A Developmental Study of the Structure and Pollen Receptivity of the Macadamia Pistil in Relation to Protandry and Self-Incompatibility

The anthers of macadamia flowers dehisced 1-2 days pre-anthesis, but the stigma did not support pollen tube growth until 1-2 days post-anthesis. Esterase activity and extracellular secretion of carbohydrate, lipid, protein, and phenolics reached a peak at 1-2 days post-anthesis. The transmitting tract of the macadamia pistil had a complex structure with four distinct cell types with typical glandular ultrastructure. The stigma papillae and transmitting tissue (TT) cells at the base of the style had simple walls; the two types of TT cells in the upper style had labyrinthine wall thickenings. The inner TT cells of the upper style had thickenings on all walls from an early stage of development, whereas the outer cells had thickenings that developed following anthesis on the walls facing inner cells only. The thickenings of the outer, but not of the inner, cells stained for protein and phenolics. The pollen tubes grew between the inner and outer TT cells, and incompatible tubes were inhibited in this region. Inhibited pollen tubes had stacked endoplasmic reticulum and swollen tips with callose plugs and discharged contents.