Ovulate cone, pollination drop, and pollen capture in Sequoiadendron (Taxodiaceae)

Abstract

In Sequoiadendron ovules are borne inside the ovulate cone, and pollination drops secreted from these ovules collect pollen. We examined: (I) the relation between ovular position and pollen capture; (2) pollen behavior when in contact with a pollination drop; and (3) ultrastructure of ovules during pollination drop secretion. During wet periods a water sheet forms on the surface of the cone due to bract shape and wettability. Pollination drops persist inside the wetted cone, and pollen capture resumes immediately after drying. Pollen landing on a pollination drop is taken inside the drop and carried into the micropyle when the drop contracts. Several notable ultrastructural features appear in the nucellus, integument, chalaza, and bract lamina during pollination-drop secretion. The abaxial surface of the lamina is covered by a membrane that may contribute to the wettable nature of the surface.

The Pollination of Mid Mesozoic Seed Plants and the Early History of Long-proboscid Insects1,2,3

“…The ancestral pollination mode in seed plants is wind pollination, wherein the distal part of an ovule bore a short, tubular micropyle that became filled with secretory fluids originating from vacuoleladen, secretory tissue adjacent to the nucellus. Secreted pollination fluid fills the micropylar tube, forming a bubble, or drop, at the terminus to trap ambient pollen (Chesnoy, 1993;Takaso & Owens, 1996). This is followed by fluid resorption or evaporation and withdrawal of the drop with trapped pollen to the nucellus where fertilization occurs through a pollen tube (Gelbart & von Aderkas, 2002).…”

Generalist flowers and phytophagous beetles in two tropical canopy trees: resources for multitudes

“…This mechanism occurred in Late Pennsylvanian seed ferns such as Calliospermarion pusillum (Rothwell, 1977), found as a permineralized substance containing pollen grains within a micropyle in (B) (abbreviations: n, nucellus; s, sclerotesta; p, pollination drop), magnified in (C). Pollination drops are illustrated for Sequoiadendron giganteum (Pinopsida: Cupressaceae) in (D) abbreviation: mp, micropyle) (Takaso & Owens, 1996); Phyllocladus glaucas (Pinopsida: Podocarpaceae) in (E) (abbreviation: c, ovulate cone) (Tomlinson & al., 1997); Ginkgo biloba (Ginkgoopsida: Ginkgoaceae) in (F); Taxus baccata (Pinopsida: Taxaceae) in (G) (Proctor & al., 1996); an unidentified species of Ephedra (Gnetopsida: Ephedraceae) in (H) (Gifford & Foster, 1989); Zamia pumila (Cycadopsida: Zamiaceae) in (I) (Tang, 1995); and Welwitschia mirabilis (Gnetopsida: Welwitschiaceae) in (J) (Gifford & Foster, 1989). .…”

Stockeystrobusgen. nov. (Cupressaceae), and the evolutionary diversification of sequoioid conifer seed cones

“…A similar pollination mechanism appears to characterize Saxegothaea conspicua Lindley (Tison 1908;Chamberlain 1935), but it is unclear whether the post-pollination nucellus displays a highly convoluted apical region. Although the structure of the pollen chamber has been characterized for several species of both living and extinct Cupressaceae e.g., Arnoldi 1900; Takaso and Owens 1996;Owens et al 1998;Tomlinson 2012;Spencer et al 2015), Stockeystrobus digitata is the first species of the family in which this character has been found. This feature could be interpreted as either a strong indication that a specialized pollination mechanism like those of Araucariaceae and Saxegothaea (Tison 1908;Owens et al 1998) also was characteristic of some Cretaceous species of the subfamily Sequoioideae, or that it is plesiomorphic among the (Sciadopityaceae + Cupressaceae) + (Araucariaceae + Podocarpaceae) clade (Leslie et al 2012) as a whole.…”