Embryo development, megagametophyte storage product accumulation, and seed efficiency in Taxus brevifolia

Abstract

Taxus brevifolia Nutt. has a reduced ovulate structure that consists of a single ovule in a leaf axil instead of a compound ovulate strobilus. Taxus brevifolia on southern Vancouver Island, British Columbia, were studied over three seasons. Proembryos occurred from mid-May to mid-June. They underwent four free nuclear divisions forming 16 nuclei before cellularization. Early embryos were present from mid-May to mid-August. Simple polyembryony was observed up to the massive embryo stage, and differential growth of the embryonal cells was interpreted as incomplete cleavage polyembryony. Mid-embryos were present from mid-June to late August and had a distinct protoderm and focal zone. Late embryos were visible from mid-July onwards. Carbohydrates began accumulating at the early embryo stage, whereas proteins and lipids accumulated in the late embryo stage. The presence of a red aril corresponded to increased amounts of lipid in the megagametophyte cells. Individual seeds matured from July until November. The seed efficiency ranged from 0 to 16% and averaged 5%. Prezygotic loss was the most common fate of ovules, followed by postzygotic loss. Possible causes of this poor seed efficiency are poor pollination success, insect damage, or light limitation.

Oviposition strategies of conifer seed chalcids in relation to host phenology

“…Following embryo formation ( Fig. 4a-P/E), the female gametophyte tissue stores starch, lipid, and protein (Krasowski and Owens 1993;Anderson and Owens 2001;Chiwocha and von Aderkas 2002).…”

Variant maturity in seed structures of Pinus albicaulis (Engelm.) and Pinus sibirica (Du Tour): key to a soil seed bank, unusual among conifers?

“…The amount of lipids may, however, be difficult to visualize reliably using LM, because the embedding process tends to dissolve lipids. The amount of stained lipids in the megagametophyte is reported to increase simultaneously with chemical maturation of the surface structures (Anderson and Owens 2001). Whitebark pine seeds are reported to comprise 52% lipids by dry weight, and Siberian stone pine seeds 51-75% (Lanner and Gilbert 1994 and references therein).…”

Pollen limitation and fruit abortion in a declining rare tree, the Eurasian yew (Taxus baccataL.): A reproductive cost of ecological marginality

“…This implies that treated branches had a greater number of carbohydrate sinks during fruit growth, though this difference did not increase abortion rates in treated branches (Lee 1988;Anderson & Owens 2001). This fact indicates that fruits growing in treated branches (bearing more fruits) experienced similar withinbranch competition for resources than fruits in less productive control branches.…”