title: Acclimation to intense light implies changes at the level of trimeric subunits involved in the structural organization of the main light-harvesting complex of photosystem II (LHCII) and their isoforms.
abstract: When plants are grown under stable light conditions their photosynthetic apparatus undergoes a long-term acclimation process. Acclimation to different light intensities involves changes in the organization and/or abundance of protein complexes in the thylakoid membranes. In this study, spinach plants were exposed to differing light intensities, and the structural organization of the major light-harvesting chlorophyll a/b-protein complex of photosystem II (LHCII) was investigated by analysing their trimeric subunits. Plants were exposed to three different light intensities, 100 μmol quanta m⁻² s⁻¹, 200 μmol quanta m⁻² s⁻¹ and an elevated light intensity, 400 μmol quanta m⁻² s⁻¹, sufficient to provoke a moderate stress response in the form of down regulation of PSII. "MicroRotofor" analysis showed the presence of LHCII with different pIs and revealed a clear decline in their abundance as light intensity increased from 100 to 400 μmol quanta m⁻² s⁻¹. The three subunits (Lhcb1, Lhcb2, Lhcb3) behaved differently from each other as: Lhcb1 decreased more significantly than Lhcb2, whereas Lhcb3 was reduced only at a light window at which Lhcb1 and Lhcb2 abundance has already been depleted under intense irradiation. Interestingly, we also found that isoforms of Lhcb1 subunit (Lhcb1.1; 1.2; 1.3) behaved differently in response to elevated light intensity, suggesting an essential role of these isoforms to light adaption and consequently explaining the presence of this multigenic family, often identified among higher plants.
authors.affiliation: Department of Ecology and Biology, Tuscia University, Largo dell'Università Snc, 01100 Viterbo, Italy. timperio@unitus.it
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Timperio
authors.forename: Federica
authors.initials: F
authors.lastname: Gevi
authors.forename: Luigi R
authors.initials: LR
authors.lastname: Ceci
authors.forename: Lello
authors.initials: L
authors.lastname: Zolla
mesh_terms: D000064:Acclimatization; D061146:Chlorophyll Binding Proteins / Q000378:metabolism / Q000528:radiation effects*; D015536:Down-Regulation; D008027:Light; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000528:radiation effects*; D020033:Protein Isoforms; D021122:Protein Subunits; D018724:Spinacia oleracea / Q000378:metabolism / Q000528:radiation effects*; D013312:Stress, Physiological; D020524:Thylakoids / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D061146:Chlorophyll Binding Proteins; D045332:Photosystem II Protein Complex; D020033:Protein Isoforms; D021122:Protein Subunits