High-energy state of chloroplasts measured as function of light induced changes of delayed fluorescence and energetic effectivity of photosynthesis of pea leaves
1990
Morgun, V.N. | Doldzhikov, S.V. (Agricultural Inst., Krasnoyarsk (USSR))
The chlorophyll delayed fluorescence (DF) is a useful tool to characterize the functional state of plants. Quantum yield and decay kinetics of DF depend on the rate of photosynthetic electron transport and membrane potential of thylakoids. After an irradiation of dark-adapted plants, DF displays light-induced transients simultaneously with a photosynthesis induction. During the DF induction the emission shows fast and irregular rise to maximum P which is followed by a slow decline to a steady-state level S. Parameters of DF induction correlate with the rate of CO2 fixation, and may be used for estimation of photosynthetic activity under normal and stress conditions. Nevertheless, the DF implications are limited for absence of a distinct concept of DF light dependence. In the early works the discrepancy between the "light curves" of DF and of photosynthesis was stressed, as DF showed no saturation with radiant energy, probably due to recording emission in transmitted radiation. Slight saturation was observed on both the P- and S-levels of DF induction in reflected radiation by Grigor'ev et al. (1983). The DF yield increases exponentially with a rise of the electrochemical potential difference in the thylakoid membrane. Therefore, the DF intensity may be a power function of irradiance (I) and the shape of the "light curves" is determined by this fact. The analysis of interrelation of electron transport rate and chloroplast DF confirms such a supposition. We tested the exponential nature of the DF response curves to I in native leaves and their relation to thylakoid energization.
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