Pollen-Pistil Interaction and Fertilization

Abstract

Pollen-pistil interaction covers the sequential events from pollination until the pollen tubes enter the ovules. During this interaction the pistil screens the pollen grains. Pollen of other species are inhibited at the level of pollen germination or pollen tube growth in the style. Conspecific pollen grains are recognized by the stigma and activate physiological processes to facilitate their germination and pollen tube growth. In self-incompatible species, even self-pollen are recognized and inhibited. Only compatible pollen grains which are most vigorous are selected for fertilization. Thus, there is a close dialogue between the gametophytic partners (pollen grains and pollen tubes) and the sporophytic partner (the pistil) during pollen-pistil interaction. Extracellular components present in and on the pollen wall and on the stigma and along the path of the pollen tube in the style are involved in pollen recognition and their subsequent promotion/inhibition. Some of the genes/gene products involved in these interactions have been identified in recent years in a few model systems. After entering the ovary, pollen tubes are guided towards the micropyle of the ovule by the attractants secreted by the synergids of the embryo sac (ES). The nature of these attractants is known in some model systems such as Torenia and Arabidopsis. The pollen tube enters the ES through one of the synergids and discharges the two male gametes for fertilization. Some of the coordinated details amongst the cells of the ES in orchestrating pollen tube guidance, release of male gametes, double fertilization and cessation of the secretion of pollen tube attractants are discussed.