TRANSMISSION ELECTRON-MICROSCOPY OF X-RAY-IRRADIATED TELIOSPORES OF USTILAGO-MAYDIS

Teliospores of Ustilago maydis (De Candolle) Corda were irradiated wit h CuK alpha X-ray with a BRON UM1 instrument at 35 KV, 20 mA and the r esulting thin sections investigated with a TEM. The length of time of irradiation was 5 s, 15 s, 35 s, 60 s, and 300 s. The wall of the teli ospore, which contains melanin, is extremely resistant, but increases in the radiation dose resulted in ultrastructural alterations. The end ospore became swollen, the protoplasm contracted and the epispore disi ntegrated. The degradation of the electron dense particles in the exos pore is obvious after ct relatively short time of irradiation. The X-r ay effect explored the molecular structure of the wall. In highly magn ified pictures several kinds of molecular systems were observed, inclu ding chain molecules and cyclic derivates among the other constituents of the melanin molecules.