Fig. 5.

Nucellar cells proximal to the expanding endosperm exhibit features consistent with progression through PCD. (A) Early in the process of PCD, nucellar cells have a large single central vacuole, regular nuclei, and the typical complement of organelles. (B and C) With progression through PCD, the tonoplast becomes electron dense (B), and there is a marked vesiculation of the cells (indicated by asterisks). Nuclei become convoluted (C and Inset), the cytoplasm pulls away from the cell wall (arrowheads in C), and ER and organelles swell (lower and upper cell in C). cw, cell wall; m, mitochondrion; N, nucleus; nu, nucleolus; p, proplastid; r, ricinosome; t, tonoplast; v, vacuole; ^*, vesicles. (Bar in A,5 μm; bars in B and C,1 μm.)