Characteristics of Extracellular Adhesions Produced During Saprolegnia Ferax Secondary Zoospore Encystment and Cystospore Germination

ABSTRACT

Fluorescence microscopy of lectin binding and electron microscopy of surface features were used in an investigation of adhesion characteristics of germinating secondary cystospores of Saprolegnia ferax. Adhesive material at two locations bound S. ferax germlings to glass coverslips or to boiled onion epidermis. As secondary cystospores germinated, they released along the germ tube extracellular adhesive material to which fluorescently labeled wheat germ agglutinin bound. Similarly, this lectin also bound to portions of the adhesion pad between the secondary cystospore and its substrate. Scanning electron microscopy revealed that although material of the adhesion pad extended a short distance along the germ tube, the material at the germ tube tip was not continuous with this previously released adhesive material. Changes in the structure of the adhesion pad material indicated that it had fluidity when first released, but later its fluidity became constrained, possibly by progressive polymerization. Evidence suggests that adhesives found along the germ tube were released at the tip during elongation. The site of germ tube initiation appeared dependent on more cues than mere prealignment of the cystospore when a secondary zoospore adhered to a substrate along its ventral surface. It is concluded that S. ferax is well adapted to its aquatic environment because both secondary cystospores and colonizing germ tubes attached to substrates with adhesives.

Key Words:

• adhesion
• exocytosis
• K2-bodies
• lectins
• Oomycetes
• Saprolegnia
• ultrastructure