Quantitative Ultrastructural Investigations of the Life Cycle of Trypanosoma brucei: A Morphometric Analysis*

SYNOPSIS. The quantitative ultrastructure of the developmental stages of Trypanosoma brucei brucei in its vector Glossina morsitans was studied by morphometric analysis. Values from ectoperitrophic midgut forms, proventricular forms, epimastigote and metacyclic forms in the salivary gland are compared with results from bloodstream forms, published previously. Significant differences in the volume densities of the trypanosome's single mitochondrion, of microbody-like organelles and in the surface densities of inner and outer mitochondrial membranes were found throughout the whole life cycle. A great increase in volume density of the mitochondrion was observed after transfer to the insect host; reduction took place during metacyclic development. Parallel to the biogenesis of the mitochondrion a reduction of microbodies was found in proventricular forms and there was a great increase in metacyclic forms concomitant with the regression of the mitochondrion. Metacyclic forms had a close quantitative morphologic similarity to bloodstream forms. The results are discussed in connection with changes in structure and in oxidative metabolism.