Morphology and ontogeny of microbodies in the oomycete fungus Sapromyces elongatus

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Abstract
Ultrastructural observations on microbodies in hyphae and sporangia of the oomycete fungus Sapromyces elongatus reveal that they consistently develop adjacent to cisternae of endoplasmic reticulum. At maturity they contain a crystalline structure, having a tetragonal lattice with asymmetric spacings of 12 and 13 nm and also several small irregular tubular structures. Mature microbodies also develop numerous villous invaginations, each filled with a cistema of endoplasmic reticulum, the membrane of which is constantly spaced from, and possibly cross bridged to, the microbody membrane. Although microbodies may be appressed to mitochondria, they do not show any associations with lipid droplets. In apparent senescence the crystals remain, but the microbody membrane enlarges greatly with accompanying loss of associated endoplasmic reticulum and dilution of matrix, so that the last recognizable stage is a crystal-containing vacuole. Zoospores contain numerous mature, invaginated microbodies associated with cisternae of endoplasmic reticulum; they are clustered predominantly around the nucleus. The morphology of the microbodies and their possession of crystalline inclusions differ from previously reported oomycete microbodies and may have taxonomic value, whereas the postulated ontogenic sequence and fate of the microbodies are previously unreported and may represent a general mechanism for microbody breakdown.