Complex Carbohydrates at the Interacting Surfaces during Pollen-Pistil Interactions in Nicotiana alata

Abstract

As part of a broad programme to study the molecular basis of fertilization, we have investigated the complex carbohydrates at the interacting surfaces of the pollen tube and pistil in Nicotiana alata (Solanaceae), an ornamental tobacco. This plant exhibits gametophytic incompatibility and self-incompatibility genes (S-genes) operate to prevent in-breeding. Pollen behaviour is controlled by its own genotype and pollen tubes are arrested if the allele carried by the pollen matches one of the two alleles in the pistil tissue (for review see de Nettancourt 1977). In a compatible mating, pollen grains germinate on the surface of the stigma and produce pollen tubes which penetrate the surface of the stigma and grow through the central solid transmitting tissue of the style to the ovary. As the pollen tube grows, callose plugs are laid down at regular intervals cutting off the growing tip from the spent pollen grains; this gives the pollen tube a ladder-like appearance. At maturity, the transmitting tissue cells are elongated and connected by plasmodesmata at their transverse walls into vertical files which are separated by secreted intercellular matrix material through which the pollen tubes grow. In contrast, in an incompatible or self mating, growth of the pollen tube is arrested just below the stigma, in the top 2–3 mm of the style. The tips of the inhibited pollen tubes swell and sometimes burst; there is also a characteristic deposit of callose immediately behind the tip.