Figure 3

Characterization of the sco1-1 mutant. A-J are from 5-d-old light-grown seedlings, while K and L are from 4-d-old dark-grown seedlings. Upon seedling germination in white-light, the cotyledons of sco1-1 (B) appear colorless compared to wild type (A), but leaves that emerge from the apical meristem are green like wild-type leaves. Chlorophyll autofluorescence and cotyledon cross sections show that sco1-1 cotyledon cells (D and F) are almost completely devoid of chloroplasts except in cells associated with the vasculature, while wild-type (C and E) show a normal complement of chloroplasts in cotyledon cells. The albinism phenotype of sco1-1 is not always complete and green cells can be found in some sco1-1 cotyledons, where they are typically located along the margins of the tissue (G). A cross section of a cotyledon (H) from such a variegated mutant shows cells with a normal complement of chloroplasts adjacent to cells devoid of chloroplasts. Ultrastructural analysis of chloroplasts in these 'sectored' sco1-1 cotyledon mesophyll cells (J) showed that they are similar to chloroplasts in wild-type cotyledons (I). Starch deposition in 4 d-old dark-grown wild-type (K) and sco1-1 hypocotyls (L) appears similar, indicating that amyloplast development is not severely affected in the sco1-1 mutant. Scale bars in I and J are 1 μm.