An electron microscopic study of meiosis and the spindle pole body cycle in the smut fungus Sphacelotheca polygoni-serrulati

Abstract

An electron microscopic study was made of meiosis and the meiotic spindle pole body (SPB) cycle in germinating teliospores of the smut fungus Sphacelotheca polygoni-serrulati. SPB development in prophase I and duplication in interphase I were studied in detail. During prophase, the globular elements of the biglobular SPB enlarged, became oblate in form, developed internal layering, and became associated with astral microtubules. The middle piece decreased in size and finally disappeared. Prior to metaphase I, the two oblate elements moved apart along the intact surface of the nuclear envelope, and the nuclear membrane bulged into the space between the two SPBs. Metaphase I – early telophase I and metaphase II – early telophase II SPBs were intranuclear, oblate spheroidal in shape, and traversed by an electron-dense disc. In interphase I, an electron-dense bar appeared in association with the nuclear side of the original SPB. The bar initially overlapped one edge of the electron-dense disc and later appeared at the side of the disc. The bar became one of the metaphase II SPBs. Similarities and differences between meiosis and SPBs in Sphacelotheca polygoni-serrulati, Ustilago maydis, Ustilago esculenta, Tilletia foetida, and other heterobasidiomycetes are discussed. Key words: heterobasidiomycetes, Ustilaginales, Sphacelotheca, meiosis, spindle pole body, ultrastructure.