| Abstract: | Cultures of Tetrahymena pyriformis were grown with and without the addition of Fe and with no aeration. The same cultures were used both for determinations of the cellular Fe and Ca concentrations and the exchange of Ca (reported earlier), and for the ultrastructural study. In all cultures there was an increase in rounded, tubuli-deficient mitochondria at the transition to the prestationary growth phase. In the non-aerated culture (high cellular Fe content) these changes were less marked. In the Fe-deficient culture, however, these mitochondrial changes were seen as early as the late exponential growth phase, and tubuli-degeneration then increased during the prestationary growth phase. In this culture an irregular infolding of the outer mitochondrial membranes occurred. These changes are discussed in correlation with cytochromes, Fe-dependent desaturation of fatty acids, and high Ca concentration (non-aerated cells). During the prestationary growth phase of the non-aerated culture there was a marked increase in the amount of mitochondrial tubuli. In the organelles identified as peroxisomes there was, in all the cultures, an increased granular density of the matrix at the transition to the prestationary growth phase (in the Fe-deficient cells this occurred in the late exponential growth phase). This was correlated with an increased peroxisomal activity. The Fe-deficient culture has cells with very irregularly formed peroxisomes. This organelle was in all the cell-material very sensitive to the method of fixation. In the Fe-deficient late exponential cells there are long, bifacial pieces of RER (one side rough and the other smooth) which later undergo degradation. Many lipid droplets were seen at the ends of RER. Structures which in the literature have been called 'ergoplasm-like stacks of flattened rough cisternae' were found in the non-aerated exponential cells. They were absent from prestationary cells. In all the cultures there was an increased aggregation of the ribosomes in the cytoplasm during the prestationary growth phase. This was correlated with the accumulation of Ca in this cell fraction. An explanation is suggested regarding the earlier reported variations in the exchange of Ca, found in all the types of cultures at the transition to the prestationary growth phase. |
