The genetics of self-incompatibility in Oenothera rhombipetala

Late-acting self-incompatibility--the pariah breeding system in flowering plants

It is estimated that around half of all species of flowering plants show self-incompatibility (SI). However, the great majority of species alleged to have SI simply comply with 'the inability of a fully fertile hermaphrodite plant to produce zygotes when self-pollinated'--a definition that is neutral as to cause. Surprisingly few species have been investigated experimentally to determine whether their SI has the type of genetic control found in one of the three established mechanisms, that is, homomorphic gametophytic, homomorphic sporophytic or heteromorphic SI. Furthermore, our knowledge of the molecular basis of homomorphic SI derives from a few species in just five families--a small sample that has nevertheless revealed the existence of three different molecular mechanisms. Importantly, a sizeable cohort of species are self-sterile despite the fact that self-pollen tubes reach the ovary and in most cases penetrate ovules, a phenomenon called late-acting self-incompatibility (LSI). This review draws attention to the confusion between species that show 'self-incompatibility' and those that possess one of the 'conventional SI mechanisms' and to argue the case for recognition of LSI as having a widespread occurrence and as a mechanism that inhibits selfing and promotes outbreeding in many plant species.

Temperature effects on self incompatibility in Lilium longiflorum

Detached pistils of the clonal variety, Lilium longiflorum 'Aral No. 5', were submerged before pollination in 50°C water for 0, 1, 2, 3, 4, 5, 6 or 7 min and then immediately compatibly and incompatibly pollinated. Incompatibility, as indicated by pollen tube length after 48 h at 23.5°C, was eliminated by a 1-2 min submersion while compatibility was removed by a 4-5 min one. The 'window' of incubation temperatures at which incompatible and compatible pollen tubes are clearly differentiated occurred between 15 and 30°C.

[Plastome dependent pollen sterility inOenothera]

Pollen in which the genome complexesflavens (derived fromOe. suaveolens) orgaudens (derived fromOe. lamarckiana) are combined withparviflora plastids (plastome IV) fails to germinate even though it is well developed otherwise. This inability to germinate, however, is not always complete. Those exceptional pollen grains which do germinate do not get this ability by a change of their genome. The germination rate varies modificatively. Furthermore it has clearly been demonstrated that the degree of sterility is influenced by the genotype of the sporophyte. But this influence of the diploid sporophyte on the haploid gametophyte does not go as far as to completely suspend differences in germination behaviour of pollen with plastome IV on the one hand and of (normal) pollen with other plastome types on the other hand.