The developmental biology of cereal endosperm

Abstract

This chapter summarizes the current understanding of structural aspects of cereal endosperm development with emphasis on the cytoskeleton and its role in morphogenesis. The developmental pathway of nuclear-type endosperm includes unusual cell and microtubule cycles and methods of wall placement. After double fertilization, the primary endosperm nucleus divides repeatedly without cytokinesis resulting in a large syncytium that lines the periphery and surrounds the central vacuole. During interphase this "liquid" endosperm is elegantly organized into functional units termed nuclear cytoplasmic domains (NCDs) by radial microtubule systems (RMSs) emanating from the nuclei. Cellularization is driven by the RMS microtubule cycle in which hoop-like cortical microtubules and preprophase microtubule bands (PPBs) are absent. It comprises alternation of two stages: deposition of anticlinal walls without mitosis leading to formation of alveoli, and periclinal walls following mitosis in the alveoli. Following centripetal cellularization, three principal tissues are differentiated: the central endosperm in which food reserves are stored, a transfer region specialized for uptake of metabolites, and the peripheral aleurone that releases enzymes to mobilize reserves at germination. The PPB microtubule cycle typical of meristematic growth replaces the RMS cycle when cell divisions associated with aleurone expansion and grain enlargement occur in the peripheral layers. © Springer-Verlag Berlin Heidelberg 2007.