Investigation of Photosystem II functional size in higher plants under physiological and stress conditions using radiation target analysis and sucrose gradient ultracentrifugation

Authors: GIARDI, MARIA - National Research Council - Italy; ANTONACCI, AMINA - National Research Council - Italy; TOULOUPAKIS, ELEFTHERIOS - National Research Council - Italy; Mattoo, Autar

Submitted to: Molecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2022
Publication Date: 9/5/2022
Citation: Giardi, M.T., Antonacci, A., Touloupakis, E., Mattoo, A.K. 2022. Investigation of Photosystem II functional size in higher plants under physiological and stress conditions using radiation target analysis and sucrose gradient ultracentrifugation. Molecules. 27:5708. https://doi.org/10.3390/molecules27175708.
DOI: https://doi.org/10.3390/molecules27175708

Interpretive Summary: Plant life is dependent upon the rigor with which they can photosynthesize and produce food. One of the rate-limiting protein complexes which is critical for photosynthesis is made up of two proteins called D1 and D2. Both proteins have a short half-life, D1 having the shortest. Understanding how the D1/D2 proteins coordinate their function(s) within the chloroplast (plastids) is critical to developing strategies to increase food production. Toward that goal, this work studied the minimal functional size important for photosynthetic activity of D1/D2 proteins. In addition, the work focused on the effects of extreme abiotic stress on these proteins and the data suggest that the ‘dimeric’ D1/D2 complexes are advantageous in maintaining plant life under extreme abiotic stresses such as heat and drought. This work is important to plant biologists, photosynthesis researchers, students studying biology and food industry.

Technical Abstract: The Photosystem II (PSII) reaction centre is critical supramolecular pigment-protein complex in the chloroplast which catalyzes the light-induced transfer of electrons from water to plastoquinone. Structural studies have demonstrated the existence of an oligomeric Photosystem II. We carried out radiation inactivation target (RTA) analysis, which determines the minimum functional size of PSII, together with sucrose gradient ultracentrifugation (SGU) in vivo and in vitro on leaves from eight diverse plant species. Two PSII populations made of dimeric and monomeric core particles were revealed. However, this core distribution was not ubiquitous in the higher plants. Only one core population, a monomeric in case of Vicia faba and a dimeric core in Triticum durum mutant, respectively, were detected. Increasing the detergent concentration led to increased number of oligomeric core populations. The minimum PSII functional sizes measured in vivo as decay of the maximum quantum yield of PSII for primary photochemistry (Fv/Fm ratio) were in the range of 75-101±18 kDa, 2 to 3 times lower than that determined in vitro. Two abiotic stresses, heat or drought, individually imposed on the plants increased the content of the dimeric core in SGU and the minimum functional size determined by RTA in vivo. These data suggest that in vivo PSII functions as a monomer under normal conditions, however, under stress conditions it works as a dimer. The dimeric PSII structure in vivo may be advantageous in maintaining the activity under extreme abiotic stresses.