Which of the following pigments is associated with the germination of seeds?

Concept: Phytochrome is a photoreceptor pigment found in plants that exists in two interconvertible forms: Pr (the biologically inactive form, which absorbs red light near 660 nm) and Pfr (the biologically active form, which absorbs far-red light near 730 nm). By switching between these two forms, phytochrome detects the presence, colour, and duration of light and controls light-dependent developmental processes such as seed germination, flowering time, and de-etiolation.

Application: In many light-sensitive (photoblastic) seeds, exposure to red light converts the inactive Pr form of phytochrome into the active Pfr form, which switches on the gene expression pathway needed for germination. Exposure to far-red light reverses this conversion, turning Pfr back into Pr and suppressing germination. This red/far-red reversible switch is the well-documented mechanism by which phytochrome regulates whether a seed germinates.

• Chlorophyll: the primary photosynthetic pigment that absorbs light energy and converts it into chemical energy during the light reactions of photosynthesis; it does not sense light quality or duration to trigger germination.

• Plastocyanin: a copper-containing electron-carrier protein that shuttles electrons between Cytochrome b6f and Photosystem I in the photosynthetic electron transport chain; it has no light-sensing or germination-triggering role.

• Xanthophyll: an accessory carotenoid pigment that broadens the range of light wavelengths captured for photosynthesis and provides photoprotection against excess light; it is not involved in triggering germination.

Result: So, among the pigments listed, phytochrome is the one whose red/far-red photoreversible switching is associated with the germination of seeds.