Development of endosperm in Arabidopsis thaliana

The process of endosperm development in Arabidopsis was studied using immun ohistochemistry of tubulin/microtubules coupled with light and confocal las er scanning microscopy. Arabidopsis undergoes the nuclear type of developme nt in which the primary endosperm nucleus resulting from double fertilizati on divides repeatedly without cytokinesis resulting in st syncytium lining the central cell. Development occurs as waves originating in the micropylar chamber and moving through the central chamber toward the chalazal tip. Pr ior to cellularization, the syncytium is organized into nuclear cytoplasmic domains (NCDs) defined by nuclear-based radial systems of microtubules. Th e NCDs become polarized in axes perpendicular to the central cell wall, and anticlinal walls deposited among adjacent NCDs compartmentalize the syncyt ium into open-ended alveoli overtopped by a crown of syncytial cytoplasm. C ontinued centripetal growth of the anticlinal walls is guided by adventitio us phragmoplasts that form at interfaces of microtubules emanating from adj acent interphase nuclei. Polarity of the elongating alveoli is reflected in a subsequent wave of periclinal divisions that cuts off a peripheral layer of cells and displaces the alveoli centripetally into the central vacuole. This pattern of development via alveolation appears to be highly conserved ; it is characteristic of nuclear endosperm development in angiosperms and is similar to ancient patterns of gametophyte development in gymnosperms.