Formation et évolution des ascospores de Tuber melanosporum (truffe noire du Périgord, Discomycètes)

Abstract

In Tuber melanosporum, as in a few other truffles (genus Tuber), ultrastructural observations show that each ascospore is delimited in the ascus apical zone through an individual process, the single primordial wall originating from a lomasomic extension. The primordial wall splits into two layers (primary wall), then a secondary part is deposited. At the most complex stage it comprises, from interior to exterior: a regular clear epispore; a dark exospore producing ornamental spines; a clear perispore which strongly dilates then shrinks around each spine; a limiting ectospore. In the mature ascospore, the ascospore wall is composed of only two superimposed parts corresponding to the two ascospore walls visible with light microscope. The clear internal part is the epispore and the brown echinulate external one represents the joined exospore, perispore, and ectospore. The ascospores contain six to eight early formed nuclei and cytoplasmic inclusions. Mitochondria prevail in young ascospores whereas oil droplets nearly fill the mature ones.