Active Oxygen Produced during Selective Excitation of Photosystem I Is Damaging Not Only to Photosystem I, but Also to Photosystem II

• Published in: Plant physiology (Bethesda) 2001-04, Vol.125 (4), p.2007-2015
• Main Authors: Staffan Erling Tjus, Henrik Vibe Scheller, Andersson, Bertil, Møller, Birger Lindberg
• Format: Article
• Language: English
• Subjects: Bioenergetics and Photosynthesis; Biological and medical sciences; Cell Fractionation; Chlorophyll - metabolism; Chlorophylls; Chloroplasts - metabolism; Darkness; Electron Transport; Fundamental and applied biological sciences. Psychology; Guanosine Triphosphate - metabolism; Hydrogen; Light; Light-Harvesting Protein Complexes; MEDICIN; MEDICINE; Metabolism; Oxidation-Reduction; Oxygen - metabolism; Peroxides; Photoinhibition; Photosynthesis, respiration. Anabolism, catabolism; Photosynthetic Reaction Center Complex Proteins - metabolism; Photosynthetic Reaction Center Complex Proteins - radiation effects; Photosystem I; Photosystem I Protein Complex; Photosystem II; Photosystem II Protein Complex; Plant physiology and development; Plants; Reactive oxygen species; Spinacia oleracea - metabolism; Superoxides; Thylakoids; Thylakoids - metabolism; Thylakoids - radiation effects; Thylakoids - ultrastructure
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.125.4.2007

With the aim to specifically study the molecular mechanisms behind photoinhibition of photosystem I, stacked spinach (Spinacia oleracea) thylakoids were irradiated at 4°C with far-red light (>715 nm) exciting photosystem I, but not photosystem II. Selective excitation of photosystem I by far-red light for 130 min resulted in a 40% inactivation of photosystem I. It is surprising that this treatment also caused up to 90% damage to photosystem II. This suggests that active oxygen produced at the reducing side of photosystem I is highly damaging to photosystem II. Only a small pool of the D1-protein was degraded. However, most of the D1-protein was modified to a slightly higher molecular mass, indicative of a damage-induced conformational change. The far-red illumination was also performed using destacked and randomized thylakoids in which the distance between the photosystems is shorter. Upon 130 min of illumination, photosystem I showed an approximate 40% inactivation as in stacked thylakoids. In contrast, photosystem II only showed 40% inactivation in destacked and randomized thylakoids, less than one-half of the inactivation observed using stacked thylakoids. In accordance with this, photosystem II, but not photosystem I is more protected from photoinhibition in destacked thylakoids. Addition of active oxygen scavengers during the far-red photosystem I illumination demonstrated superoxide to be a major cause of damage to photosystem I, whereas photosystem II was damaged mainly by superoxide and hydrogen peroxide.