Abstract: The effects of pear stylar S-RNase on compatible and incompatible pollen tube ultrastructure
in vitro were studied with transmission electron microscope. Ultrastructure of compatible pollen tube and con
trolwas natural during growth, i.e. cytop lasm and organelles filled tube growth tip and their configurations
were intact. There was no callose along the cell wall. While ultrastructure of incompatible tube degenerated
gradually followed by treatment time. After treated for 3 h incompatible tube was full of cytop lasm and organ
elles. There was no callose along the cell wall. But secreting vacuoles fused at the apex of tube and the cell
wall was thinner than that of others. Eight hours after treatment mitochondria appeared swelling, cristae de
creased or disappeared, ER dilated and wrapped around vacuoles and other organelles, vacuoles fused and
swallowed cytop lasm and organelles. After 24 h, mitochondria and ER disappeared, only a little of cytop lasm
laid near the tube tip and the shank nearlywere emp ty. Cellwalls became thicker and a layer of callose laid a
long the cell walls. The result hits pear stylar S2RNase could cause degeneration of incompatible pollen tube
and inhibited incompatible tube growth.

Key words: Pear, Self-incompatibility, S-RNase, Pollen tube, Ultrastructure