Melanization of verticillium dahliae at the cellular level, 1982

Abstract

Microsclerotia are thick-walled, large globose cells which serve as survival structures in Verticillium dahliae. The globose cells are characteristic of older hyphal regions. The wild-type strain produces melanin which can be observed within and on the wall of the microsclerotia and extracellular fibers. Fungal melanin is considered necessary for the survival of microsclerotia during long periods of unfavorable conditions. In order to examine the formation of microsclerotia as related to melanin production in wild-type (t-9), the albino-1 microsclerotia (alm-1) and the brown-1 microsclero�tia (brm-1) mutants were grown on potato dextrose agar (PDA) over-laid with cellophane or polygalacturonic acid medium (PGAM) which induces synchronous development of microsclerotia. Albino-1 was induced to produce melanin by a brown substance (scytalone) in the culture filtrate of brm-1 mutant. Scytalone-induced albino (s-alm-1) was compared cytologically with the development of melanin in t-9. Observations were made by phase contrast and trans-mission electron microscopy. The cellular changes that accompanied the change of alm-1 to s-alm-1 were frequently observed mitochondria along with single and double membrane vesicles. There were electron-dense melanin granules similar to t-9 observed within extracellular fibers and on the wall of micro- sclerotia. The precipitate from the 3,3'-diaminobenzidine reaction was demonstrated on the inner mitochondrial mem�brane of alm-1, while s-alm-1 showed activity on the inner and outer mitochondrial membranes. The above mentioned changes in organellar structures and arrangement suggest a correlation with the production of melanin as seen in the wild type