Ultrastructure of endosperm development in Arundo formosana Hack. (Poaceae) from differentiation to maturity

Abstract

Endosperm development of Arundo formosana Hack. is examined ultrastructurally and histochemically from differentiation to seed maturity. The differentiated endosperm contains four major cell types: the cells of the embryo surrounding region, transfer cells, aleurone layer, and starchy endosperm. After cellularization, cells of the embryo surrounding region and transfer cells contain dense cytoplasm and large quantities of rough endoplasmic reticulum (RER) and many dictyosomes. In the transfer cells, the wall ingrowths are present on the walls adjacent to the nucellus. The embryo surrounding region is distributed on the ventral side and surrounds the suspensor. After leaf primordium initiation, most cells of the embryo surrounding region have degenerated, but the outermost layer of the ventral side becomes part of the aleurone layer. The transfer cells differentiate into outer and inner cells. The outer transfer cells contain electron-dense cytoplasm, many oil bodies, large quantities of RER, and dictyosomes. These cells appear PAS-positive, especially in the thickening walls. The inner transfer cells have electron-transparent cytoplasm, some small vacuoles, organelles, and oil bodies. The outer transfer cells are finally compressed and degenerated. The inner cells contain PAS-positive thickening walls, many oil bodies, protein bodies, and RER at maturity. The starchy endosperm cells gradually accumulate reserves (mainly proteins and starch) during development, and are filled with amyloplasts and protein bodies at maturity. The protein bodies are of two types that originate in the RER and are then stored in the cisternal lumen of RER, and vacuoles, respectively. The outermost layer of the endosperm becomes the aleurone layer, except for the transfer cell region. The contents of the aleurone cells are initially similar to other starchy endosperm cells, and are finally filled with aleurone grains surrounded by many small lipid bodies. The aleurone grains are initiated from ER and accumulate in vacuoles.