Induction of Deformed Pollen Tube Tips and Their Morphological Characteristics in Self-incompatible Japanese Pear.

Abstract

Aberrations in pollen tube tips of Japanese pear, Pyrus serotina, in vivo studies following pollen-incompatible and -compatible pollinations; and in vitro studies on the effects of chemical additives to the growth medium were investigated.Incompatible and compatible pollen/stigma-style combinations resulted in pollen tubes with deformed tips which were mainly detected as a swelling. The incompatible combinations developed approximately twice as many swollen tips. Their surface structure revealed irregular features such as concave and unusual furrows, whereas a smooth surface was observed in normally growing tips.In in vitro trials, ABA, ovarian extract (OE), polyethylene glycol (PEG), H3B03 and fusicoccin (FC) increased the number of abnormal pollen tube tips. The tip surfaces of these tubes were considerably irregular, except in the case of H3BO3, which seemed to be similar to those deformed tips observed in incompatible styles. Boric acid caused regular fine furrows along the tube axis but CaCl2 had no effect on the deformed tip formation; the tube surface structure was relatively smooth. Thus, the growth inhibitors tend to induce irregularities on pollen tube surface similar to those observed on pollen tubes growing in an incompatible style, whereas growth promoters did not induce such symptoms. The similarities in tip morphology may indicate that cell wall synthesis in pollen tubes growing in incompatible styles is altered by inhibitors or water stress following a specific recognition reaction on the stigmatic surface and/or in the transmitting tissue. This alteration causes cessation of tube growth.