SUMMARY: Structural changes in mitochondria and other spore constituents during maturation and germination of conidia were investigated. During maturation there was an increase in spore volume and number of mitochondria, while endoplasmic reticulum and electron-dense bodies disappeared. The stellate, precursor-lipid-granules underwent structural and chemical changes, the smooth plasmalemma invaginated and the conidial wall became thicker and relatively impermeable. The resting conidium contained few internal structures - only a single nucleus, several ovoid mitochondria and a few lipid granules.

After inoculation in germination medium there was a 4 h lag period, during which the conidia did not increase significantly in size, take up cotton blue or undergo a change in mitochondrial number. However, metabolic activity was evident from the reappearance of the electron-dense bodies, a change in the shape of some of the mitochondria and an increased permeability to the various fixation and embedding reagents.

The period of conidium swelling was accompanied by a reappearance of the endoplasmic reticulum, often in association with and seemingly interconnecting the various organelles. The lipid granules gradually disappeared and the electron-dense bodies became partially evacuated. Mitochondria increased in number, many having cup-shaped configuration; an unbalanced growth of surface membranes with respect to matrix may have been the physical cause for this shape. The nucleus divided at least once before the emergence of the germ tube. Structural changes continued during germ-tube emergence. The mother conidium in Trichoderma retained its ultrastructural integrity, and did not vacuolate.


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