Photodormant

Photodormant describes seeds or other propagules whose germination is regulated by light. In photodormant species, the transition from dormancy to germination typically requires exposure to light, while darkness can keep seeds dormant or delay germination. The light requirement is called photodormancy and may be temporary or change with after-ripening.

Physiological basis: The primary photoreceptors are phytochromes, which switch between Pr (inactive) and Pfr (active) forms in response to red and far-red light. Red light promotes conversion to Pfr and often triggers germination, whereas far-red light shifts back to Pr and inhibits it. Blue light via cryptochromes and phototropins can modulate sensitivity and the timing of germination, depending on the species and seed state.

Ecology and examples: Photodormancy helps seeds time germination to favorable conditions at the soil surface. Lettuce seeds (Lactuca sativa) are a classic example of photodormant seeds. Other species in various plant families show light-dependent germination as an adaptive trait to prevent germination beneath litter or in overly deep soil.

Management implications: For crops and restoration, sowing depth, light exposure during germination tests, and light management in nurseries influence germination uniformity in photodormant species. In agricultural settings, adjusting light quality and duration near sowing depth can improve stand establishment.

See also: photomorphogenesis; phytochrome; skotodormancy; seed dormancy.