Ultrastructural and Light Microscopic Localization of Carbohydrates and Peroxidase/Catalases in Lagenidium Giganteum Zoospores

ABSTRACT

Zoospores of the oomycete Lagenidium giganteum specifically recognize and then encyst upon mosquito larvae. As a step towards understanding the basis for this specific recognition, we examined the ultrastructure and cytochemistry of the zoospores. Zoospore shape and organellar arrangement are similar in L. giganteum and other secondary-type oomycete zoospores. The ultrastructure of zoospores of L. giganteum differs from other Oomycetes mainly in details of vesicle morphology and mitochondrial arrangement. In our studies, we emphasized the outer surface of the zoospores where recognition molecules are likely to be present. Using silver methenamine and thiosemicarbazide-silver proteinate stain sequences, carbohydrate was found at the plasma membrane of zoospores. Ferritin- and fluorescein-labelled concanavalin A binding patterns indicated α-D-mannosyl and/or α-D-glucosyl residues are exposed on the outer surface of the plasma membrane of the zoospore and the wall of the cyst. Within the zoospores, the membranes of small peripheral vesicles, and the membranes and contents of golgi apparati and peripheral cisternae showed evidence of carbohydrate content with silver staining. We did not find clear evidence of carbohydrates among the contents of the large and small peripheral vesicles. Zoospores treated with diaminobenzidine to visualize peroxidases and catalases exhibited increased light and electron opacity in their mitochondria, as well as a fuzzy coat on the external surfaces of their plasma membranes.

Key Words:

• cytochemistry
• Lagenidiales
• Lagenidium giganteum
• Oomycetes
• ultrastructure
• zoospore