Final answer:
During the Seedbed Years in agriculture, PR (Phytochrome Red) was first used to determine if there was any light available for plants to grow. It played a crucial role in the germination of small seeds like lettuce, ensuring that seedlings reached the surface and received sufficient sunlight to grow.
Step-by-step explanation:
During the Seedbed Years, PR, or Phytochrome Red, was first used in agriculture to determine if there was any light for plants to grow.
In species with small seeds, like lettuce, it was important to ensure that the seedlings would reach the surface and receive sunlight in order to grow properly.
In the dark, phytochrome is in the Pr (inactive) form, causing the seeds to remain dormant.
However, upon exposure to light, Pr is converted to Pfr (active form) and germination proceeds.