Biosynthesis of non-fluorescent chlorophyll of Photosystem II core in greening plant leaves.: Effect of etiolated plants growing under heat shock conditions (38 °C)

Preliminary dark incubation of etiolated pea and maize plants at 38 degrees C allowed to observe a new dark reaction of Chl biosynthesis occuring after photoconversion of protochlorophyllide Pchld 655/650 into chlorophyllide Chld 684/676. This reaction was accompanied by chlorophyllide esterification and by the bathochromic shift of pigment spectra: Chld 684/676 --> Chl 688/680. After completion of the reaction, a rapid (20-30 s at 26 degrees C) quenching of Chl 688/680 low-temperature fluorescence was observed. The reaction Chld 684/676 --> Chl 688/680 was inhibited under anaerobic conditions as well as in the presence of KCN; the reaction accompanied by Chl fluorescence quenching was inhibited in the leaves of pea mutants with impaired function of Photosystem II reaction centers. The spectra position of newly formed Chl, effects of Chl fluorescence quenching allowed to assume that the new dark reaction is responsible for biosynthesis of P-680, the key pigment of Photosystem II reaction centres.