A novel role for PsbO1 in photosynthetic electron transport as suggested by its light-triggered selective nitration inArabidopsis thaliana

Abstract

Exposure of Arabidopsis leaves to nitrogen dioxide (NO) results in the selective nitration of specific proteins, such as PsbO1. The 9th tyrosine residue (Tyr) of PsbO1 has been identified as the nitration site. This nitration is triggered by light and inhibited by photosynthetic electron transport inhibitors. During protein nitration, tyrosyl and NO radicals are formed concurrently and combine rapidly to form 3-nitrotyrosine. A selective oxidation mechanism for Tyr of PsbO1 is required. We postulated that, similar toTyr of D1, Tyr of PsbO1 is selectively photo-oxidized by photosynthetic electron transport in response to illumination to a tyrosyl radical. In corroboration, after reappraising our oxygen evolution analysis, the nitration of PsbO1 proved responsible for decreased oxygen evolution from the thylakoid membranes. NO is reportedly taken into cells as nitrous acid, which dissociates to form NO. NO may be oxidized into NO by the oxygen-evolving complex. Light may synchronize this reaction with tyrosyl radical formation. These findings suggest a novel role for PsbO1 in photosynthetic electron transport.

Nitrogen Dioxide at Ambient Concentrations Induces Nitration and Degradation of PYR/PYL/RCAR Receptors to Stimulate Plant Growth: A Hypothetical Model

“…This buffer contained NO 2 and NO 2 − as nitrating agent [61]. As it is reported that nitrite anion inhibits PSII to decrease oxygen evolution [72,73,74], it is necessary to separately evaluate these two effects of nitrite on the oxygen evolution. Thylakoid membranes isolated from Arabidopsis leaves were incubated in a buffer containing NO 2 and NO 2 − or a buffer containing NO 2 − alone in the light or in the dark [71].…”