For in vivo observation of sieve tubes, cortical cell layers
were removed from the lower side of the main vein of a fully
expanded leaf, still attached to an intact plant, to provide a
CLSM observation window (Knoblauch and van Bel 1998). In
translocation experiments, phloem-mobile dyes were administered
to the cut midrib after having removed the leaf tip at a
distance of approximately 3 cm from the observation window.
In the other tests, fluorochromes were administered directly on
the bare-lying phloem tissues at the observation window. Observations
were performed using four healthy and four diseased
6-week-old plants, as soon as symptoms appeared on the
infected ones. The experiments were repeated on at least two
different leaves per plant.