AP BIOLOGY

Detailed explanation-1: -These results indicate that phyA mediates the FR promotion of flowering. Phytochromes are photointerconvertible molecules that interconvert between the FR-absorbing Pfr and the R-absorbing phytochrome (Pr) form. The Pfr is usually considered the physiologically active form, whereas Pr is the inactive form.

Detailed explanation-2: -Phytochrome acts as a molecular switch in response to red and far-red light. It occurs in two reversible conformations (Pr and Pfr), which absorb red light (R) and far-red light (FR) respectively.

Detailed explanation-3: -The phytochrome photoreceptors are proteins that bind a tetrapyrrole chromophore, allowing them to absorb light. These phytochromes exist in two photo-interconvertible forms: an inactive, red-absorbing “Pr” form and an active, far-red–absorbing “Pfr” form.

Detailed explanation-4: -Phytochromes could affect flowering by altering the phase of entrainment of the circadian clock (Somers et al. 1998), thus changing the coincidence between light and a critical circadian phase. Therefore, we examined the behavior of the circadian clock in the se5 mutant.

Detailed explanation-5: -Phytochrome pigment in plants exists in two interconvertible forms-Pr and Pfr. Pfr absorbs far-red light of 730 nm wavelength. The Pfr form is the active form that initiates biological responses.