Protochlorophyllide,[1] or monovinyl protochlorophyllide, is an intermediate in the biosynthesis of chlorophyll a. It lacks the phytol side-chain of chlorophyll and the reduced pyrrole in ring D.[2] Protochlorophyllide is highly fluorescent; mutants that accumulate it glow red if irradiated with blue light.[3] In angiosperms, the later steps which convert protochlorophyllide to chlorophyll are light-dependent, and such plants are pale (chlorotic) if grown in the darkness.