ULTRASTRUCTURE OF CONIDIA AND THE CONIDIUM AGING PROCESS IN THE PLANT-PATHOGENIC FUNGUS COLLETOTRICHUM-GRAMINICOLA

The influence of age on conidial ultrastructure was investigated in Co lletotrichum graminicola. The cytoplasmic volume of young conidia-thos e harvested from 5-7-d-old cultures-was dominated by lipid bodies. The se conidia also were characterized by numerous small vacuoles with ele ctron-dense contents. Other structures present included mitochondria, microbodies, ribosomes, elements of tubular ER, short strands of rough ER, multivesicular bodies, simple cisternal elements, Woronin bodies, microtubules, and large amounts of what appeared to be glycogen. Olde r conidia harvested from 30-35-d-old cultures exhibited a significantl y different ultrastructure. They contained fewer lipid bodies, lacked the large glycogen deposits, were very highly vacuolate, and contained sheetlike strands of ER and extensive aggregations of tubular ER. Str uctures thought to be autophagic vacuoles also were present. The conid ial wall appeared similar in conidia of both ages and consisted of a t hicker inner electron-transparent layer and a very thin outer layer co mposed of fine electron-dense fibers. The inner layer stained moderate ly for polysaccharides and could be labeled with wheat germ agglutinin -gold complexes indicating the presence of chitin. The outer layer sta ined intensely for polysaccharides but did not label with wheat germ a gglutinin. The outer surface of the conidium could be labeled with alp ha-amylase-gold complexes specific for a-1,4 glucans. The observed cha nges in ultrastructure may serve as indicators of physiological change s that affect the ability of the fungus to survive.