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.