Barley anther culture: The effect of position on pollen development in vivo and in vitro.

Locule structure and organization were studied in vivo and in vitro to determine whether the disposition of pollen within barley anthers affected the response of pollen in culture. Following release from the meiotic tetrads, juvenile barley microspores become peripherally organized around the locule, with the single pollen pore oriented towards the tapetum. Scanning electron micrographs of transverse sections from freeze fractured anthers showed that some microspores failed to locate the tapetal surface and occupied a position in the centre of the locule where they continued to develop as small, abnormal pollen grains (dimorphic pollen). Previous evidence has suggested that in some species dimorphic pollen could be the source of embryonic pollen in vitro. Cultured anthers frequently dehisced to reveal a mass of dividing pollen grains, however those anthers that remained intact retained the original locule structure and could be freeze fractured permitting examination of the developing pollen in situ. This showed that pollen embryogenesis was not restricted to dimorphic pollen, and that any grain could become Embryogenic irrespective of position.