Ultrastructural Aspects of Nuclear Behaviors of Pleurotus ostreatus - Behaviors of Astral Microtubules During Hyphal Development -

Premitotic, mitotic and postmitotic nuclei in the dikaryotic somatic hyphae of Pleurotus ostreatus, the oyster mushroom fungus were ultrastucturally examined using chemical fixation and freeze-substitution process, and the behaviors of astral microtubules associated with these nuclei were closely analyzed. Electron microscopic examinations revealed that astral microtubules are significantly abundant when the nuclei are in the stage of migration and at the stage of migration, the separation of spindle pole body occurs. Such an abundancy of astral microtubules in premitotic migrating nuclei is well contrasted with mitotic and postmitotic nuclei with much fewer astral microtubules and it should be noted that neither of these latter classes of nuclei exhibits the separation of the spindle pole body. It is remarkable that the postmitotic nuclei that are believed to migrate actively are associated with the astral microtubules that are less in numbers and length. During all the stages of nuclear division, astral microtubules are invariably radiating from the spindle pole bodies and nucleolus remains within the nuclear envelope of dividing nuclei throughout the division. The functions of astral microtubules developed during the nuclear division as well as the nuclear migration and separation of the spindle pole body were closely examined.