Ultrastructural Aspects of Unilateral Interspecific Incompatibility betweenLycopersicum PeruvianumandL. Esculentum

Abstract

Observations have been made, at the electron microscope, of the pollen tubes present in the styles of Lycopersicum esculentum and L. peruvianum after reciprocal crosses between the two species. The unilateral incompatibility barrier which isolates the two species when L. peruvianum is used as pistillate parent was then compared to the processes of pollen tube rejection which have been recently analysed (J. Cell Sci., 1972) after self-pollination in this self-incompatible species. Such a comparison, which was also carried out by means of fluorescence techniques, has permitted to find out that for both types of incompatibility the rejection process was characterised by a progressive disappearance of the callose-rich inner wall of the pollen tube and by an accumulation of bi-partite particles in the tube cytoplasm. In the case of unilateral incompatibility, however, the tube outer wall is gradually disaggregated while the callosic inner wall remains quite thick at the tube apex, becoming thinner and finally opening only at the very tip of the apical zone. As a result of this complete degradation of the apical wall the cross-incompatible pollen tube merely opens in the stylar tissue and does not accomplish the bursting process which had been found so typical of the self-incompatibility reaction. These observations support the hypothesis that unilateral incompatibility is governed by a mechanism which is related but no identical to the one controlling self-incompatibility.