Self‐incompatibility in Papaver rhoeas: there is no evidence for the involvement of stigmatic ribonuclease activity

Abstract. Ribonuclease assays have revealed, in contrast to the self-incompatibility (SI) system of Nicotiana alata, there is no detectable ribonuclease activity that correlates with the presence of the functional stigmatic S-gene product in Papaver rhoeas. Thus, we have shown that the inhibition of incompatible pollen tube growth in P. rhoeas is not associated with ribonuclease activity. Furthermore, the finding that pollen from P. rhoeas, unlike that from N. alata, is insensitive to purified bovine pancreatic ribonuclease A at very high concentrations, suggests that the involvement of ribonucleases in the inhibition reaction of the SI response in P. rhoeas is unlikely. In addition, the level of ribonuclease activity in mature stigmas of P. rhoeas is very much lower than that in N. alata and significantly, the level of ribonuclease activity did not rise in conjunction with the developmental expression of SI. Therefore, as a result of these studies, we believe that SI in P. rhoeas does not involve ribonuclease activity.