Gametophytic self-incompatibility re-examined: a reply

The use of freeze-substitution and LR gold in the study of rye grass (Lolium perenne) pollen

Pollen grains of Lolium perenne (rye grass) were prepared for transmission electron microscopy by rapid freezing in liquid propane, substitution in acetone, methanol or diethyl ether, and embedment in the acrylic resin London Resin gold. These were compared to pollen chemically fixed (CF) in aldehyde/osmium tetroxide and embedded in the epoxy resin Quetol 651. Ultrastructural preservation was superior in freeze-substituted (FS) pollen, particularly with the use of acetone or methanol. Optimally preserved FS pollen displayed a homogeneous aspect of the cytoplasm and nucleoplasm, and smooth, uninterrupted contour or organelles. A striking difference was also seen in the preservation of inclusions in the intine. Varied forms and sizes of intine inclusions were evident in FS pollen but these were not discernible in the CF image. The FS scheme studied here presents enormous potential for both ultrastructural and immunolabelling studies in rye grass pollen. Problems discussed include artifacts associated with each of the substitution solvents used, and a gradient of freezing damage observed within the pollen grain.

On the evolution of genetic incompatibility systems. III. Introduction of weak gametophytic self-incompatibility under partial inbreeding

I explore the proposition that genetic incompatibility systems serve as a means for parents to evaluate and discriminate among their own offspring. Conditions for the initial increase of gametophytic self-incompatibility in a self-compatible population undergoing selfing, sibmating, and random outcrossing are reported. The adaptive value of reducing the concordance between offspring and maternal genotypes depends upon the relative changes in the numbers of offspring derived by the three modes, parent-offspring relatedness, and the magnitude of distortion of transmission ratios through pollen. Recessivity of stylar expression and low rates of receipt of pollen from related individuals facilitate the evolution of self-incompatibility. Viewed as a means of preferential maternal investment in offspring of high quality, self-incompatibility may be regarded as serving a function in common with diverse phenomena, including sexual selection, brood reduction, and other forms of prezygotic and postzygotic incompatibility. Associations between incompatibility loci and loci expressing inbreeding depression are expected to improve the reliability of the level of concordance at incompatibility loci as a measure of genomic homozygosity and offspring quality.

"Egg transformation" induced by irradiated pollen in Nicotiana: critical appraisal of Chyi and Sanford's observations

This note strongly refutes the suggestion by Chyi and Sanford (1985) that "egg transformation" by the use of lethally irradiated pollen in Nicotiana reported by the present author could be explained on the basis of mutation, contamination or other causes, and suggests that their conclusion is based on faulty experimentation and interpretation. It also shows that, contrary to these authors' assertions, their results, in fact, contain certain significant demonstrations of egg transformation supporting the present author's work.