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Yehoshua Saranga and Jules Janick

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Christiane Cabral Velho, Yehoshua Saranga and Jules Janick

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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Les Frey, Yehoshua Saranga and Jules Janick

Somatic embryogenesis was induced from internodal callus of `Scania', `Improved White Sim', and `Sandra' carnation (Dianthus caryophyllus L.). The optimum protocol for the induction of somatic embryogenesis included initiation of callus in liquid basal Murashige and Skoog medium supplemented with 3.0 μm 2,4-D followed by transfer to liquid basal medium lacking 2,4-D for embryo development. Somatic embryos originated from single cells and early embryonic development proceeded conventionally (i.e., via globular, heart-shaped, and torpedo stages), but clearly developed apical or root meristems were not always formed. A few embryos developed into seedlings and were acclimatized to ex vitro conditions. Chemical name used: 2,4-dichlorophenoxyacetic acid (2,4-D).

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Yehoshua Saranga, David Rhodes and Jules Janick

Desiccation tolerance of somatic embryos is a key factor for production of dry synthetic seeds. In celery (Apium graveolens L.) desiccation tolerance can be enhanced by optimization of culture duration, ABA application, or sucrose concentration in the embryo production medium. Morphologically mature embryos cultured for 10 days have shown higher desiccation tolerance then those cultured for 8 days, indicating that biochemical changes occur without any noticeable morphological changes. Application of ABA (1 μM) for the last two days of the embryo production cycle was critical for inducing desiccation tolerance; ABA application for the last four days had some additional beneficial effect. Desiccation tolerance was further enhanced by increasing the sucrose concentration of the embryo production media from 3% to 7% for the last two days. Increased desiccation tolerance achieved with optimal harvest timing and ABA application were associated with increased endogenous proline and aminobutyrate, and reduced glutamine.

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Yehoshua Saranga, David Rhodes and Jules Janick

Tolerance to partial desiccation and amino acid composition of celery (Apium graveolens L. cv. SB 12) somatic embryos were investigated under various culture durations and with exogenous application of 1 μm ABA, proline, and/or γ -aminobutyrate (GABA). ABA consistently increased tolerance to partial desiccation and elevated proline and GABA content of embryos. The changes in tolerance to partial desiccation associated with changes in culture duration (optimum 9 to 10 days) correlated with embryo proline content. Exogenous proline increased embryo proline content and tolerance to partial desiccation. Exogenous GABA increased embryo GABA content and tolerance to partial desiccation only when applied in combination with proline. Chemical name used: abscisic acid (ABA).

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Yehoshua Saranga, Y.-H. Kim and Jules Janick

Effects of reduced osmotic potential on somatic embryos of celery (Apium graveolens L.) were studied in an attempt to understand and improve their tolerance to partial desiccation. Embryos responded similarly to application of high osmoticum (384 mOs/kg H2O vs. 190 mOs/kg H2O in the control), achieved either by manipulation of sucrose or polyethylene glycol concentrations (PEG). Treatments of high osmotic concentration applied during the last 2 days of the embryo production cycle increased embryo survival and conversion after partial desiccation. The most striking effect of the high osmotic concentrations was the 4-fold increase in proline, while a 2-fold increase was obtained with 1 μm ABA alone. Application of high osmotica decreased reducing sugars, increased sucrose, but did not affect starch content of embryos; of these responses, only the change in sucrose was similar to that induced by ABA. Osmotic treatments did not affect total fatty acid content in the embryos compared to the 2-fold increase induced by ABA. Chemical name used: abscisic acid (ABA).

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Yehoshua Saranga, Avishag Levi, Pavel Horcicka and Shmuel Wolf

The cause for the differences in germination ability of large and small confection sunflower (Helianthus annuus L.) seeds was investigated over 3 years. The source-sink relationship was manipulated to better explore the differences between seeds of various sizes and to study the role of the embryo and the pericarp (hull) in controlling germination ability. Percent germination of large seeds was significantly lower than that of small seeds when tests were performed at 15 °C. Increasing the ratio of leaf area to number of developing seeds caused an increase in mean seed mass, but resulted in a lower percentage of germination. Seed vigor, as measured by mean time to germination or to emergence of hulled seeds or by rate of root elongation, was negatively correlated with embryo mass, indicating that the low vigor of large seeds is not due to the mechanical barrier imposed by the hull. Analysis of electrolyte leakage confirmed the hypothesis that the low quality of large seeds results from a disturbance during the process of seed development.