Illumination of etiolated maize leaves with low-intensity light produces a chlorophyll/pheophytin-containing complex. The complex contains two native chlorophyll forms Ch1671/668 and Ch1675/668 as well as pheophytin Pheo 679/675 (with chlorophyll/pheophytin ratio of 2/1). The complex is formed in the course of two successive reactions: reaction of protochlorophyllide Pchlde 655/650 photoreduction resulted in chlorophyllide Chide 684/676 formation, and the subsequent dark reaction of Chide 684β’676 involving Mg substitution by H2 in pigment chromophore and pigment esterification by phytol. Out data show that the reaction leading to chlorophyll/pheophytin-containing complex formation is not destructive. The reaction is in fact biosynthetic, and is competitive with the known reactions of biosynthesis of the bulk of chlorophyll molecules. The relationship between chlorophyll and pheophytin biosynthesis reactions is controlled by temperature, light intensity and exposure duration.
The native complex containing pheophytin a and chlorophyll a is supposed to be a direct precursor of the PS II reaction centre in plant leaves.
Abbreviations: Chl -chlorophyll; Chide-chlorophyllide; Pchl-protochlorophyll; Pchlde-protochloropyllide; Pheo -pheophytin; PS II RC -Photosystem II reaction centres. Abbreviations for native pigment forms: the first number after pigment symbol corresponds to the maximum position of low-temperature fluorescence band (nm); the second number corresponds to the maximum position of long wave absorption band