STRUCTURAL-ANALYSIS OF EMBRYOGENESIS AND ENDOSPERM FORMATION IN CELERY-LEAFED BUTTERCUP (RANUNCULUS-SCELERATUS L.)

Embryo and endosperm development were studied in celery-leafed butterc up (Ranunculus sceleratus L.) by light and electron microscopy. The fi rst pollen tubes entered embryo sacs within 8 h after pollination. The two first divisions of the zygote were transversal and the three-cell ed pro-embryo was linear. Its basal cell gave rise to a multicellular suspensor with the hypophysis, and its middle and upper cell formed th e embryo proper. Because of this pattern of cell division, the embryog enic pattern of R. sceleratus differs from the Onagrad Type to which R anunculus supposedly belongs. The suspensor showed limited growth and similarly the embryo proper remained in the early torpedo stage in the mature seed. Endosperm was nuclear initially. Cellularization was pre ceded by alveolation and coincided with the accumulation of storage pr oducts in lipid droplets and amyloplasts, Starch grains gradually disa ppeared whereas protein bodies and lipid droplets accumulated during f urther development. At maturity, the endosperm occupied the greater pa rt of the seed and its cytological features varied around the embryo. The endosperm cells surrounding the embryo suspensor persisted whereas those surrounding the embryo proper degenerated. The site-specific de generation occurred after the establishment of the protoderm and point s to the interaction between embryo proper and endosperm. 'Multivesicu lar structures' were observed in the endosperm at the alveolation stag e. They may be involved in the transport of metabolites between the ap oplast and symplast.