Zygotic dormancy underlies prolonged seed development inFranklinia alatamaha(Theaceae): a most unusual case of reproductive phenology in angiosperms

Abstract

In Franklinia alatamaha (Theaceae) an extended period of dormancy, associated with winter, separates pollination in the late summer and autumn from observable fruit growth, which occurs during the subsequent summer season. Here, ovule and early seed development were examined to decipher the timing of reproductive events that underlie this unusual phenological pattern. Female gametophytes were found to be mature before pollination. Evidence for double fertilization was observed soon after pollination. Early endosperm development progresses for up to 3 months after fertilization but comes to a standstill at the onset of winter. The zygote becomes dormant shortly after fertilization and does not divide during the autumn or winter. At the start of the following growing season, endosperm development is reinitiated and the first events associated with the formation of an embryo occur. Seed development is completed roughly at the same time as new flowers are opening, a full year after pollination and fertilization. Dehiscence of fruits does not occur until later in autumn. The prolonged zygotic dormancy in Franklinia is exceedingly rare among angiosperms and differs markedly from patterns of delayed fertilization that typically underlie extended periods between pollination and seed maturation in other temperate, perennial species.

Prolonged embryogenesis in Austrobaileya scandens (Austrobaileyaceae): its ecological and evolutionary significance

“…In various species of Trithuria, germination occurs within a matter of weeks after seeds are sown (Tuckett et al, 2010;Friedman et al, 2012). Compared with other taxa, the nearly year-long period required for germination in A. scandens is extreme by most measures (Schoonderwoerd & Friedman, 2016). The uniquely large and slow-to-germinate seeds of Austrobaileya are apomorphic within Austrobaileyales (Table 1).…”