The secretion of phenolic compounds following fertilization in Acrocarpia paniculata (Fucales, Phaeophyta)

We have used light and electron microscopy to study the secretion of phenolic substances by zygotes of the brown alga Acrocarpia paniculata (Turner) Areschoug. Phenolic compounds, packaged within vesicles known as physodes, are a major cytoplasmic component of eggs and zygotes of Acrocarpia paniculata. Physodes accumulate at the egg periphery, and were identified using several different histochemical stains. Immediately after fertilization, zygotes secrete large numbers of phenolic bodies. The magnitude of phenolic release is so great that the zygote membrane is distorted during this process. However, we have found no cytologic evidence for endocytosis. The secreted phenolics surround the zygote and appear to impair sperm motility by causing sperm to slow down and become motionless. As the zygote wall is secreted, the phenolics form part of the developing wall, becoming oxidized and brown in color. We conclude that phenolics play an important role in the early developmental processes of A. paniculata, and we discuss their possible functional significance.