Evidence for DNA fragmentation triggered in the self-incompatibility response in pollen of Papaver rhoeas

Studied of the molecular and biochemical basis of self-incompatibility (SI) in Papaver rhoeas have revealed much about the signalling pathways trigger ed in pollen early in this response. The aim of the current investigation w as to begin to study downstream events in order to elucidate some of the la ter cellular responses involved in the SI response and identification of th e mechanisms controlling the irreversible inhibition of pollen tube growth. We have used the FragEL assay to investigate if there is any evidence for DNA fragmentation stimulated in pollen of P, rhoeas in an S-specific manner . Our data clearly demonstrate that S proteins are responsible for triggeri ng this, specifically in incompatible, and not compatible, pollen. DNA frag mentation was first detected in incompatible pollen tubes 4 h after challen ge with S proteins, and continued to increase for a further 10 h. This prov ides the first evidence, to our knowledge, that this phenomenon is associat ed with the SI response. We also demonstrate that mastoparan, which increas es [Ca2+](i), also triggers DNA fragmentation in these pollen tubes, thereb y implicating an involvement of Ca2+ signalling in this process, Together, our data represent a significant breakthrough in understanding of the SI re sponse in Papaver pollen.