The induced sector Arabidopsis apical embryonic fate map
Alexandria Saulsberry1,*,
Paula R. Martin1,
Tim O’Brien2,
Leslie E. Sieburth3 and
F. Bryan Pickett1,
1 Department of Biology, Loyola University of Chicago, 6525 N. Sheridan Road, Chicago, IL 60626, USA
2 Department of Mathematics and Statistics, Loyola University of Chicago, 6525 N. Sheridan Road, Chicago, IL 60626, USA
3 Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA
* Present address: Pritzker School of Medicine, University of Chicago, 5841 S. Maryland Avenue, Chicago, IL, 60637, USA
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Fig. 1. Embryonic stage of induction of GUS–|GUS+ genetic chimeras. Whole ovules within gynoecia were sectioned and stained 2 days after fertilization (A,B) or 8 days after fertilization following no heat shock on day 2 (C) or a heat shock on day 2 (D). All embryos sectioned 2 days after fertilization had either a single apical and basal cell (A) or two apical cells separated by an anticlinal cell wall and two basal cells separated by a periclinal cell wall (B). Thus at the time of GUS– sector induction one or two apical cells were present in embryos. Eight days after fertilization both heat-shocked (D) and control (C) embryos were in the late heart to early torpedo stage of development, showing well developed cotyledon primordia and a root apex, suggesting that transient heat shock at the two-cell stage does not seriously disrupt later embryogenesis. ac, apical cell; bc, basal cell; cot, cotyledon primordia. Size bar: 10 µm.
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Fig. 2. Patterns of GUS– sector sharing seen in mature chimeric plants after sector induction at the two-apical-cell stage of embryogenesis. All plants are shown with clockwise phyllotaxy to permit easy visual comparison of sector sharing patterns. GUS– cell sectors are visualized as white tissue after clearing plants with ethanol while GUS+ cells retain blue coloration (A-H). Most GUS– sectors included all cells in one cotyledon and extended into physically adjacent organs (A,B) but many sectors also included one whole cotyledon and either the left or right margin of the other cotyledon (C). Rarer sectors extended either between cotyledons on the same side of the frontal longitudinal plane (D) or extended between the cotyledons but crossed the frontal plane (E). Most chimeras had sector boundaries that either separated the left and right margins of leaf 1 or leaf 2 (A,E,G-H) or separated the left and right margins of both leaf 1 and leaf 2 (B,F) which is reflected in the map as a tendency for GUS– sectors not to be shared between organs that lie across the sagittal longitudinal plane of the embryo. C1 and C2, cotyledon 1 and 2; 1-4, true leaves 1-4.
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Fig. 3. Distribution of GUS– sector sizes among the population of 319 GUS–|GUS+ chimeras generated in this experiment. Chimeras were classified as having between 1 and 11 GUS– organ marginal regions on the basis of visual scoring. Local maxima in numbers of plants were seen at 3, 6 and 9 GUS– regions, roughly corresponding to plants that were 1/4, 1/2 or 3/4 GUS– in total organ area. Plants that are wholly GUS– (12 marginal regions GUS–) are not included because they are not apical chimeras and were not used for fate mapping.
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Fig. 4. Patterns of sector adjacency were scored for all chimeras used in this study. For this graph, only GUS– sectors in cotyledons and leaf 1 and 2 were scored for adjacency; these organs were selected because they are the oldest organs, with cotyledons being specified during embryonic development and leaf specification occurring soon after germination. The eight margins of these four organs were scored, however plants with only one, or those with seven or more, GUS– margins were omitted as their GUS– regions were wholly entire by default. The numbers of chimeric plants of a given sector size (two to six margins) are separated into chimeras with contiguous sectors and chimeras with non-contiguous sectors. Black bars show numbers of plants with the indicated number of GUS– margins whose sectors are wholly adjacent and white bars show the numbers of plants whose GUS– sectors show non-adjacency.
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Fig. 5. Results of multidimensional scaling analysis. This plot was prepared by clustering marginal regions based on the first two primary dimensions identified in the pairwise distance matrix. The first dimension accounts for the greatest axis of dissimilarity in the data, and clusters margins from the two cotyledons and their close-mapping partners away from each other across the sagittal longitudinal plane. The second dimension accounts for the next largest degree of dissimilarity in the data, and clusters the left and right margins of the cotyledons and leaf 4 away from each other across the frontal longitudinal plane. Both dimensions account for 93.7% of the variation in the original data matrix. Taken together these data highlight the fact that the daughters of the first apical cell division are not randomly apportioned to all organ margins with uniform frequency. C1L, C1R, C2L and C2R indicate the left and right margin, respectively, of cotyledon 1 and 2. Other labels similarly indicate the left and right marginal regions of true leaves 1-4.
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© The Company of Biologists Ltd 2002
