ADHESION-REDUCED MUTANTS AND THE WILD-TYPE NECTRIA-HAEMATOCOCCA - AN ULTRASTRUCTURAL COMPARISON OF THE MACROCONIDIAL WALLS

We examined the macroconidial wall layers of various strains ofNectria haematococca prior to germ tube emergence. Using freeze-substituted cells, the wall ultrastructure of an adhesion-competent wild-type strain was compared with two adhesion-reduced mutants, LE1 and LE2. At 0 h, the freshly harvested macroconidia of all strains had a similar, bilayered wall and were all nonadhesive. After 1 h, wild-type macroconidia were adhesive and their cell walls exhibited two additional layers not present at 0 h: a pellicular third layer and a thick, outermost fourth layer. Material from the fourth layer was apparently discharged into the surrounding medium. In contrast to the wild type, the mutants after 1 h were adhesion-deficient; the outermost wall layers of LE1 and LE2 differed from each other and from the wild type. There were also differences in the wall layers and extracellular matrices between the mutants and the wild type after 3- and 5-h incubations. Plasma membrane invaginations were not observed at 0 h, but were detected in both wild type and mutant macroconidia at 1, 3, and 5 h. The data demonstrate that in macroconidia ofN. haematococca (1) the wall and associated extracellular matrix undergo major morphological changes prior to germ tube emergence and (2) development of adhesiveness is correlated with the appearance of new wall layers. © 1991 Academic Press, Inc.