Fern antheridiogen: Cancellation of a light-dependent block to antheridium formation

In the light (200 ft-c), prothalli of Onoclea sensibilis failed to form antheridia at any stage of development unless they were exposed to the antheridium-inducing hormone of Pteridium aquilinum (abbreviation: A_Pt). If prothalli pregrown for 7 days in the light were transferred to near-darkness (ca. 0.8 ft-c), plus sucrose, then antheridium formation set in spontaneously ca. 15–19 days after transfer.Prothalli exposed to near-darkness, plus sucrose, plus A_Pt, began to form antheridia within 4 days. This lag period was shortened to 3 and 2 days if, after transfer to near-darkness, the prothalli were exposed to A_Pt with a delay of 5 and 12 days, respectively. These, and other results, led to the conclusion that a block to antheridium formation gradually decayed upon exposure to near-darkness and was reestablished in the light within 24–36 hr. The sucrose requirement for antheridium formation in near-darkness became operative after the block to antheridium formation had decayed. Antheridiogen was not detected during spontaneous antheridium formation in near-darkness.The results suggest that A_Pt and near-darkness interchangeably cancel a light-dependent block to antheridium formation, A_Pt acting more promptly than near-darkness.The observations indicate that this block must remain canceled while initials emerge and undergo differentiation.