photodormancy

Photodormancy is a type of seed dormancy that is broken by exposure to light. Seeds in photodormant states will not germinate when planted in darkness, even if other environmental conditions such as temperature and moisture are favorable. Upon exposure to light, the seeds become responsive to these favorable conditions and can then germinate. This phenomenon is common in many plant species, particularly those that grow in environments where light penetration to the soil surface is variable, such as in open fields or on forest floors.

The mechanism behind photodormancy often involves the photoreceptor phytochrome. Phytochrome exists in two interconvertible forms, Pr and Pfr. Light, particularly red light, converts Pr to Pfr. Far-red light converts Pfr back to Pr. The accumulation of Pfr in seeds is often the signal that breaks photodormancy. When seeds are buried or covered by soil, they are deprived of light, and the Pfr form may decrease, maintaining dormancy. When the soil is disturbed or the seed is brought closer to the surface, light exposure converts the remaining Pr to Pfr, allowing germination to proceed.

This light requirement ensures that seeds germinate only when they are likely to emerge from the soil and receive sufficient sunlight for photosynthesis. It acts as a protective mechanism against premature germination in unfavorable conditions. Understanding photodormancy is crucial in agriculture and ecological studies, aiding in seed germination protocols and predicting plant community dynamics.