The light response in plants is a complex series of triggers and feedback loops using certain proteins in the cell to prepare and process light resulting in growth, flowering and straining toward light. The proteins responsible for light response are FHY3, FAR1, FHY1, FHL and phytochrome A.
Plants begin reacting to the absence of light by producing the pair of proteins known as FHY3 and FAR1. These two proteins increase the production of another pair of proteins known as FHY1 and FHL. The plant stockpiles these proteins so that it is able to respond to the light as soon as it is available. A protein known as phytochrome A detects light on the far-red end of the spectrum, beginning the plant’s light response before humans are able to see it.
When the phytochrome A is activated, it binds with FHY1 and FHL, which results in the accumulation of phytochrome A in the cell’s nucleus. Phytochrome A adjusts the activity of the genes in the cell nucleus that are responsible for the plant's development. When the gene activity changes, the plant responds with growth, flowering or straining toward the light. As more phytochrome A accumulates in the nucleus, less FHY3 and FAR1 are produced, creating a negative feedback loop that limits the plant’s light response.