Studies of the early photoactive forms of the chlorophyll precursor in the plant leaves using fluorescence spectroscopy at 20°C

Abstract

Using fluorescence spectroscopic method, accumulation of several forms of the chlorophyll precursor at the early stages of their formation at 20°C has been observed, due to the lowered intensity of the excitation light applied for inhibition of the photoreaction. A high quantum yield of the initial fluorescence of the short-wavelength (638 nm) form of the embryonic leaves sharply falls down with the accumulation of the pigment precursor. The fluorescence yield of its main form with a maximum at 653 nm is decreased less drastically. At the temperature of −196°C, an intensive increase in fluorescence yield is observed, particularly pronounced (10-fold) for the main 655 nm form of the precursor. Changes in the fluorescence spectra observed in the course of the photoconversion testify to the fact that at the early stages of the chlorophyll biosynthesis only the first of two sequential reactions of photoreduction proceeds in vivo. A complicated character of the kinetic curves of fluorescence in the course of the photoreaction is attributable to the effects of the concentration change and changes in the quantum yields of the converting forms.