Arnold, Carl-Gerold

Brand, Norbert

In order to elucidate the mitochondrial arrangement in the mature zygote of the green alga Chlamydomonas rein-hardii conventional chemical fixation is compared with freeze-substitution fixation. It is shown that in spite of different pretreatments for increased permeabi1 itiy of the thick and isolating cell-wall and for preventing normal cell-wall formation, chemical fixation still acts too slowly to stabilize the mitochondrial structures in their true-to-life state to be suitable for morphometric investigation. On the contrary cryofixation and subsequent cryosubstitution provide convincing quality of fixation of the whole cell. For the first time, excellent preservation of mitochondrial structures in the zygote could be observed. Methodological requirements and cellular features are reported and discussed as well as the average yield of well frozen-substituted zygotes. Besides the advantages in structural preservation also some peculiarities and factors limiting successful freeze-substitut ion fixation of thick-walled green plant cells can be pointed out on this organism.

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