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.