Our knowledge of reproductive development in plants is essentially confined to herbaceous species. Very few studies deal with woody plants and none on willow. Willow is rapidly coming to the forefront as biomass species not only because it is fast growing, but also because of its high potential for bioproducts and bioenergy. As part of the program on developing willow as a model for reproductive development in woody species, this project specifically describes the structural events leading to the formation of pollen grains. In the course of the study, several developmental abnormalities were observed from Salix discolor clone S365. Abnormalities were based on comparison of histological structures of all developmental stages involved in pollen development using several clones and species of willow. The abnormalities observed in clone S365 includes a combination of the following: delayed tetrad formation, rare occurrence of tetrads, highly variable sizes of pollen grains, almost zero pollen viability, and stickiness of pollen grains resulting in their inability to be released. There were no abnormalities observed on the structure and development of the tapetum and anther wall. The structural analysis led us to examine meiosis and as a result, several meiotic irregularities were observed including delayed meiosis, presence of sticky chromosomes and occurrence of lagging chromosomes. The latter resulting in aneuploidy. Therefore, the sterility in S. discolor (S365) is genetic and not environmental, as previously thought. One dimensional gel analysis of proteins isolated from catkins containing microspore mother cells of normal and male sterile clones revealed an interesting difference that could point to the gene responsible for male sterility in willow.

Key words: male sterility, meiotic abnormalities, pollen development, reproductive development, willow, woody species