title: Starch-accumulating (S-type) sieve-element plastids in Hydatellaceae: implications for plastid evolution in flowering plants.
abstract: TEM investigation of sieve-element plastids in three species of Trithuria, the sole genus of the small aquatic family Hydatellaceae, show that P-type plastids are absent from this genus and only starch-accumulating (S-type) sieve-element plastids are present. This discovery is consistent with the recent transfer of Hydatellaceae from the highly derived monocot order Poales (grasses and their allies) to the early-divergent angiosperm order Nymphaeales (waterlilies) based on molecular phylogenetic data. Species of Poales consistently possess P2-subtype plastids, in common with other monocots, but only S-type plastids are present in Nymphaeales. The results confirm that Hydatellaceae do not belong in monocots. Optimisation of the two major types of sieve-element plastid onto a recent phylogeny of early-divergent angiosperms confirms that S-type is the primitive form and indicates that P-type sieve-element plastids have evolved more than once in angiosperms.
authors: Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey, UK.
authors: Julia
authors: J
authors: Tratt
authors: Christina J
authors: CJ
authors: Prychid
authors: H-Dietmar
authors: HD
authors: Behnke
authors: Paula J
authors: PJ
authors: Rudall
mesh_terms: D019684:Magnoliopsida; D010802:Phylogeny; D018087:Plastids / Q000235:genetics*; D013213:Starch
chemical_list: D013213:Starch