Effects of Nuclear y Mutations on Expression of Plastid Genes Required for Light-Independent Chlorophyll Formation in Chlamydomonas

Abstract

During evolution two distinct mechanisms were established for the reduction of protochlorophyllide (pchlide) to chlorophyllide (chlide), a key step in the chlorophyll biosynthesis pathway. One mechanism, catalyzed by the enzyme NADPH: protochlorophyllide oxidoreductase (POR), is completely dependent upon light for its activity [1–2]. Light-dependent POR is present in cyanobacteria, green algae, most non-vascular and vascular plants, and is the only mechanism used for chlorophyll formation in angiosperms. The second mechanism, present in anoxygenic photosynthetic bacteria as well as cyanobacteria, non-vascular plants, ferns and gymnosperms, is capable of reducing pchlide to chlide in a light-independent manner [3]. All organisms containing this mechanism for pchlide reduction are capable of chlorophyll formation in the dark. While a significant amount of information is now available on the regulation of POR biosynthesis and activity [1], little is known about the enzyme mediating light-independent pchlide reduction (designated LIPOR), the factors that regulate its formation, and its requirements for catalytic function [3].