Fig. 2. Genetic screen for ise mutants Mature Arabidopsis siliques contain about 60 seeds; roughly half are drawn for simplicity. Dark green seeds contain wild-type embryos, and light green seeds contain defective embryos. Embryos were released from their seed coats (sc) and viewed under bright-field illumination. In the example diagrammed here, wild-type is dark green and has reached the mid-torpedo stage, while the mutant is light green and retarded in morphological development (see Fig. 6B,C,D for in vivo results). Embryos were incubated with 10 kDa F-dextran for 5 minutes at room temperature, washed extensively, then viewed by fluorescence microscopy. Wild-type (wt) and most morphologically defective embryos emit red autoflorescence due to cholorophyll, and are unable to transport 10 kDa dextran (left bottom panel). A small fraction of embryo-defective lines (called increased size exclusion of plasmodesmata, ise) take up and allow movement of 10 kDa F-dextran, and thus exhibit green fluorescence (right bottom panel).