THE DEVELOPMENT OF THE ALEURONE LAYER IN CANOLA (BRASSICA-NAPUS)

The presence of the aleurone layer in developing seeds of Brassica napus becomes apparent about 22 days after pollination when examined with light and electron microscopic techniques. Prior to aleurone differentiation, the endosperm cellularizes centripetally to form characteristic columns of cells. The pigmented cell layer of the inner integument, which is present in dark-hulled seeds of Brassica, is just external to the aleurone. The first characteristic structures that become apparent inside the aleurone are spherosomes formed by die coalescence of small oil droplets. Shortly thereafter, the cell walls of the aleurone become markedly thickened relative to the surrounding cells. The aleurone cells of mature seeds contain lipid and protein reserves but lack starch. Development of the aleurone layer occurs first near the adaxial area and proceeds until the micropylar area finally differentiates. Endosperm chloroplasts have a characteristic lens shape when viewed in section with the electron microscope. They appear to congregate around a nucleus along with a small amount of cytoplasm causing an astroid-shaped aggregation of cytoplasm in the majority of endosperm cells but only transiently in the aleurone. DNA fluorometry and image analysis showed that aleurone nuclei are triploid; therefore the aleurone layer is derived from the endosperm.