Action of light and gibberellic acid on the growth of excised embryos from Phacelia tanacetifolia seeds.

Germination of Phacelia tanacetifolia seeds is inhibited by light. Embryos freed of endosperm grow irrespective of light. However, if they are held in 0.3 M mannitol plus 2% sucrose, light sensitivity is reinstated: growth (i. e., germination) occurs in darkness but not in light. Gibberellic acid (GA3) releases the inhibition due to light. These results suggest that (a) the photoreceptor site of the seed is in the embryo; (b) GA3 acts directly on the embryo; and (c) darkimbibed embryos appear to have a higher water-uptake potential.