Osmotic Measurements of Whole Ovules During Loblolly Pine Embryo Development, 1997 Biological Sciences Symposium Proceedings

The osmotic environment has been shown, both in angiosperms and gymnosperms, to play an important role in embryo development. In 1993 and 1994 the osmotic environment in ovules of loblolly pine (Pinus taedu) was measured. Cones were collected weekly from late June to October and shipped overnight on ice to IPST. Ovules were prepared for measurement by removing the seed coat, integument, and nucellus. Three to five whole ovules from a cone were placed in the osmometer sampling pan of a Wescor 5500 Vapor Pressure Osmometer modified with a cycle hold switch and allowed to equilibrate for 30 minutes. After osmotic readings were obtained, each ovule was opened and the embryo rated for developmental stage. Cones from three trees were processed during 1993 and again in 1994 providing six sets of osmotic profiles during embryo growth and development. Most cone collections showed a consistent water potential pattern: high readings of 400- 500 mmol/Kg during early embryo development in late June to early July when embryo stages 1-2 occur; a reduction for one to several weeks to levels of 200-300 mmol/Kg, correlating with stages 4-5; followed by a steady increase in osmotic level from 350 to 700-800 mmol/Kg for stages 6 onwards from late August onwards. We are actively testing whether mimicking natural changes in water potential within the tissue culture environment will promote somatic embryo development.