Chlorophyll fluorescence; Action spectra; Chloroplast avoidance reaction; Chloroplast accumulation reaction; Leaf absorption cross-section; Hordeum vulgare

Plants have developed many ways to protect reaction centres of photosystems against overexcitation. One of the mechanisms involves reduction of the leaf absorption cross-section by light-induced chloroplast avoidance reaction. Decrease in the probability of photon absorption by the pigments bound within photosystem II (PSII) complexes leads to the increase in quantum yield of PSII photochemistry (?PSII). On the other hand, the decrease of PSII excitation probability causes reduction of chlorophyll a fluorescence intensity which is manifested as the apparent increase of determined quantum yield of regulated light-induced non-photochemical quenching (?NPQ). Absorption of different light intensity by phototropins led to the different chloroplast distribution within barley leaves, estimated by measurement of the leaf transmittance. Due to a weak blue light used for transmittance measurements, leaves exposed to actinic light with wavelengths longer than 520 nm undergo chloroplast accumulation reaction, in contrast with leaves exposed to light with shorter wavelengths, that showed a different extent of chloroplast avoidance reaction. Based on the ?NPQ action spectra measured simultaneously with the transmittance, the influence of different chloroplast distribution on ?NPQ was assessed. The analysis of results showed that decrease in the leaf absorption cross-section due to increasing part of chloroplasts reaching profile position significantly affected the partitioning of excitation energy within PSII and such rearrangement also distorted measured ?NPQ and cannot be neglected in its interpretation. When the majority of chloroplastsreached profile position, the photoprotective effect appeared to be the most prominent for strong blue light that has the highest absorption in the upper leaf layers in comparison with green or red ones.