Fine structure of spore degeneration in Podospora arizonensis

Abstract

Eight apparently equal uninucleate ascospores are delimited in the asci of the apomictic fungus Podospora arizonensis (Griff.) Cain. Four mature normally and four abort. In the normal spores the primary wall layer develops between the two delimiting membranes of the newly formed spore. The secondary and tertiary wall layers develop within the matrix of the thickening primary layer. A secondary appendage is formed at the apex and base of each normal spore. In the aborting spores wall formation ceases during secondary wall development, a tertiary wall and secondary appendages never form and the original delimiting membranes become discontinuous and reduced. In normal spores increase in lipid occurs later than in aborting spores but lipid continues to be deposited throughout development; endoplasmic reticulum, ribosomes and glycogen also accumulate. In aborting spores an early, sudden and final deposition of lipid is characteristic; endoplasmic reticulum, ribosomes and most of the glycogen disappear ; electron-dense, rod-like structures are found probably associated with membrane breakdown and, at a later stage, the mitochondria become occluded and disappear. The four aborted spores are almost empty and very small in comparison with the four mature spores.