Pseudo-self-compatibility in Ultraviolet-irradiated Plants of Primula Acaulis (‘pin’ morph)

Apoplastic peroxidase distribution in transmitting tissue of the stylar ‘neck’ was investigated using the DAB cytochemical reaction applied to electron microscopy in non-, self- and cross-pollinated pistils of Primula acaulis (‘pin’ morph) exposed or not to ultraviolet (u.v.) irradiation. In non-irradiated flowers, apoplastic peroxidase activity, which is present in non-pollinated pistils, is increased by self-pollination, whereas cross-pollination causes its disappearance from the central portion of the transmitting tissue. Apoplastic peroxidases localized in the central portion of the transmitting tissue are supposed to play a role in the predisposition of the pistil to reject incompatible pollen tubes and in the rejection mechanism itself. Pistil irradiation with u.v., which induces pseudo-self-compatibility, modified the aforementioned apoplastic peroxidase distribution. Shortly after u.v. irradiation of nonpollinated styles, apoplastic peroxidase activity was absent from the central portion of the transmitting tissue; some hours later peroxidase activity was restored, and 40 h after treatment, the ‘normal’ peroxidase distribution was observed. Our data suggest an u.v.-induced temporary removal of the ‘predisposition for incompatible pollen tube rejection. Moreover, soon after irradiation, the usually observed peroxidase production due to self-pollination was inhibited. Pseudo-self-compatibility, observed when self-pollination was carried out immediately after u.v. irradiation, was due to incompatible pollen tube elongation in a transmitting tissue devoid of apoplastic peroxidases and hindered in the rejection mechanism. However, pseudo-self-compatible pollen tube growth was not accompanied by the dramatic changes in transmitting tissue ultrastructure observed after compatible cross-pollination. The data indicate that, even if incompatible pollen tubes are not ‘rejected’, they are still ‘recognized’ and hindered in their absorption of cellular reserves from the transmitting tissue.