Pollen-Stigma Interaction Which Might Be Critical to the Gametophytic Incompatibility of Japanese Pear

A few fundamental experiments were carried out to increase information about the incompatibility of Japanese pear (Pyrus serotina R.).The results obtained are summarized as follows.1. Flowers of `Kosui' at anthesis were self-or cross-pollinated after emasculation, and pollen germination on stigmas at 6 h after pollination was observed.Pollen grains in cross-pollination germinated well and their pollen tubes elongated into stigmas by that time.But in selfpollination, the number of pollen grains observed on the stigma surface was very small and few pollen grains stretched their tubes into stigmas.Tube growth of cross-pollen was smooth in styles and some of the pollen tubes penetrated into ovaries 72 h after pollination.On the contrary, tube growth of self-pollen was very poor and most of the tube tips stayed around 2 mm below the stigma surface at 72 h after pollination.2. Flowers of `Kosui' and `Chojuro' at anthesis were emasculated, self-or cross-pollinated, fixed at intervals, stored in 70% Ethanol and processed for fluorescent microscopy through a routine procedure, where the number of pollen grains left adhered to the stigma surface was counted.On `Kosui', cross-pollination greatly surpassed self-pollination at 3 h after pollination.But the difference decreased as time went on and there existed no difference between self-and cross-pollination at 12 h after pollination.On `Chojuro', cross-pollination was superior to self-pollination from 6 to 12 h after pollination.3. Pistils of `Kosui' that were sampled soon after pollination were analyzed for proteins by IEF electrophoresis in combination with a silver nitrate staining procedure.Clear difference was observed between self-and cross-pollination as to the band pattern of buffer-soluble proteins of ovaries as soon as at 3 h after pollination.From these results, it was suggested that the stigma might play some significant role in the function of incompatibility of Japanese pear.