[Investigation of the initial steps of protochlorophyllide photoreduction in etiolated plants].

The irreversible nonfluorescent product of the protochlorophyllide photoreduction with the wide electronic band at 705 nm was discovered. The P705 product through the intermediate products with the fluorescence max at 695 nm and 687 nm turns into Chl684 678, as the result of heating in darkness. The P705, P695, P687 products quench protochlorophyllide fluorescence with great efficiency. Analysis of the intermediate product properties allow to propose a new photoreduction mechanism that includes energy transfer to the trapping center where the charge transfer is performed, nonradiative energy dissipation in the charge-transfer complex, and protonation and disproportionation of the pigment anion-radicals.