Fluorescent indices of bean seedlings leaves during de-etiolation

Abstract

The study of the processes of etiolation and de-etiolation in plant tissues, as well as the mechanisms regulating these processes, is of scientific interest for biophysics and ecology. Etiolation of seedlings is an evolutionary adaptation that increases the chances of plant survival, while subsequent de-etiolation of leaves leads to chlorophyll synthesis and the formation of an efficiently functioning photosynthetic apparatus. The intensity and duration of illumination are determining factors in the regulation of the de-etiolation process. To study the changes occurring in the photosynthetic apparatus of plants during these processes, the PAM fluorometry method can be used, which allows for the registration of a range of fluorescent indices and their kinetics (maximum quantum yield Fv/Fm = (Fm – F0)/Fm, effective quantum yield of photosystem II ФPSII = (Fm′−F)/Fm′, and non-photochemical quenching NPQ = Fm/Fm′ − 1). These indices are closely related to the state and functional activity of the photosynthetic apparatus and characterize the efficiency of primary energy conversion as well as the development of photoinhibition protection mechanisms. The aim of this work is to study the changes in the fluorescent indices and pigment composition of etiolated leaves of Vicia faba L. (with plants grown under natural light conditions used as a control). After the appearance of the third leaf tier, the etiolated seedlings were placed together with the control ones, and fluorescent indices and chlorophyll content were recorded daily. During de-etiolation, plants grown under low light showed a rapid increase in initially low values of Fv/Fm, ФPSII, and NPQ. The equalization of these indices with those of control plants occurred within two days after placing the etiolated seedlings in natural light conditions. At the same time, the chlorophyll content in the leaves of etiolated seedlings reached control values significantly later. Additionally, etiolated samples exhibited non-monotonic kinetics of the NPQ coefficient, with a maximum recorded at 2-3 minutes after turning on actinic light. This peak disappeared by the 8th day of measurements, and the kinetics became indistinguishable from those of control samples. The data obtained on the dynamics of adaptation of etiolated plants to high light conditions may indicate different rates of development of complexes responsible for the light and dark stages of photosynthesis.

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Anna V. Mikhalkova
Faculty of Physics, Lomonosov Moscow State University
Russia

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