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

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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 1 × 105 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.Key words: secondary conidia, lipid bodies, vacuoles, confocal microscopy, Colletotrichum.

Colletotrichum acutatum peut former une ou plusieurs conidies secondaires après la germination conidiale et avant la croissance mycéliale. La formation des conidies secondaires et la germination étaient influencées par la concentration de conidies. Des concentrations plus élevées que 1 × 105 conidies/mL étaient associées à une diminution de la germination et à l'émergence de conidies secondaires. Les conidies secondaires peuvent se former soit seules ou simultanément à la formation des tubes germinatifs et aux appressoria. L'analyse confocale a montré la présence de plusieurs inclusions lipidiques emmagasinées à l'intérieur de conidies non germées dont le nombre diminuait lors de la formation du tube germinatif et des appressoria, avec ou sans formation de conidies secondaires. Cette diminution survenait aussi lors de la formation des conidies secondaires seules. Alors qu'il y avait une diminution à l'intérieur des conidies germées, les inclusions lipidiques apparaissaient à l'intérieur des conidies secondaires depuis les phases initiales. Une vacuolisation intense à l'intérieur des conidies primaires germées survenait au moment de la diminution des inclusions lipidiques, celles-ci étant internalisées et digérées par les vacuoles. Durant ces événements, de petites vésicules acides se formaient à l'intérieur des conidies secondaires. Considérant le fait que les conidies étaient maintenues dans l'eau distillée sans nutriments exogènes, il est clair que les conidies non germées contiennent des réserves de lipides suffisantes à la formation des tubes germinatifs, des appressoria, les conidies secondaires renflouant ces réserves lipidiques. Ces résultats suggèrent qu'une régulation complexe et bien balancée rend possible l'activation des sentiers cataboliques et anaboliques de ces inclusions lipidiques.Mots clés : conidies secondaires, inclusions lipidiques, vacuoles, microscopie confocale, Colletotrichum.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: February 1, 2006

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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