Pollen-Pistil Interaction

Pollen-pistil interaction is the entire sequence of physiological events that begins the moment a pollen grain lands on the stigma (a sporophytic tissue) and continues until the pollen tube finally enters the ovule and reaches a synergid, that is, everything spanning pollination through to the threshold of fertilization. Pollination itself is not selective: pollen of the wrong species, or otherwise incompatible pollen, frequently lands on a stigma along with compatible pollen. The pistil, however, has an in-built ability to recognise compatible pollen of its own species and to accept it, while rejecting incompatible or wrong-species pollen, a form of biochemical screening carried out by specific recognition proteins on the pollen surface and the stigma surface, which together determine compatibility or incompatibility.

Once recognised as compatible, a pollen grain absorbs water and nutrients from the stigmatic surface, germinates, and puts out a pollen tube. The stigma supplies conditions essential for successful germination that the pollen grain cannot provide for itself. As the pollen tube grows down through the tissue of the style, its direction and rate of growth are guided by specific chemical signals; eventually it is guided all the way to the ovule and, ultimately, into the embryo sac. Because many compatible pollen grains typically germinate simultaneously on one stigma, intense competition develops among their pollen tubes to be the ones that successfully achieve fertilization.

Pollen germination can also be induced artificially, outside the plant, in a synthetic culture medium; sucrose promotes pollen germination and pollen-tube elongation in vitro, and the addition of boric acid further facilitates and accelerates germination. …