Photosystem II organisation in chloroplasts of Arum italicum leaf depends on tissue location
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The growth of plants under stable light quality induces long-term acclimation responses of the photosynthetic apparatus. Light can even cause variations depending on the tissue location, as in Arum italicum leaf, where chloroplasts are developed in the lamina and in the entire thickness of the petiole. We addressed the question whether differences in plastids can be characterised in terms of protein–protein interactions in the thylakoid membranes. Thylakoid assembly was studied in the palisade and spongy tissue of the lamina and in the outer parenchyma and inner aerenchyma of the petiole of the mature winter leaf of Arum italicum. The chlorophyll–protein complexes were analysed by means of blue-native-PAGE and fluorescence emission spectra. The petiole chloroplasts differ from those in the lamina in thylakoid composition: (1) reaction centres are scarce, especially photosystem (PS) I in the inner aerenchyma; (2) light-harvesting complex (LHC) II is abundant, (3) the relative amount of LHCII trimers increases, but this is not accompanied by increased levels of PSII–LHCII supercomplexes. Nevertheless, the intrinsic PSII functionality is comparable in all tissues. In Arum italicum leaf, the gradient in thylakoid organisation, which occurs from the palisade tissue to the inner aerenchyma of the petiole, is typical for photosynthetic acclimation to low-light intensity with a high enrichment of far-red light. The results obtained demonstrate a high plasticity of chloroplasts even in an individual plant. The mutual interaction of thylakoid protein complexes is discussed in relation to the photosynthetic efficiency of the leaf parts and to the ecodevelopmental role of light.
KeywordsArum Blue-native-PAGE Chlorophyll fluorescence Photosystem II Sun–shade acclimation Thylakoid
We are grateful to Sari Sirpiö and Eveliina Aro (University of Turku, Finland) for help in the BN technique and Yagut Allahverdiyeva-Rinne (University of Turku, Finland) for assistance in the 77 K analyses. The PSI A/B, the LHCII and Cyt f antibodies were kindly provided by Torill Hundal (Linköping University, Sweden), Roberto Barbato (University of Piemonte Orientale, Italy) and Lixin Zhang (Chinese Academy of Science, Peoples Republic of China), respectively. Elena Ferroni is thanked for the help in language editing. We are also grateful to the two anonymous referees for their highly appreciated suggestions. This research was supported by the University of Ferrara (Italy), with a fellowship to Laura Pantaleoni provided by the University Institute for Higher Studies (IUSS, Ferrara) 1391, and by the Academy of Finland.
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