CELL-TO-CELL TRANSPORT VIA MOTILE TUBULES IN GROWING HYPHAE OF A FUNGUS

The system of pleiomorphic, motile tubules and vacuoles in growing hyp hal tips of Pisolithus tinctorius has been shown to play a role in int racellular transport. Here we show that the same system also exchanges material between adjacent cells. This exchange is most obvious betwee n terminal and penultimate cells following nuclear division in the tip cell and just before dissolution of the cell wall between the clamp c onnection and penultimate cell. At this stage the two new dolipore sep ta are complete. The process was studied in living hyphae using confoc al and conventional fluorescence microscopy. Tubules could move in eit her direction across the septum and often extended and retracted sever al times and penetrated for some distance (e.g. 40 mum) into the recei ving cell. Movements appeared co-ordinated and during the exchange tub ules transiently inter-connected vacuoles in adjacent cells and by per istaltic movements appeared to transfer material between them. The flu orescent tubules occupied a specific plane in the vicinity of the sept um and remained in this plane for the duration of their movement, sugg esting that their orientation and direction of movement is controlled. In freeze-substituted hyphae, tubular cisternae of similar dimensions to fluorescent tubules passed through the parenthesome pores perpendi cular to the septum and in some cases entered the mouth of the septal pore. This indicates that the septal pore is of an appropriate dimensi on to accommodate the tubules and that they can cross the septal pore to exchange material between vacuole systems of adjacent cells. This i s the first direct demonstration of such intercellular transport via a sub-cellular compartment.