In strongly self-incompatible genotypes of Gaudinia fragilis (L.) Beauv, and Secale cereale L., incompatible pollen grains germinate normally, but the tubes are arrested at or near the stigma surface. The response, which may occur within 30 sec of the emergence of the tube, seems to be contingent on contact between the tube tip and the surface secretions of the stigma. The suspension of tube growth is followed by the deposition of callose in the tube and the grain, but this is not the primary reaction. The earliest abnormality appears in the formation of the wall at the tube tip. The wall in the extending apex is composed of pectic microfibrils, contributed by the precursor particles (“P-particles”) present in the ungerminated grain. In an incompatible tube these do not flow into the wall to form the normal thin apical sheath, but accumulate to form nodules or lamellate aggregates. It is suggested that this is the direct consequence of contact with the stigma-held incompatibility factors, which may inhibit growth by cross-linking the microfibrils in such a way as to prevent their re-distribution and re-orientation. Individuals of Alopecurus pratensis vary in the strength of their self-incompatibility response. In some genotypes, self-pollen tubes penetrate the stigma surface and reach the transmitting tracts of the stylodia before they are inhibited. This behaviour provides a link with gametophytic selfincompatibility systems in other families, where the inhibition is normally in the transmitting tract of the style.

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Acta botanica neerlandica

CC BY 3.0 NL ("Naamsvermelding")

Koninklijke Nederlandse Botanische Vereniging

K.R. Shivanna, Y. Heslop-Harrison, & J. Heslop-Harrison. (1982). The pollen-stigma interaction in the grasses. 3. Features of the self-incompatibility response. Acta botanica neerlandica, 31(4), 307–319.