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  • Author or Editor: Christiane Cabral Velho x
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Density changes associated with developing zygotic embryos of loblolly pine (Pinus taeda L.) and somatic embryos of celery (Apium graveolens L.) were determined using sucrose gradients. Continuous sucrose gradients were used to evaluate relative density of loblolly pine embryos from July 25, when embryos could be microscopically observed, to November 7, 1988. Embryos density declined during development with a maximum (51% sucrose equivalent or 1.2331 g/ml) at first sampling and then remain relatively constant (10% sucrose equivalent or 1.0306 g/ml) after day 49. Density changes were inversely related to embryo length.

Celery somatic embryos, cultured for 6, 8, 10, or 12 days were separated with sucrose solutions varying from 9 to 16% in 1% intervals. Embryos were classified as overmature (expanded cotyledons), mature (torpedo), and immature (globular). The number of low density embryos increased from 6 to 12 days. The highest conversion to normal seedlings after desiccation for 48 hr at 90% relative humidity was obtained with overmature and mature embryos, but some immature somatic embryos also survived. Maximum conversion was obtained from embryos with density equivalent of 12% to 14% sucrose (1.0448 g/ml to 1.0531 g/ml) at days 10 and 12.

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Mature seed weight of loblolly pine (Pinus taeda L.) averaged 25 mg (dry weight), of which 55.0% was seedcoat, 38.5% megagametophyte, and 6.4% embryo. Fatty acid (FA) content (dry-weight basis) was 17.5% for whole seed, 0.4% for seedcoat, 36.2% for megagametophyte, and 51.2% for embryo. Distribution of FAs (16:0; 18:0; 18:1; 18:2; 18:3 Δ5,9,12; 18:3 Δ9,12,15; 20:0; and 20:3) differed in seedcoat, megagametophyte, and embryo, but 18:2 was the predominant FA in all tissues. Seed development was analyzed for 110 days from 25 July, the year following pollination. Embryos could be macroscopically observed on or about day 30. Embryo dry weight, length, and FA accumulation increased until about day 50 and then remained constant. Embryo density decreased from day 30 to 50 and then stabilized at ≈1.0366 g·ml-1 or 10% sucrose equivalent. Excised zygotic embryos did not germinate in vitro until after day 51; germination increased linearly after this date, reaching 80% by day 72.

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