Morphology and lipid body and vacuole dynamics during secondary conidia formation in Colletotrichum acutatum: laser scanning confocal analysis

Colletotrichum acutatum may develop one or more secondary conidia after conidial germination and before mycelial growth. Secondary conidia formation and germination were influenced by conidia concentration. Concentrations greater than 1x105 conidia/mL were associated with germination decrease and with secondary conidia emergence. Secondary conidia can form either alone or simultaneously with germ tubes and appressoria. Confocal analysis showed numerous lipid bodies stored inside ungerminated conidia, which diminished during germ tube and appressoria formation, with or without secondary conidia formation. They were also reduced during secondary conidia formation alone. While there was a decrease inside germinated conidia, lipid bodies appeared inside secondary conidia since the initial stages. Intense vacuolization inside primary germinated conidia occurred at the same time as the decrease in lipid bodies, which were internalized and digested by vacuoles. During these events, small acidic vesicles inside secondary conidia were formed. Considering that the conidia were maintained in distilled water, with no exogenous nutrients, it is clear that ungerminated conidia contain enough stored lipids to form germ tubes, appressoria, and the additional secondary conidia replete with lipid reserves. These results suggested a very complex and well-balanced regulation that makes possible the catabolic and anabolic pathways of these lipid bodies.