The protochlorophyllide-chlorophyllide cycle.

The protochlorophyllide-chlorophyllide cycle was introduced by Sironval [1981, In: Akoyunoglou G (ed) Photosynthesis, Vol 5: Chloroplast Development, pp 3-14] to describe the interconvertion of the Pchlide and Chlide spectral forms occurring when nonilluminated leaves are irradiated for the first time. Since this original publication important progresses have been made at the physiological, biochemical and molecular levels. The understanding of the cycle and of its regulation are critical for the understanding of chlorophyll synthesis in photosynthetic organisms. In this contribution, I present an update version of the cycle in tissues illuminated for the first time, in greening and in green leaves, and in photosynthetic organisms, which are able to synthesize chlorophyll in the dark as well. To the descriptive part, an assay on the regulation of the cycle is added.