Development of the male gametophyte of an infertile plant Armoracia rusticana Gaertn.

Horseradish, Armoracia rusticana , is propagated vegetatively through root cuttings. It is described as a male-sterile plant as it does not form seeds or only develops them in small quantities. This study discusses the anatomical structure of anthers and the events throughout meiosis up to the formation of a male gametophyte. Microscopic observations have shown that the anatomical structure of the anther wall of A. rusticana is typical of the whole family of Brassicaceae , and all its layers are properly developed and fully functional. Meiosis in the sporogenous tissue proceeds correctly and leads to the formation of microspores. Also the configurations of the cytoplasmic skeleton are typical of plants with simultaneous cytokinesis. Further development, however, exhibits many abnormalities. A majority of the cells formed in the sample studied were dysfunctional uninucleate microspores with apparent symptoms of degeneration of the cytoplasm and organelles. Binucleate pollen grains, in which mitosis did occur, constituted only 10% of the cells analysed. Anatomical and cytological observations of male sterility in A. rusticana indicated inhibition of development at the microspore, stage which was manifested by cytoplasm degeneration with a low number of membranes and a scarce amount of starch in proplastids. Usually, in the prolonged microspore stage and in the young pollen no mitosis occurs at the time of anthesis. Cytological disorders may, to a great extent, limit the number of functional bicellular male gametophytes. Both in microspores and in pollen grains, there is exceptionally little starch in plastids.