophilic fluorescent lipids partitioned within the ER membrane were demonstrated to be able to move from cell to cell following photobleaching, in contrast to lipids inserted within the plasma membrane (Grabski et al. 1993). Similarly, the fluorescent probe DiOC6 was observed to move from cell to cell, presumably via the membrane of the desmotubule, in pea root cortex tissue (Schulz 1999). It appears that the plasma membrane, but not the desmotubule, within plasmodesmata is modified in such a way that it forms a barrier to the diffusion of lipids across plasmodesmata (Grabski et al. 1993).
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